There are concerns about memory leaks from extensive use of memory cgroups
as each memory cgroup creates its own set of kmem caches.  There is a
possiblity that the memcg kmem caches may remain even after the memory
cgroups have been offlined.  Therefore, it will be useful to show the
status of each of memcg kmem caches.

This patch introduces a new <debugfs>/memcg_slabinfo file which is
somewhat similar to /proc/slabinfo in format, but lists only information
about kmem caches that have child memcg kmem caches.  Information
available in /proc/slabinfo are not repeated in memcg_slabinfo.

A portion of a sample output of the file was:

  # <name> <css_id[:dead]> <active_objs> <num_objs> <active_slabs> <num_slabs>
  rpc_inode_cache   root          13     51      1      1
  rpc_inode_cache     48           0      0      0      0
  fat_inode_cache   root           1     45      1      1
  fat_inode_cache     41           2     45      1      1
  xfs_inode         root         770    816     24     24
  xfs_inode           92          22     34      1      1
  xfs_inode           88:dead      1     34      1      1
  xfs_inode           89:dead     23     34      1      1
  xfs_inode           85           4     34      1      1
  xfs_inode           84           9     34      1      1

The css id of the memcg is also listed. If a memcg is not online,
the tag ":dead" will be attached as shown above.

[longman@redhat.com: memcg: add ":deact" tag for reparented kmem caches in memcg_slabinfo]
  Link: http://lkml.kernel.org/r/20190621173005.31514-1-longman@redhat.com
[longman@redhat.com: set the flag in the common code as suggested by Roman]
  Link: http://lkml.kernel.org/r/20190627184324.5875-1-longman@redhat.com
Link: http://lkml.kernel.org/r/20190619171621.26209-1-longman@redhat.comSigned-off-by: NWaiman Long <longman@redhat.com>
Suggested-by: NShakeel Butt <shakeelb@google.com>
Reviewed-by: NShakeel Butt <shakeelb@google.com>
Acked-by: NRoman Gushchin <guro@fb.com>
Acked-by: NDavid Rientjes <rientjes@google.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Let's reparent non-root kmem_caches on memcg offlining.  This allows us to
release the memory cgroup without waiting for the last outstanding kernel
object (e.g.  dentry used by another application).

Since the parent cgroup is already charged, everything we need to do is to
splice the list of kmem_caches to the parent's kmem_caches list, swap the
memcg pointer, drop the css refcounter for each kmem_cache and adjust the
parent's css refcounter.

Please, note that kmem_cache->memcg_params.memcg isn't a stable pointer
anymore.  It's safe to read it under rcu_read_lock(), cgroup_mutex held,
or any other way that protects the memory cgroup from being released.

We can race with the slab allocation and deallocation paths.  It's not a
big problem: parent's charge and slab global stats are always correct, and
we don't care anymore about the child usage and global stats.  The child
cgroup is already offline, so we don't use or show it anywhere.

Local slab stats (NR_SLAB_RECLAIMABLE and NR_SLAB_UNRECLAIMABLE) aren't
used anywhere except count_shadow_nodes().  But even there it won't break
anything: after reparenting "nodes" will be 0 on child level (because
we're already reparenting shrinker lists), and on parent level page stats
always were 0, and this patch won't change anything.

[guro@fb.com: properly handle kmem_caches reparented to root_mem_cgroup]
  Link: http://lkml.kernel.org/r/20190620213427.1691847-1-guro@fb.com
Link: http://lkml.kernel.org/r/20190611231813.3148843-11-guro@fb.comSigned-off-by: NRoman Gushchin <guro@fb.com>
Acked-by: NVladimir Davydov <vdavydov.dev@gmail.com>
Reviewed-by: NShakeel Butt <shakeelb@google.com>
Acked-by: NDavid Rientjes <rientjes@google.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Waiman Long <longman@redhat.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Andrei Vagin <avagin@gmail.com>
Cc: Qian Cai <cai@lca.pw>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Currently each charged slab page holds a reference to the cgroup to which
it's charged.  Kmem_caches are held by the memcg and are released all
together with the memory cgroup.  It means that none of kmem_caches are
released unless at least one reference to the memcg exists, which is very
far from optimal.

Let's rework it in a way that allows releasing individual kmem_caches as
soon as the cgroup is offline, the kmem_cache is empty and there are no
pending allocations.

To make it possible, let's introduce a new percpu refcounter for non-root
kmem caches.  The counter is initialized to the percpu mode, and is
switched to the atomic mode during kmem_cache deactivation.  The counter
is bumped for every charged page and also for every running allocation.
So the kmem_cache can't be released unless all allocations complete.

To shutdown non-active empty kmem_caches, let's reuse the work queue,
previously used for the kmem_cache deactivation.  Once the reference
counter reaches 0, let's schedule an asynchronous kmem_cache release.

* I used the following simple approach to test the performance
(stolen from another patchset by T. Harding):

    time find / -name fname-no-exist
    echo 2 > /proc/sys/vm/drop_caches
    repeat 10 times

Results:

        orig		patched

real	0m1.455s	real	0m1.355s
user	0m0.206s	user	0m0.219s
sys	0m0.855s	sys	0m0.807s

real	0m1.487s	real	0m1.699s
user	0m0.221s	user	0m0.256s
sys	0m0.806s	sys	0m0.948s

real	0m1.515s	real	0m1.505s
user	0m0.183s	user	0m0.215s
sys	0m0.876s	sys	0m0.858s

real	0m1.291s	real	0m1.380s
user	0m0.193s	user	0m0.198s
sys	0m0.843s	sys	0m0.786s

real	0m1.364s	real	0m1.374s
user	0m0.180s	user	0m0.182s
sys	0m0.868s	sys	0m0.806s

real	0m1.352s	real	0m1.312s
user	0m0.201s	user	0m0.212s
sys	0m0.820s	sys	0m0.761s

real	0m1.302s	real	0m1.349s
user	0m0.205s	user	0m0.203s
sys	0m0.803s	sys	0m0.792s

real	0m1.334s	real	0m1.301s
user	0m0.194s	user	0m0.201s
sys	0m0.806s	sys	0m0.779s

real	0m1.426s	real	0m1.434s
user	0m0.216s	user	0m0.181s
sys	0m0.824s	sys	0m0.864s

real	0m1.350s	real	0m1.295s
user	0m0.200s	user	0m0.190s
sys	0m0.842s	sys	0m0.811s

So it looks like the difference is not noticeable in this test.

[cai@lca.pw: fix an use-after-free in kmemcg_workfn()]
  Link: http://lkml.kernel.org/r/1560977573-10715-1-git-send-email-cai@lca.pw
Link: http://lkml.kernel.org/r/20190611231813.3148843-9-guro@fb.comSigned-off-by: NRoman Gushchin <guro@fb.com>
Signed-off-by: NQian Cai <cai@lca.pw>
Acked-by: NVladimir Davydov <vdavydov.dev@gmail.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Waiman Long <longman@redhat.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Andrei Vagin <avagin@gmail.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Currently the memcg_params.dying flag and the corresponding workqueue used
for the asynchronous deactivation of kmem_caches is synchronized using the
slab_mutex.

It makes impossible to check this flag from the irq context, which will be
required in order to implement asynchronous release of kmem_caches.

So let's switch over to the irq-save flavor of the spinlock-based
synchronization.

Link: http://lkml.kernel.org/r/20190611231813.3148843-8-guro@fb.comSigned-off-by: NRoman Gushchin <guro@fb.com>
Acked-by: NVladimir Davydov <vdavydov.dev@gmail.com>
Reviewed-by: NShakeel Butt <shakeelb@google.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Waiman Long <longman@redhat.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Andrei Vagin <avagin@gmail.com>
Cc: Qian Cai <cai@lca.pw>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

There is no point in checking the root_cache->memcg_params.dying flag on
kmem_cache creation path.  New allocations shouldn't be performed using a
dead root kmem_cache, so no new memcg kmem_cache creation can be scheduled
after the flag is set.  And if it was scheduled before,
flush_memcg_workqueue() will wait for it anyway.

So let's drop this check to simplify the code.

Link: http://lkml.kernel.org/r/20190611231813.3148843-7-guro@fb.comSigned-off-by: NRoman Gushchin <guro@fb.com>
Acked-by: NVladimir Davydov <vdavydov.dev@gmail.com>
Reviewed-by: NShakeel Butt <shakeelb@google.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Waiman Long <longman@redhat.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Andrei Vagin <avagin@gmail.com>
Cc: Qian Cai <cai@lca.pw>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Currently SLUB uses a work scheduled after an RCU grace period to
deactivate a non-root kmem_cache.  This mechanism can be reused for
kmem_caches release, but requires generalization for SLAB case.

Introduce kmemcg_cache_deactivate() function, which calls
allocator-specific __kmem_cache_deactivate() and schedules execution of
__kmem_cache_deactivate_after_rcu() with all necessary locks in a worker
context after an rcu grace period.

Here is the new calling scheme:
  kmemcg_cache_deactivate()
    __kmemcg_cache_deactivate()                  SLAB/SLUB-specific
    kmemcg_rcufn()                               rcu
      kmemcg_workfn()                            work
        __kmemcg_cache_deactivate_after_rcu()    SLAB/SLUB-specific

instead of:
  __kmemcg_cache_deactivate()                    SLAB/SLUB-specific
    slab_deactivate_memcg_cache_rcu_sched()      SLUB-only
      kmemcg_rcufn()                             rcu
        kmemcg_workfn()                          work
          kmemcg_cache_deact_after_rcu()         SLUB-only

For consistency, all allocator-specific functions start with "__".

Link: http://lkml.kernel.org/r/20190611231813.3148843-4-guro@fb.comSigned-off-by: NRoman Gushchin <guro@fb.com>
Acked-by: NVladimir Davydov <vdavydov.dev@gmail.com>
Reviewed-by: NShakeel Butt <shakeelb@google.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Waiman Long <longman@redhat.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Andrei Vagin <avagin@gmail.com>
Cc: Qian Cai <cai@lca.pw>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

The delayed work/rcu deactivation infrastructure of non-root kmem_caches
can be also used for asynchronous release of these objects.  Let's get rid
of the word "deactivation" in corresponding names to make the code look
better after generalization.

It's easier to make the renaming first, so that the generalized code will
look consistent from scratch.

Let's rename struct memcg_cache_params fields:
  deact_fn -> work_fn
  deact_rcu_head -> rcu_head
  deact_work -> work

And RCU/delayed work callbacks in slab common code:
  kmemcg_deactivate_rcufn -> kmemcg_rcufn
  kmemcg_deactivate_workfn -> kmemcg_workfn

This patch contains no functional changes, only renamings.

Link: http://lkml.kernel.org/r/20190611231813.3148843-3-guro@fb.comSigned-off-by: NRoman Gushchin <guro@fb.com>
Acked-by: NVladimir Davydov <vdavydov.dev@gmail.com>
Reviewed-by: NShakeel Butt <shakeelb@google.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Waiman Long <longman@redhat.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Andrei Vagin <avagin@gmail.com>
Cc: Qian Cai <cai@lca.pw>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Patch series "mm: reparent slab memory on cgroup removal", v7.

# Why do we need this?

We've noticed that the number of dying cgroups is steadily growing on most
of our hosts in production.  The following investigation revealed an issue
in the userspace memory reclaim code [1], accounting of kernel stacks [2],
and also the main reason: slab objects.

The underlying problem is quite simple: any page charged to a cgroup holds
a reference to it, so the cgroup can't be reclaimed unless all charged
pages are gone.  If a slab object is actively used by other cgroups, it
won't be reclaimed, and will prevent the origin cgroup from being
reclaimed.

Slab objects, and first of all vfs cache, is shared between cgroups, which
are using the same underlying fs, and what's even more important, it's
shared between multiple generations of the same workload.  So if something
is running periodically every time in a new cgroup (like how systemd
works), we do accumulate multiple dying cgroups.

Strictly speaking pagecache isn't different here, but there is a key
difference: we disable protection and apply some extra pressure on LRUs of
dying cgroups, and these LRUs contain all charged pages.  My experiments
show that with the disabled kernel memory accounting the number of dying
cgroups stabilizes at a relatively small number (~100, depends on memory
pressure and cgroup creation rate), and with kernel memory accounting it
grows pretty steadily up to several thousands.

Memory cgroups are quite complex and big objects (mostly due to percpu
stats), so it leads to noticeable memory losses.  Memory occupied by dying
cgroups is measured in hundreds of megabytes.  I've even seen a host with
more than 100Gb of memory wasted for dying cgroups.  It leads to a
degradation of performance with the uptime, and generally limits the usage
of cgroups.

My previous attempt [3] to fix the problem by applying extra pressure on
slab shrinker lists caused a regressions with xfs and ext4, and has been
reverted [4].  The following attempts to find the right balance [5, 6]
were not successful.

So instead of trying to find a maybe non-existing balance, let's do
reparent accounted slab caches to the parent cgroup on cgroup removal.

# Implementation approach

There is however a significant problem with reparenting of slab memory:
there is no list of charged pages.  Some of them are in shrinker lists,
but not all.  Introducing of a new list is really not an option.

But fortunately there is a way forward: every slab page has a stable
pointer to the corresponding kmem_cache.  So the idea is to reparent
kmem_caches instead of slab pages.

It's actually simpler and cheaper, but requires some underlying changes:
1) Make kmem_caches to hold a single reference to the memory cgroup,
   instead of a separate reference per every slab page.
2) Stop setting page->mem_cgroup pointer for memcg slab pages and use
   page->kmem_cache->memcg indirection instead. It's used only on
   slab page release, so performance overhead shouldn't be a big issue.
3) Introduce a refcounter for non-root slab caches. It's required to
   be able to destroy kmem_caches when they become empty and release
   the associated memory cgroup.

There is a bonus: currently we release all memcg kmem_caches all together
with the memory cgroup itself.  This patchset allows individual
kmem_caches to be released as soon as they become inactive and free.

Some additional implementation details are provided in corresponding
commit messages.

# Results

Below is the average number of dying cgroups on two groups of our
production hosts.  They do run some sort of web frontend workload, the
memory pressure is moderate.  As we can see, with the kernel memory
reparenting the number stabilizes in 60s range; however with the original
version it grows almost linearly and doesn't show any signs of plateauing.
The difference in slab and percpu usage between patched and unpatched
versions also grows linearly.  In 7 days it exceeded 200Mb.

day           0    1    2    3    4    5    6    7
original     56  362  628  752 1070 1250 1490 1560
patched      23   46   51   55   60   57   67   69
mem diff(Mb) 22   74  123  152  164  182  214  241

# Links

[1]: commit 68600f62 ("mm: don't miss the last page because of round-off error")
[2]: commit 9b6f7e16 ("mm: rework memcg kernel stack accounting")
[3]: commit 172b06c3 ("mm: slowly shrink slabs with a relatively small number of objects")
[4]: commit a9a238e8 ("Revert "mm: slowly shrink slabs with a relatively small number of objects")
[5]: https://lkml.org/lkml/2019/1/28/1865
[6]: https://marc.info/?l=linux-mm&m=155064763626437&w=2

This patch (of 10):

Initialize kmem_cache->memcg_params.memcg pointer in memcg_link_cache()
rather than in init_memcg_params().

Once kmem_cache will hold a reference to the memory cgroup, it will
simplify the refcounting.

For non-root kmem_caches memcg_link_cache() is always called before the
kmem_cache becomes visible to a user, so it's safe.

Link: http://lkml.kernel.org/r/20190611231813.3148843-2-guro@fb.comSigned-off-by: NRoman Gushchin <guro@fb.com>
Reviewed-by: NShakeel Butt <shakeelb@google.com>
Acked-by: NVladimir Davydov <vdavydov.dev@gmail.com>
Acked-by: NJohannes Weiner <hannes@cmpxchg.org>
Cc: Waiman Long <longman@redhat.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Andrei Vagin <avagin@gmail.com>
Cc: Qian Cai <cai@lca.pw>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

ksize() has been unconditionally unpoisoning the whole shadow memory
region associated with an allocation.  This can lead to various undetected
bugs, for example, double-kzfree().

Specifically, kzfree() uses ksize() to determine the actual allocation
size, and subsequently zeroes the memory.  Since ksize() used to just
unpoison the whole shadow memory region, no invalid free was detected.

This patch addresses this as follows:

1. Add a check in ksize(), and only then unpoison the memory region.

2. Preserve kasan_unpoison_slab() semantics by explicitly unpoisoning
   the shadow memory region using the size obtained from __ksize().

Tested:
1. With SLAB allocator: a) normal boot without warnings; b) verified the
   added double-kzfree() is detected.
2. With SLUB allocator: a) normal boot without warnings; b) verified the
   added double-kzfree() is detected.

[elver@google.com: s/BUG_ON/WARN_ON_ONCE/, per Kees]
  Link: http://lkml.kernel.org/r/20190627094445.216365-6-elver@google.com
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=199359
Link: http://lkml.kernel.org/r/20190626142014.141844-6-elver@google.comSigned-off-by: NMarco Elver <elver@google.com>
Acked-by: NKees Cook <keescook@chromium.org>
Reviewed-by: NAndrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Konovalov <andreyknvl@google.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

This refactors common code of ksize() between the various allocators into
slab_common.c: __ksize() is the allocator-specific implementation without
instrumentation, whereas ksize() includes the required KASAN logic.

Link: http://lkml.kernel.org/r/20190626142014.141844-5-elver@google.comSigned-off-by: NMarco Elver <elver@google.com>
Acked-by: NChristoph Lameter <cl@linux.com>
Reviewed-by: NAndrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Konovalov <andreyknvl@google.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Kees Cook <keescook@chromium.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Patch series "iommu/io-pgtable-arm-v7s: Use DMA32 zone for page tables",
v6.

This is a followup to the discussion in [1], [2].

IOMMUs using ARMv7 short-descriptor format require page tables (level 1
and 2) to be allocated within the first 4GB of RAM, even on 64-bit
systems.

For L1 tables that are bigger than a page, we can just use
__get_free_pages with GFP_DMA32 (on arm64 systems only, arm would still
use GFP_DMA).

For L2 tables that only take 1KB, it would be a waste to allocate a full
page, so we considered 3 approaches:
 1. This series, adding support for GFP_DMA32 slab caches.
 2. genalloc, which requires pre-allocating the maximum number of L2 page
    tables (4096, so 4MB of memory).
 3. page_frag, which is not very memory-efficient as it is unable to reuse
    freed fragments until the whole page is freed. [3]

This series is the most memory-efficient approach.

stable@ note:
  We confirmed that this is a regression, and IOMMU errors happen on 4.19
  and linux-next/master on MT8173 (elm, Acer Chromebook R13). The issue
  most likely starts from commit ad67f5a6 ("arm64: replace ZONE_DMA
  with ZONE_DMA32"), i.e. 4.15, and presumably breaks a number of Mediatek
  platforms (and maybe others?).

[1] https://lists.linuxfoundation.org/pipermail/iommu/2018-November/030876.html
[2] https://lists.linuxfoundation.org/pipermail/iommu/2018-December/031696.html
[3] https://patchwork.codeaurora.org/patch/671639/

This patch (of 3):

IOMMUs using ARMv7 short-descriptor format require page tables to be
allocated within the first 4GB of RAM, even on 64-bit systems.  On arm64,
this is done by passing GFP_DMA32 flag to memory allocation functions.

For IOMMU L2 tables that only take 1KB, it would be a waste to allocate
a full page using get_free_pages, so we considered 3 approaches:
 1. This patch, adding support for GFP_DMA32 slab caches.
 2. genalloc, which requires pre-allocating the maximum number of L2
    page tables (4096, so 4MB of memory).
 3. page_frag, which is not very memory-efficient as it is unable
    to reuse freed fragments until the whole page is freed.

This change makes it possible to create a custom cache in DMA32 zone using
kmem_cache_create, then allocate memory using kmem_cache_alloc.

We do not create a DMA32 kmalloc cache array, as there are currently no
users of kmalloc(..., GFP_DMA32).  These calls will continue to trigger a
warning, as we keep GFP_DMA32 in GFP_SLAB_BUG_MASK.

This implies that calls to kmem_cache_*alloc on a SLAB_CACHE_DMA32
kmem_cache must _not_ use GFP_DMA32 (it is anyway redundant and
unnecessary).

Link: http://lkml.kernel.org/r/20181210011504.122604-2-drinkcat@chromium.orgSigned-off-by: NNicolas Boichat <drinkcat@chromium.org>
Acked-by: NVlastimil Babka <vbabka@suse.cz>
Acked-by: NWill Deacon <will.deacon@arm.com>
Cc: Robin Murphy <robin.murphy@arm.com>
Cc: Joerg Roedel <joro@8bytes.org>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Sasha Levin <Alexander.Levin@microsoft.com>
Cc: Huaisheng Ye <yehs1@lenovo.com>
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: Yong Wu <yong.wu@mediatek.com>
Cc: Matthias Brugger <matthias.bgg@gmail.com>
Cc: Tomasz Figa <tfiga@google.com>
Cc: Yingjoe Chen <yingjoe.chen@mediatek.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Hsin-Yi Wang <hsinyi@chromium.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Many kernel-doc comments in mm/ have the return value descriptions
either misformatted or omitted at all which makes kernel-doc script
unhappy:

$ make V=1 htmldocs
...
./mm/util.c:36: info: Scanning doc for kstrdup
./mm/util.c:41: warning: No description found for return value of 'kstrdup'
./mm/util.c:57: info: Scanning doc for kstrdup_const
./mm/util.c:66: warning: No description found for return value of 'kstrdup_const'
./mm/util.c:75: info: Scanning doc for kstrndup
./mm/util.c:83: warning: No description found for return value of 'kstrndup'
...

Fixing the formatting and adding the missing return value descriptions
eliminates ~100 such warnings.

Link: http://lkml.kernel.org/r/1549549644-4903-4-git-send-email-rppt@linux.ibm.comSigned-off-by: NMike Rapoport <rppt@linux.ibm.com>
Reviewed-by: NAndrew Morton <akpm@linux-foundation.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

This is the start of a series of patches similar to my earlier
DEFINE_MEMCG_MAX_OR_VAL work, but with less Macro Magic(tm).

There are a bunch of places we go from seq_file to mem_cgroup, which
currently requires manually getting the css, then getting the mem_cgroup
from the css.  It's in enough places now that having mem_cgroup_from_seq
makes sense (and also makes the next patch a bit nicer).

Link: http://lkml.kernel.org/r/20190124194050.GA31341@chrisdown.nameSigned-off-by: NChris Down <chris@chrisdown.name>
Acked-by: NJohannes Weiner <hannes@cmpxchg.org>
Acked-by: NMichal Hocko <mhocko@suse.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Roman Gushchin <guro@fb.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

kmemleak keeps two global variables, min_addr and max_addr, which store
the range of valid (encountered by kmemleak) pointer values, which it
later uses to speed up pointer lookup when scanning blocks.

With tagged pointers this range will get bigger than it needs to be.  This
patch makes kmemleak untag pointers before saving them to min_addr and
max_addr and when performing a lookup.

Link: http://lkml.kernel.org/r/16e887d442986ab87fe87a755815ad92fa431a5f.1550066133.git.andreyknvl@google.comSigned-off-by: NAndrey Konovalov <andreyknvl@google.com>
Tested-by: NQian Cai <cai@lca.pw>
Acked-by: NCatalin Marinas <catalin.marinas@arm.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Evgeniy Stepanov <eugenis@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Kostya Serebryany <kcc@google.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Vincenzo Frascino <vincenzo.frascino@arm.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Right now we call kmemleak hooks before assigning tags to pointers in
KASAN hooks.  As a result, when an objects gets allocated, kmemleak sees a
differently tagged pointer, compared to the one it sees when the object
gets freed.  Fix it by calling KASAN hooks before kmemleak's ones.

Link: http://lkml.kernel.org/r/cd825aa4897b0fc37d3316838993881daccbe9f5.1549921721.git.andreyknvl@google.comSigned-off-by: NAndrey Konovalov <andreyknvl@google.com>
Reported-by: NQian Cai <cai@lca.pw>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Evgeniy Stepanov <eugenis@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Kostya Serebryany <kcc@google.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Vincenzo Frascino <vincenzo.frascino@arm.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

WARN_ON() already contains an unlikely(), so it's not necessary to use
unlikely.

Also change WARN_ON() back to WARN_ON_ONCE() to avoid potentially
spamming dmesg with user-triggerable large allocations.

[akpm@linux-foundation.org: s/WARN_ON/WARN_ON_ONCE/, per Vlastimil]
Link: http://lkml.kernel.org/r/20181104125028.3572-1-tiny.windzz@gmail.comSigned-off-by: NYangtao Li <tiny.windzz@gmail.com>
Acked-by: NVlastimil Babka <vbabka@suse.cz>
Reviewed-by: NAndrew Morton <akpm@linux-foundation.org>
Acked-by: NDavid Rientjes <rientjes@google.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

The krealloc function checks where the same buffer was reused or a new one
allocated by comparing kernel pointers.  Tag-based KASAN changes memory
tag on the krealloc'ed chunk of memory and therefore also changes the
pointer tag of the returned pointer.  Therefore we need to perform
comparison on untagged (with tags reset) pointers to check whether it's
the same memory region or not.

Link: http://lkml.kernel.org/r/14f6190d7846186a3506cd66d82446646fe65090.1544099024.git.andreyknvl@google.comSigned-off-by: NAndrey Konovalov <andreyknvl@google.com>
Reviewed-by: NAndrey Ryabinin <aryabinin@virtuozzo.com>
Reviewed-by: NDmitry Vyukov <dvyukov@google.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Patch series "kasan: add software tag-based mode for arm64", v13.

This patchset adds a new software tag-based mode to KASAN [1].  (Initially
this mode was called KHWASAN, but it got renamed, see the naming rationale
at the end of this section).

The plan is to implement HWASan [2] for the kernel with the incentive,
that it's going to have comparable to KASAN performance, but in the same
time consume much less memory, trading that off for somewhat imprecise bug
detection and being supported only for arm64.

The underlying ideas of the approach used by software tag-based KASAN are:

1. By using the Top Byte Ignore (TBI) arm64 CPU feature, we can store
   pointer tags in the top byte of each kernel pointer.

2. Using shadow memory, we can store memory tags for each chunk of kernel
   memory.

3. On each memory allocation, we can generate a random tag, embed it into
   the returned pointer and set the memory tags that correspond to this
   chunk of memory to the same value.

4. By using compiler instrumentation, before each memory access we can add
   a check that the pointer tag matches the tag of the memory that is being
   accessed.

5. On a tag mismatch we report an error.

With this patchset the existing KASAN mode gets renamed to generic KASAN,
with the word "generic" meaning that the implementation can be supported
by any architecture as it is purely software.

The new mode this patchset adds is called software tag-based KASAN.  The
word "tag-based" refers to the fact that this mode uses tags embedded into
the top byte of kernel pointers and the TBI arm64 CPU feature that allows
to dereference such pointers.  The word "software" here means that shadow
memory manipulation and tag checking on pointer dereference is done in
software.  As it is the only tag-based implementation right now, "software
tag-based" KASAN is sometimes referred to as simply "tag-based" in this
patchset.

A potential expansion of this mode is a hardware tag-based mode, which
would use hardware memory tagging support (announced by Arm [3]) instead
of compiler instrumentation and manual shadow memory manipulation.

Same as generic KASAN, software tag-based KASAN is strictly a debugging
feature.

[1] https://www.kernel.org/doc/html/latest/dev-tools/kasan.html

[2] http://clang.llvm.org/docs/HardwareAssistedAddressSanitizerDesign.html

[3] https://community.arm.com/processors/b/blog/posts/arm-a-profile-architecture-2018-developments-armv85a

====== Rationale

On mobile devices generic KASAN's memory usage is significant problem.
One of the main reasons to have tag-based KASAN is to be able to perform a
similar set of checks as the generic one does, but with lower memory
requirements.

Comment from Vishwath Mohan <vishwath@google.com>:

I don't have data on-hand, but anecdotally both ASAN and KASAN have proven
problematic to enable for environments that don't tolerate the increased
memory pressure well.  This includes

(a) Low-memory form factors - Wear, TV, Things, lower-tier phones like Go,
(c) Connected components like Pixel's visual core [1].

These are both places I'd love to have a low(er) memory footprint option at
my disposal.

Comment from Evgenii Stepanov <eugenis@google.com>:

Looking at a live Android device under load, slab (according to
/proc/meminfo) + kernel stack take 8-10% available RAM (~350MB).  KASAN's
overhead of 2x - 3x on top of it is not insignificant.

Not having this overhead enables near-production use - ex.  running
KASAN/KHWASAN kernel on a personal, daily-use device to catch bugs that do
not reproduce in test configuration.  These are the ones that often cost
the most engineering time to track down.

CPU overhead is bad, but generally tolerable.  RAM is critical, in our
experience.  Once it gets low enough, OOM-killer makes your life
miserable.

[1] https://www.blog.google/products/pixel/pixel-visual-core-image-processing-and-machine-learning-pixel-2/

====== Technical details

Software tag-based KASAN mode is implemented in a very similar way to the
generic one. This patchset essentially does the following:

1. TCR_TBI1 is set to enable Top Byte Ignore.

2. Shadow memory is used (with a different scale, 1:16, so each shadow
   byte corresponds to 16 bytes of kernel memory) to store memory tags.

3. All slab objects are aligned to shadow scale, which is 16 bytes.

4. All pointers returned from the slab allocator are tagged with a random
   tag and the corresponding shadow memory is poisoned with the same value.

5. Compiler instrumentation is used to insert tag checks. Either by
   calling callbacks or by inlining them (CONFIG_KASAN_OUTLINE and
   CONFIG_KASAN_INLINE flags are reused).

6. When a tag mismatch is detected in callback instrumentation mode
   KASAN simply prints a bug report. In case of inline instrumentation,
   clang inserts a brk instruction, and KASAN has it's own brk handler,
   which reports the bug.

7. The memory in between slab objects is marked with a reserved tag, and
   acts as a redzone.

8. When a slab object is freed it's marked with a reserved tag.

Bug detection is imprecise for two reasons:

1. We won't catch some small out-of-bounds accesses, that fall into the
   same shadow cell, as the last byte of a slab object.

2. We only have 1 byte to store tags, which means we have a 1/256
   probability of a tag match for an incorrect access (actually even
   slightly less due to reserved tag values).

Despite that there's a particular type of bugs that tag-based KASAN can
detect compared to generic KASAN: use-after-free after the object has been
allocated by someone else.

====== Testing

Some kernel developers voiced a concern that changing the top byte of
kernel pointers may lead to subtle bugs that are difficult to discover.
To address this concern deliberate testing has been performed.

It doesn't seem feasible to do some kind of static checking to find
potential issues with pointer tagging, so a dynamic approach was taken.
All pointer comparisons/subtractions have been instrumented in an LLVM
compiler pass and a kernel module that would print a bug report whenever
two pointers with different tags are being compared/subtracted (ignoring
comparisons with NULL pointers and with pointers obtained by casting an
error code to a pointer type) has been used.  Then the kernel has been
booted in QEMU and on an Odroid C2 board and syzkaller has been run.

This yielded the following results.

The two places that look interesting are:

is_vmalloc_addr in include/linux/mm.h
is_kernel_rodata in mm/util.c

Here we compare a pointer with some fixed untagged values to make sure
that the pointer lies in a particular part of the kernel address space.
Since tag-based KASAN doesn't add tags to pointers that belong to rodata
or vmalloc regions, this should work as is.  To make sure debug checks to
those two functions that check that the result doesn't change whether we
operate on pointers with or without untagging has been added.

A few other cases that don't look that interesting:

Comparing pointers to achieve unique sorting order of pointee objects
(e.g. sorting locks addresses before performing a double lock):

tty_ldisc_lock_pair_timeout in drivers/tty/tty_ldisc.c
pipe_double_lock in fs/pipe.c
unix_state_double_lock in net/unix/af_unix.c
lock_two_nondirectories in fs/inode.c
mutex_lock_double in kernel/events/core.c

ep_cmp_ffd in fs/eventpoll.c
fsnotify_compare_groups fs/notify/mark.c

Nothing needs to be done here, since the tags embedded into pointers
don't change, so the sorting order would still be unique.

Checks that a pointer belongs to some particular allocation:

is_sibling_entry in lib/radix-tree.c
object_is_on_stack in include/linux/sched/task_stack.h

Nothing needs to be done here either, since two pointers can only belong
to the same allocation if they have the same tag.

Overall, since the kernel boots and works, there are no critical bugs.
As for the rest, the traditional kernel testing way (use until fails) is
the only one that looks feasible.

Another point here is that tag-based KASAN is available under a separate
config option that needs to be deliberately enabled. Even though it might
be used in a "near-production" environment to find bugs that are not found
during fuzzing or running tests, it is still a debug tool.

====== Benchmarks

The following numbers were collected on Odroid C2 board. Both generic and
tag-based KASAN were used in inline instrumentation mode.

Boot time [1]:
* ~1.7 sec for clean kernel
* ~5.0 sec for generic KASAN
* ~5.0 sec for tag-based KASAN

Network performance [2]:
* 8.33 Gbits/sec for clean kernel
* 3.17 Gbits/sec for generic KASAN
* 2.85 Gbits/sec for tag-based KASAN

Slab memory usage after boot [3]:
* ~40 kb for clean kernel
* ~105 kb (~260% overhead) for generic KASAN
* ~47 kb (~20% overhead) for tag-based KASAN

KASAN memory overhead consists of three main parts:
1. Increased slab memory usage due to redzones.
2. Shadow memory (the whole reserved once during boot).
3. Quaratine (grows gradually until some preset limit; the more the limit,
   the more the chance to detect a use-after-free).

Comparing tag-based vs generic KASAN for each of these points:
1. 20% vs 260% overhead.
2. 1/16th vs 1/8th of physical memory.
3. Tag-based KASAN doesn't require quarantine.

[1] Time before the ext4 driver is initialized.
[2] Measured as `iperf -s & iperf -c 127.0.0.1 -t 30`.
[3] Measured as `cat /proc/meminfo | grep Slab`.

====== Some notes

A few notes:

1. The patchset can be found here:
   https://github.com/xairy/kasan-prototype/tree/khwasan

2. Building requires a recent Clang version (7.0.0 or later).

3. Stack instrumentation is not supported yet and will be added later.

This patch (of 25):

Tag-based KASAN changes the value of the top byte of pointers returned
from the kernel allocation functions (such as kmalloc).  This patch
updates KASAN hooks signatures and their usage in SLAB and SLUB code to
reflect that.

Link: http://lkml.kernel.org/r/aec2b5e3973781ff8a6bb6760f8543643202c451.1544099024.git.andreyknvl@google.comSigned-off-by: NAndrey Konovalov <andreyknvl@google.com>
Reviewed-by: NAndrey Ryabinin <aryabinin@virtuozzo.com>
Reviewed-by: NDmitry Vyukov <dvyukov@google.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Add the description for kmem_cache_create, fixup the return value paragraph
and make both kmem_cache_create and add the second '*' to the comment
opening.
Signed-off-by: NMike Rapoport <rppt@linux.ibm.com>
Signed-off-by: NJonathan Corbet <corbet@lwn.net>

Now that synchronize_rcu() waits for preempt-disable regions of code
as well as RCU read-side critical sections, synchronize_sched() can be
replaced by synchronize_rcu().  This commit therefore makes this change.
Signed-off-by: NPaul E. McKenney <paulmck@linux.ibm.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: <linux-mm@kvack.org>

Kmalloc cache names can get quite long for large object sizes, when the
sizes are expressed in bytes.  Use 'k' and 'M' prefixes to make the names
as short as possible e.g.  in /proc/slabinfo.  This works, as we mostly
use power-of-two sizes, with exceptions only below 1k.

Example: 'kmalloc-4194304' becomes 'kmalloc-4M'

Link: http://lkml.kernel.org/r/20180731090649.16028-7-vbabka@suse.czSuggested-by: NMatthew Wilcox <willy@infradead.org>
Signed-off-by: NVlastimil Babka <vbabka@suse.cz>
Acked-by: NMel Gorman <mgorman@techsingularity.net>
Acked-by: NChristoph Lameter <cl@linux.com>
Acked-by: NRoman Gushchin <guro@fb.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Laura Abbott <labbott@redhat.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: Vijayanand Jitta <vjitta@codeaurora.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Kmem caches can be created with a SLAB_RECLAIM_ACCOUNT flag, which
indicates they contain objects which can be reclaimed under memory
pressure (typically through a shrinker).  This makes the slab pages
accounted as NR_SLAB_RECLAIMABLE in vmstat, which is reflected also the
MemAvailable meminfo counter and in overcommit decisions.  The slab pages
are also allocated with __GFP_RECLAIMABLE, which is good for
anti-fragmentation through grouping pages by mobility.

The generic kmalloc-X caches are created without this flag, but sometimes
are used also for objects that can be reclaimed, which due to varying size
cannot have a dedicated kmem cache with SLAB_RECLAIM_ACCOUNT flag.  A
prominent example are dcache external names, which prompted the creation
of a new, manually managed vmstat counter NR_INDIRECTLY_RECLAIMABLE_BYTES
in commit f1782c9b ("dcache: account external names as indirectly
reclaimable memory").

To better handle this and any other similar cases, this patch introduces
SLAB_RECLAIM_ACCOUNT variants of kmalloc caches, named kmalloc-rcl-X.
They are used whenever the kmalloc() call passes __GFP_RECLAIMABLE among
gfp flags.  They are added to the kmalloc_caches array as a new type.
Allocations with both __GFP_DMA and __GFP_RECLAIMABLE will use a dma type
cache.

This change only applies to SLAB and SLUB, not SLOB.  This is fine, since
SLOB's target are tiny system and this patch does add some overhead of
kmem management objects.

Link: http://lkml.kernel.org/r/20180731090649.16028-3-vbabka@suse.czSigned-off-by: NVlastimil Babka <vbabka@suse.cz>
Acked-by: NMel Gorman <mgorman@techsingularity.net>
Acked-by: NChristoph Lameter <cl@linux.com>
Acked-by: NRoman Gushchin <guro@fb.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Laura Abbott <labbott@redhat.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: Vijayanand Jitta <vjitta@codeaurora.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Patch series "kmalloc-reclaimable caches", v4.

As discussed at LSF/MM [1] here's a patchset that introduces
kmalloc-reclaimable caches (more details in the second patch) and uses
them for dcache external names.  That allows us to repurpose the
NR_INDIRECTLY_RECLAIMABLE_BYTES counter later in the series.

With patch 3/6, dcache external names are allocated from kmalloc-rcl-*
caches, eliminating the need for manual accounting.  More importantly, it
also ensures the reclaimable kmalloc allocations are grouped in pages
separate from the regular kmalloc allocations.  The need for proper
accounting of dcache external names has shown it's easy for misbehaving
process to allocate lots of them, causing premature OOMs.  Without the
added grouping, it's likely that a similar workload can interleave the
dcache external names allocations with regular kmalloc allocations (note:
I haven't searched myself for an example of such regular kmalloc
allocation, but I would be very surprised if there wasn't some).  A
pathological case would be e.g.  one 64byte regular allocations with 63
external dcache names in a page (64x64=4096), which means the page is not
freed even after reclaiming after all dcache names, and the process can
thus "steal" the whole page with single 64byte allocation.

If other kmalloc users similar to dcache external names become identified,
they can also benefit from the new functionality simply by adding
__GFP_RECLAIMABLE to the kmalloc calls.

Side benefits of the patchset (that could be also merged separately)
include removed branch for detecting __GFP_DMA kmalloc(), and shortening
kmalloc cache names in /proc/slabinfo output.  The latter is potentially
an ABI break in case there are tools parsing the names and expecting the
values to be in bytes.

This is how /proc/slabinfo looks like after booting in virtme:

...
kmalloc-rcl-4M         0      0 4194304    1 1024 : tunables    1    1    0 : slabdata      0      0      0
...
kmalloc-rcl-96         7     32    128   32    1 : tunables  120   60    8 : slabdata      1      1      0
kmalloc-rcl-64        25    128     64   64    1 : tunables  120   60    8 : slabdata      2      2      0
kmalloc-rcl-32         0      0     32  124    1 : tunables  120   60    8 : slabdata      0      0      0
kmalloc-4M             0      0 4194304    1 1024 : tunables    1    1    0 : slabdata      0      0      0
kmalloc-2M             0      0 2097152    1  512 : tunables    1    1    0 : slabdata      0      0      0
kmalloc-1M             0      0 1048576    1  256 : tunables    1    1    0 : slabdata      0      0      0
...

/proc/vmstat with renamed nr_indirectly_reclaimable_bytes counter:

...
nr_slab_reclaimable 2817
nr_slab_unreclaimable 1781
...
nr_kernel_misc_reclaimable 0
...

/proc/meminfo with new KReclaimable counter:

...
Shmem:               564 kB
KReclaimable:      11260 kB
Slab:              18368 kB
SReclaimable:      11260 kB
SUnreclaim:         7108 kB
KernelStack:        1248 kB
...

This patch (of 6):

The kmalloc caches currently mainain separate (optional) array
kmalloc_dma_caches for __GFP_DMA allocations.  There are tests for
__GFP_DMA in the allocation hotpaths.  We can avoid the branches by
combining kmalloc_caches and kmalloc_dma_caches into a single
two-dimensional array where the outer dimension is cache "type".  This
will also allow to add kmalloc-reclaimable caches as a third type.

Link: http://lkml.kernel.org/r/20180731090649.16028-2-vbabka@suse.czSigned-off-by: NVlastimil Babka <vbabka@suse.cz>
Acked-by: NMel Gorman <mgorman@techsingularity.net>
Acked-by: NChristoph Lameter <cl@linux.com>
Acked-by: NRoman Gushchin <guro@fb.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Laura Abbott <labbott@redhat.com>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: Vijayanand Jitta <vjitta@codeaurora.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Slub does not call kmalloc_slab() for sizes > KMALLOC_MAX_CACHE_SIZE,
instead it falls back to kmalloc_large().

For slab KMALLOC_MAX_CACHE_SIZE == KMALLOC_MAX_SIZE and it calls
kmalloc_slab() for all allocations relying on NULL return value for
over-sized allocations.

This inconsistency leads to unwanted warnings from kmalloc_slab() for
over-sized allocations for slab.  Returning NULL for failed allocations is
the expected behavior.

Make slub and slab code consistent by checking size >
KMALLOC_MAX_CACHE_SIZE in slab before calling kmalloc_slab().

While we are here also fix the check in kmalloc_slab().  We should check
against KMALLOC_MAX_CACHE_SIZE rather than KMALLOC_MAX_SIZE.  It all kinda
worked because for slab the constants are the same, and slub always checks
the size against KMALLOC_MAX_CACHE_SIZE before kmalloc_slab().  But if we
get there with size > KMALLOC_MAX_CACHE_SIZE anyhow bad things will
happen.  For example, in case of a newly introduced bug in slub code.

Also move the check in kmalloc_slab() from function entry to the size >
192 case.  This partially compensates for the additional check in slab
code and makes slub code a bit faster (at least theoretically).

Also drop __GFP_NOWARN in the warning check.  This warning means a bug in
slab code itself, user-passed flags have nothing to do with it.

Nothing of this affects slob.

Link: http://lkml.kernel.org/r/20180927171502.226522-1-dvyukov@gmail.comSigned-off-by: NDmitry Vyukov <dvyukov@google.com>
Reported-by: syzbot+87829a10073277282ad1@syzkaller.appspotmail.com
Reported-by: syzbot+ef4e8fc3a06e9019bb40@syzkaller.appspotmail.com
Reported-by: syzbot+6e438f4036df52cbb863@syzkaller.appspotmail.com
Reported-by: syzbot+8574471d8734457d98aa@syzkaller.appspotmail.com
Reported-by: syzbot+af1504df0807a083dbd9@syzkaller.appspotmail.com
Acked-by: NChristoph Lameter <cl@linux.com>
Acked-by: NVlastimil Babka <vbabka@suse.cz>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Introduce new config option, which is used to replace repeating
CONFIG_MEMCG && !CONFIG_SLOB pattern.  Next patches add a little more
memcg+kmem related code, so let's keep the defines more clearly.

Link: http://lkml.kernel.org/r/153063053670.1818.15013136946600481138.stgit@localhost.localdomainSigned-off-by: NKirill Tkhai <ktkhai@virtuozzo.com>
Acked-by: NVladimir Davydov <vdavydov.dev@gmail.com>
Tested-by: NShakeel Butt <shakeelb@google.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Guenter Roeck <linux@roeck-us.net>
Cc: "Huang, Ying" <ying.huang@intel.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Josef Bacik <jbacik@fb.com>
Cc: Li RongQing <lirongqing@baidu.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Matthias Kaehlcke <mka@chromium.org>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Philippe Ombredanne <pombredanne@nexb.com>
Cc: Roman Gushchin <guro@fb.com>
Cc: Sahitya Tummala <stummala@codeaurora.org>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Waiman Long <longman@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

In kernel 4.17 I removed some code from dm-bufio that did slab cache
merging (commit 21bb1327: "dm bufio: remove code that merges slab
caches") - both slab and slub support merging caches with identical
attributes, so dm-bufio now just calls kmem_cache_create and relies on
implicit merging.

This uncovered a bug in the slub subsystem - if we delete a cache and
immediatelly create another cache with the same attributes, it fails
because of duplicate filename in /sys/kernel/slab/.  The slub subsystem
offloads freeing the cache to a workqueue - and if we create the new
cache before the workqueue runs, it complains because of duplicate
filename in sysfs.

This patch fixes the bug by moving the call of kobject_del from
sysfs_slab_remove_workfn to shutdown_cache.  kobject_del must be called
while we hold slab_mutex - so that the sysfs entry is deleted before a
cache with the same attributes could be created.

Running device-mapper-test-suite with:

  dmtest run --suite thin-provisioning -n /commit_failure_causes_fallback/

triggered:

  Buffer I/O error on dev dm-0, logical block 1572848, async page read
  device-mapper: thin: 253:1: metadata operation 'dm_pool_alloc_data_block' failed: error = -5
  device-mapper: thin: 253:1: aborting current metadata transaction
  sysfs: cannot create duplicate filename '/kernel/slab/:a-0000144'
  CPU: 2 PID: 1037 Comm: kworker/u48:1 Not tainted 4.17.0.snitm+ #25
  Hardware name: Supermicro SYS-1029P-WTR/X11DDW-L, BIOS 2.0a 12/06/2017
  Workqueue: dm-thin do_worker [dm_thin_pool]
  Call Trace:
   dump_stack+0x5a/0x73
   sysfs_warn_dup+0x58/0x70
   sysfs_create_dir_ns+0x77/0x80
   kobject_add_internal+0xba/0x2e0
   kobject_init_and_add+0x70/0xb0
   sysfs_slab_add+0xb1/0x250
   __kmem_cache_create+0x116/0x150
   create_cache+0xd9/0x1f0
   kmem_cache_create_usercopy+0x1c1/0x250
   kmem_cache_create+0x18/0x20
   dm_bufio_client_create+0x1ae/0x410 [dm_bufio]
   dm_block_manager_create+0x5e/0x90 [dm_persistent_data]
   __create_persistent_data_objects+0x38/0x940 [dm_thin_pool]
   dm_pool_abort_metadata+0x64/0x90 [dm_thin_pool]
   metadata_operation_failed+0x59/0x100 [dm_thin_pool]
   alloc_data_block.isra.53+0x86/0x180 [dm_thin_pool]
   process_cell+0x2a3/0x550 [dm_thin_pool]
   do_worker+0x28d/0x8f0 [dm_thin_pool]
   process_one_work+0x171/0x370
   worker_thread+0x49/0x3f0
   kthread+0xf8/0x130
   ret_from_fork+0x35/0x40
  kobject_add_internal failed for :a-0000144 with -EEXIST, don't try to register things with the same name in the same directory.
  kmem_cache_create(dm_bufio_buffer-16) failed with error -17

Link: http://lkml.kernel.org/r/alpine.LRH.2.02.1806151817130.6333@file01.intranet.prod.int.rdu2.redhat.comSigned-off-by: NMikulas Patocka <mpatocka@redhat.com>
Reported-by: NMike Snitzer <snitzer@redhat.com>
Tested-by: NMike Snitzer <snitzer@redhat.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

mm/*.c files use symbolic and octal styles for permissions.

Using octal and not symbolic permissions is preferred by many as more
readable.

https://lkml.org/lkml/2016/8/2/1945

Prefer the direct use of octal for permissions.

Done using
$ scripts/checkpatch.pl -f --types=SYMBOLIC_PERMS --fix-inplace mm/*.c
and some typing.

Before:	 $ git grep -P -w "0[0-7]{3,3}" mm | wc -l
44
After:	 $ git grep -P -w "0[0-7]{3,3}" mm | wc -l
86

Miscellanea:

o Whitespace neatening around these conversions.

Link: http://lkml.kernel.org/r/2e032ef111eebcd4c5952bae86763b541d373469.1522102887.git.joe@perches.comSigned-off-by: NJoe Perches <joe@perches.com>
Acked-by: NDavid Rientjes <rientjes@google.com>
Acked-by: NMichal Hocko <mhocko@suse.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

The memcg kmem cache creation and deactivation (SLUB only) is
asynchronous.  If a root kmem cache is destroyed whose memcg cache is in
the process of creation or deactivation, the kernel may crash.

Example of one such crash:
	general protection fault: 0000 [#1] SMP PTI
	CPU: 1 PID: 1721 Comm: kworker/14:1 Not tainted 4.17.0-smp
	...
	Workqueue: memcg_kmem_cache kmemcg_deactivate_workfn
	RIP: 0010:has_cpu_slab
	...
	Call Trace:
	? on_each_cpu_cond
	__kmem_cache_shrink
	kmemcg_cache_deact_after_rcu
	kmemcg_deactivate_workfn
	process_one_work
	worker_thread
	kthread
	ret_from_fork+0x35/0x40

To fix this race, on root kmem cache destruction, mark the cache as
dying and flush the workqueue used for memcg kmem cache creation and
deactivation.  SLUB's memcg kmem cache deactivation also includes RCU
callback and thus make sure all previous registered RCU callbacks have
completed as well.

[shakeelb@google.com: handle the RCU callbacks for SLUB deactivation]
  Link: http://lkml.kernel.org/r/20180611192951.195727-1-shakeelb@google.com
[shakeelb@google.com: add more documentation, rename fields for readability]
  Link: http://lkml.kernel.org/r/20180522201336.196994-1-shakeelb@google.com
[akpm@linux-foundation.org: fix build, per Shakeel]
[shakeelb@google.com: v3.  Instead of refcount, flush the workqueue]
  Link: http://lkml.kernel.org/r/20180530001204.183758-1-shakeelb@google.com
Link: http://lkml.kernel.org/r/20180521174116.171846-1-shakeelb@google.comSigned-off-by: NShakeel Butt <shakeelb@google.com>
Acked-by: NVladimir Davydov <vdavydov.dev@gmail.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Greg Thelen <gthelen@google.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

should_failslab() is a convenient function to hook into for directed
error injection into kmalloc().  However, it is only available if a
config flag is set.

The following BCC script, for example, fails kmalloc() calls after a
btrfs umount:

    from bcc import BPF

    prog = r"""
    BPF_HASH(flag);

    #include <linux/mm.h>

    int kprobe__btrfs_close_devices(void *ctx) {
            u64 key = 1;
            flag.update(&key, &key);
            return 0;
    }

    int kprobe__should_failslab(struct pt_regs *ctx) {
            u64 key = 1;
            u64 *res;
            res = flag.lookup(&key);
            if (res != 0) {
                bpf_override_return(ctx, -ENOMEM);
            }
            return 0;
    }
    """
    b = BPF(text=prog)

    while 1:
        b.kprobe_poll()

This patch refactors the should_failslab implementation so that the
function is always available for error injection, independent of flags.

This change would be similar in nature to commit f5490d3ec921 ("block:
Add should_fail_bio() for bpf error injection").

Link: http://lkml.kernel.org/r/20180222020320.6944-1-hmclauchlan@fb.comSigned-off-by: NHoward McLauchlan <hmclauchlan@fb.com>
Reviewed-by: NAndrew Morton <akpm@linux-foundation.org>
Cc: Akinobu Mita <akinobu.mita@gmail.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Josef Bacik <jbacik@fb.com>
Cc: Johannes Weiner <jweiner@fb.com>
Cc: Alexei Starovoitov <ast@fb.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Since commit db265eca ("mm/sl[aou]b: Move duping of slab name to
slab_common.c"), the kernel always duplicates the slab cache name when
creating a slab cache, so the test if the slab name is accessible is
useless.

Link: http://lkml.kernel.org/r/alpine.LRH.2.02.1803231133310.22626@file01.intranet.prod.int.rdu2.redhat.comSigned-off-by: NMikulas Patocka <mpatocka@redhat.com>
Acked-by: NChristoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

I have noticed on debug kernel with SLAB, the size of some non-root
slabs were larger than their corresponding root slabs.

e.g. for radix_tree_node:
  $cat /proc/slabinfo | grep radix
  name     <active_objs> <num_objs> <objsize> <objperslab> <pagesperslab> ...
  radix_tree_node 15052    15075      4096         1             1 ...

  $cat /cgroup/memory/temp/memory.kmem.slabinfo | grep radix
  name     <active_objs> <num_objs> <objsize> <objperslab> <pagesperslab> ...
  radix_tree_node 1581      158       4120         1             2 ...

However for SLUB in debug kernel, the sizes were same.  On further
inspection it is found that SLUB always use kmem_cache.object_size to
measure the kmem_cache.size while SLAB use the given kmem_cache.size.
In the debug kernel the slab's size can be larger than its object_size.
Thus in the creation of non-root slab, the SLAB uses the root's size as
base to calculate the non-root slab's size and thus non-root slab's size
can be larger than the root slab's size.  For SLUB, the non-root slab's
size is measured based on the root's object_size and thus the size will
remain same for root and non-root slab.

This patch makes slab's object_size the default base to measure the
slab's size.

Link: http://lkml.kernel.org/r/20180313165428.58699-1-shakeelb@google.com
Fixes: 794b1248 ("memcg, slab: separate memcg vs root cache creation paths")
Signed-off-by: NShakeel Butt <shakeelb@google.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

SLAB doesn't support 4GB+ of objects per slab, therefore randomization
doesn't need size_t.

Link: http://lkml.kernel.org/r/20180305200730.15812-25-adobriyan@gmail.comSigned-off-by: NAlexey Dobriyan <adobriyan@gmail.com>
Acked-by: NChristoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

If kmem case sizes are 32-bit, then usecopy region should be too.

Link: http://lkml.kernel.org/r/20180305200730.15812-21-adobriyan@gmail.comSigned-off-by: NAlexey Dobriyan <adobriyan@gmail.com>
Cc: David Miller <davem@davemloft.net>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Linux doesn't support negative length objects.

Link: http://lkml.kernel.org/r/20180305200730.15812-17-adobriyan@gmail.comSigned-off-by: NAlexey Dobriyan <adobriyan@gmail.com>
Acked-by: NChristoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

size_index_elem() always works with small sizes (kmalloc caches are
32-bit) and returns small indexes.

Link: http://lkml.kernel.org/r/20180305200730.15812-8-adobriyan@gmail.comSigned-off-by: NAlexey Dobriyan <adobriyan@gmail.com>
Acked-by: NChristoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

All those small numbers are reverse indexes into kmalloc caches array
and can't be negative.

On x86_64 "unsigned int = fls()" can drop CDQE instruction:

	add/remove: 0/0 grow/shrink: 0/1 up/down: 0/-2 (-2)
	Function                                     old     new   delta
	kmalloc_slab                                 101      99      -2

Link: http://lkml.kernel.org/r/20180305200730.15812-7-adobriyan@gmail.comSigned-off-by: NAlexey Dobriyan <adobriyan@gmail.com>
Acked-by: NChristoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

struct kmem_cache::size and ::align were always 32-bit.

Out of curiosity I created 4GB kmem_cache, it oopsed with division by 0.
kmem_cache_create(1UL<<32+1) created 1-byte cache as expected.

size_t doesn't work and never did.

Link: http://lkml.kernel.org/r/20180305200730.15812-6-adobriyan@gmail.comSigned-off-by: NAlexey Dobriyan <adobriyan@gmail.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

struct kmem_cache::size has always been "int", all those
"size_t size" are fake.

Link: http://lkml.kernel.org/r/20180305200730.15812-5-adobriyan@gmail.comSigned-off-by: NAlexey Dobriyan <adobriyan@gmail.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Matthew Wilcox <willy@infradead.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

KMALLOC_MAX_CACHE_SIZE is 32-bit so is the largest kmalloc cache size.

Christoph said:
:
: Ok SLABs maximum allocation size is limited to 32M (see
: include/linux/slab.h:
:
: #define KMALLOC_SHIFT_HIGH      ((MAX_ORDER + PAGE_SHIFT - 1) <= 25 ? \
:                                 (MAX_ORDER + PAGE_SHIFT - 1) : 25)
:
: And SLUB/SLOB pass all larger requests to the page allocator anyways.

Link: http://lkml.kernel.org/r/20180305200730.15812-4-adobriyan@gmail.comSigned-off-by: NAlexey Dobriyan <adobriyan@gmail.com>
Acked-by: NChristoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

kmalloc_size() derives size of kmalloc cache from internal index, which
can't be negative.

Propagate unsignedness a bit.

Link: http://lkml.kernel.org/r/20180305200730.15812-3-adobriyan@gmail.comSigned-off-by: NAlexey Dobriyan <adobriyan@gmail.com>
Acked-by: NChristoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>