The move precharge function does some baroque things: it tries raw
res_counter charging of the entire amount first, and then falls back to
a loop of one-by-one charges, with checks for pending signals and
cond_resched() batching.

Just use mem_cgroup_try_charge() without __GFP_WAIT for the first bulk
charge attempt.  In the one-by-one loop, remove the signal check (this
is already checked in try_charge), and simply call cond_resched() after
every charge - it's not that expensive.
Signed-off-by: NJohannes Weiner <hannes@cmpxchg.org>
Acked-by: NMichal Hocko <mhocko@suse.cz>
Cc: Hugh Dickins <hughd@google.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Vladimir Davydov <vdavydov@parallels.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

For the page allocator, __GFP_NORETRY implies that no OOM should be
triggered, whereas memcg has an explicit parameter to disable OOM.

The only callsites that want OOM disabled are THP charges and charge
moving.  THP already uses __GFP_NORETRY and charge moving can use it as
well - one full reclaim cycle should be plenty.  Switch it over, then
remove the OOM parameter.
Signed-off-by: NJohannes Weiner <hannes@cmpxchg.org>
Signed-off-by: NMichal Hocko <mhocko@suse.cz>
Cc: Hugh Dickins <hughd@google.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Vladimir Davydov <vdavydov@parallels.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

There is no reason why oom-disabled and __GFP_NOFAIL charges should try
to reclaim only once when every other charge tries several times before
giving up.  Make them all retry the same number of times.
Signed-off-by: NJohannes Weiner <hannes@cmpxchg.org>
Acked-by: NMichal Hocko <mhocko@suse.cz>
Cc: Hugh Dickins <hughd@google.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Vladimir Davydov <vdavydov@parallels.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Currently, __GFP_NORETRY tries charging once and gives up before even
trying to reclaim.  Bring the behavior on par with the page allocator
and reclaim at least once before giving up.
Signed-off-by: NJohannes Weiner <hannes@cmpxchg.org>
Acked-by: NMichal Hocko <mhocko@suse.cz>
Cc: Hugh Dickins <hughd@google.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Vladimir Davydov <vdavydov@parallels.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

The charging path currently starts out with OOM condition checks when
OOM is the rarest possible case.

Rearrange this code to run OOM/task dying checks only after trying the
percpu charge and the res_counter charge and bail out before entering
reclaim.  Attempting a charge does not hurt an (oom-)killed task as much
as every charge attempt having to check OOM conditions.  Also, only
check __GFP_NOFAIL when the charge would actually fail.
Signed-off-by: NJohannes Weiner <hannes@cmpxchg.org>
Acked-by: NMichal Hocko <mhocko@suse.cz>
Cc: Hugh Dickins <hughd@google.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Vladimir Davydov <vdavydov@parallels.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

These patches rework memcg charge lifetime to integrate more naturally
with the lifetime of user pages.  This drastically simplifies the code
and reduces charging and uncharging overhead.  The most expensive part
of charging and uncharging is the page_cgroup bit spinlock, which is
removed entirely after this series.

Here are the top-10 profile entries of a stress test that reads a 128G
sparse file on a freshly booted box, without even a dedicated cgroup
(i.e. executing in the root memcg).  Before:

    15.36%              cat  [kernel.kallsyms]   [k] copy_user_generic_string
    13.31%              cat  [kernel.kallsyms]   [k] memset
    11.48%              cat  [kernel.kallsyms]   [k] do_mpage_readpage
     4.23%              cat  [kernel.kallsyms]   [k] get_page_from_freelist
     2.38%              cat  [kernel.kallsyms]   [k] put_page
     2.32%              cat  [kernel.kallsyms]   [k] __mem_cgroup_commit_charge
     2.18%          kswapd0  [kernel.kallsyms]   [k] __mem_cgroup_uncharge_common
     1.92%          kswapd0  [kernel.kallsyms]   [k] shrink_page_list
     1.86%              cat  [kernel.kallsyms]   [k] __radix_tree_lookup
     1.62%              cat  [kernel.kallsyms]   [k] __pagevec_lru_add_fn

After:

    15.67%           cat  [kernel.kallsyms]   [k] copy_user_generic_string
    13.48%           cat  [kernel.kallsyms]   [k] memset
    11.42%           cat  [kernel.kallsyms]   [k] do_mpage_readpage
     3.98%           cat  [kernel.kallsyms]   [k] get_page_from_freelist
     2.46%           cat  [kernel.kallsyms]   [k] put_page
     2.13%       kswapd0  [kernel.kallsyms]   [k] shrink_page_list
     1.88%           cat  [kernel.kallsyms]   [k] __radix_tree_lookup
     1.67%           cat  [kernel.kallsyms]   [k] __pagevec_lru_add_fn
     1.39%       kswapd0  [kernel.kallsyms]   [k] free_pcppages_bulk
     1.30%           cat  [kernel.kallsyms]   [k] kfree

As you can see, the memcg footprint has shrunk quite a bit.

   text    data     bss     dec     hex filename
  37970    9892     400   48262    bc86 mm/memcontrol.o.old
  35239    9892     400   45531    b1db mm/memcontrol.o

This patch (of 13):

This function was split out because mem_cgroup_try_charge() got too big.
But having essentially one sequence of operations arbitrarily split in
half is not good for reworking the code.  Fold it back in.
Signed-off-by: NJohannes Weiner <hannes@cmpxchg.org>
Acked-by: NMichal Hocko <mhocko@suse.cz>
Cc: Hugh Dickins <hughd@google.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Vladimir Davydov <vdavydov@parallels.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Paul Furtado has reported the following GPF:

  general protection fault: 0000 [#1] SMP
  Modules linked in: ipv6 dm_mod xen_netfront coretemp hwmon x86_pkg_temp_thermal crc32_pclmul crc32c_intel ghash_clmulni_intel aesni_intel ablk_helper cryptd lrw gf128mul glue_helper aes_x86_64 microcode pcspkr ext4 jbd2 mbcache raid0 xen_blkfront
  CPU: 3 PID: 3062 Comm: java Not tainted 3.16.0-rc5 #1
  task: ffff8801cfe8f170 ti: ffff8801d2ec4000 task.ti: ffff8801d2ec4000
  RIP: e030:mem_cgroup_oom_synchronize+0x140/0x240
  RSP: e02b:ffff8801d2ec7d48  EFLAGS: 00010283
  RAX: 0000000000000001 RBX: ffff88009d633800 RCX: 000000000000000e
  RDX: fffffffffffffffe RSI: ffff88009d630200 RDI: ffff88009d630200
  RBP: ffff8801d2ec7da8 R08: 0000000000000012 R09: 00000000fffffffe
  R10: 0000000000000000 R11: 0000000000000000 R12: ffff88009d633800
  R13: ffff8801d2ec7d48 R14: dead000000100100 R15: ffff88009d633a30
  FS:  00007f1748bb4700(0000) GS:ffff8801def80000(0000) knlGS:0000000000000000
  CS:  e033 DS: 0000 ES: 0000 CR0: 000000008005003b
  CR2: 00007f4110300308 CR3: 00000000c05f7000 CR4: 0000000000002660
  Call Trace:
    pagefault_out_of_memory+0x18/0x90
    mm_fault_error+0xa9/0x1a0
    __do_page_fault+0x478/0x4c0
    do_page_fault+0x2c/0x40
    page_fault+0x28/0x30
  Code: 44 00 00 48 89 df e8 40 ca ff ff 48 85 c0 49 89 c4 74 35 4c 8b b0 30 02 00 00 4c 8d b8 30 02 00 00 4d 39 fe 74 1b 0f 1f 44 00 00 <49> 8b 7e 10 be 01 00 00 00 e8 42 d2 04 00 4d 8b 36 4d 39 fe 75
  RIP  mem_cgroup_oom_synchronize+0x140/0x240

Commit fb2a6fc5 ("mm: memcg: rework and document OOM waiting and
wakeup") has moved mem_cgroup_oom_notify outside of memcg_oom_lock
assuming it is protected by the hierarchical OOM-lock.

Although this is true for the notification part the protection doesn't
cover unregistration of event which can happen in parallel now so
mem_cgroup_oom_notify can see already unlinked and/or freed
mem_cgroup_eventfd_list.

Fix this by using memcg_oom_lock also in mem_cgroup_oom_notify.

Addresses https://bugzilla.kernel.org/show_bug.cgi?id=80881

Fixes: fb2a6fc5 (mm: memcg: rework and document OOM waiting and wakeup)
Signed-off-by: NMichal Hocko <mhocko@suse.cz>
Reported-by: NPaul Furtado <paulfurtado91@gmail.com>
Tested-by: NPaul Furtado <paulfurtado91@gmail.com>
Acked-by: NJohannes Weiner <hannes@cmpxchg.org>
Cc: <stable@vger.kernel.org>	[3.12+]
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Until now, cftype arrays carried files for both the default and legacy
hierarchies and the files which needed to be used on only one of them
were flagged with either CFTYPE_ONLY_ON_DFL or CFTYPE_INSANE.  This
gets confusing very quickly and we may end up exposing interface files
to the default hierarchy without thinking it through.

This patch makes cgroup core provide separate sets of interfaces for
cftype handling so that the cftypes for the default and legacy
hierarchies are clearly distinguished.  The previous two patches
renamed the existing ones so that they clearly indicate that they're
for the legacy hierarchies.  This patch adds the interface for the
default hierarchy and apply them selectively depending on the
hierarchy type.

* cftypes added through cgroup_subsys->dfl_cftypes and
  cgroup_add_dfl_cftypes() only show up on the default hierarchy.

* cftypes added through cgroup_subsys->legacy_cftypes and
  cgroup_add_legacy_cftypes() only show up on the legacy hierarchies.

* cgroup_subsys->dfl_cftypes and ->legacy_cftypes can point to the
  same array for the cases where the interface files are identical on
  both types of hierarchies.

* This makes all the existing subsystem interface files legacy-only by
  default and all subsystems will have no interface file created when
  enabled on the default hierarchy.  Each subsystem should explicitly
  review and compose the interface for the default hierarchy.

* A boot param "cgroup__DEVEL__legacy_files_on_dfl" is added which
  makes subsystems which haven't decided the interface files for the
  default hierarchy to present the legacy files on the default
  hierarchy so that its behavior on the default hierarchy can be
  tested.  As the awkward name suggests, this is for development only.

* memcg's CFTYPE_INSANE on "use_hierarchy" is noop now as the whole
  array isn't used on the default hierarchy.  The flag is removed.

v2: Updated documentation for cgroup__DEVEL__legacy_files_on_dfl.

v3: Clear CFTYPE_ONLY_ON_DFL and CFTYPE_INSANE when cfts are removed
    as suggested by Li.
Signed-off-by: NTejun Heo <tj@kernel.org>
Acked-by: NNeil Horman <nhorman@tuxdriver.com>
Acked-by: NLi Zefan <lizefan@huawei.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Aristeu Rozanski <aris@redhat.com>
Cc: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>

Currently, cftypes added by cgroup_add_cftypes() are used for both the
unified default hierarchy and legacy ones and subsystems can mark each
file with either CFTYPE_ONLY_ON_DFL or CFTYPE_INSANE if it has to
appear only on one of them.  This is quite hairy and error-prone.
Also, we may end up exposing interface files to the default hierarchy
without thinking it through.

cgroup_subsys will grow two separate cftype addition functions and
apply each only on the hierarchies of the matching type.  This will
allow organizing cftypes in a lot clearer way and encourage subsystems
to scrutinize the interface which is being exposed in the new default
hierarchy.

In preparation, this patch adds cgroup_add_legacy_cftypes() which
currently is a simple wrapper around cgroup_add_cftypes() and replaces
all cgroup_add_cftypes() usages with it.

While at it, this patch drops a completely spurious return from
__hugetlb_cgroup_file_init().

This patch doesn't introduce any functional differences.
Signed-off-by: NTejun Heo <tj@kernel.org>
Acked-by: NNeil Horman <nhorman@tuxdriver.com>
Acked-by: NLi Zefan <lizefan@huawei.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>

Currently, cgroup_subsys->base_cftypes is used for both the unified
default hierarchy and legacy ones and subsystems can mark each file
with either CFTYPE_ONLY_ON_DFL or CFTYPE_INSANE if it has to appear
only on one of them.  This is quite hairy and error-prone.  Also, we
may end up exposing interface files to the default hierarchy without
thinking it through.

cgroup_subsys will grow two separate cftype arrays and apply each only
on the hierarchies of the matching type.  This will allow organizing
cftypes in a lot clearer way and encourage subsystems to scrutinize
the interface which is being exposed in the new default hierarchy.

In preparation, this patch renames cgroup_subsys->base_cftypes to
cgroup_subsys->legacy_cftypes.  This patch is pure rename.
Signed-off-by: NTejun Heo <tj@kernel.org>
Acked-by: NNeil Horman <nhorman@tuxdriver.com>
Acked-by: NLi Zefan <lizefan@huawei.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Aristeu Rozanski <aris@redhat.com>
Cc: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>

sane_behavior has been used as a development vehicle for the default
unified hierarchy.  Now that the default hierarchy is in place, the
flag became redundant and confusing as its usage is allowed on all
hierarchies.  There are gonna be either the default hierarchy or
legacy ones.  Let's make that clear by removing sane_behavior support
on non-default hierarchies.

This patch replaces cgroup_sane_behavior() with cgroup_on_dfl().  The
comment on top of CGRP_ROOT_SANE_BEHAVIOR is moved to on top of
cgroup_on_dfl() with sane_behavior specific part dropped.

On the default and legacy hierarchies w/o sane_behavior, this
shouldn't cause any behavior differences.
Signed-off-by: NTejun Heo <tj@kernel.org>
Acked-by: NVivek Goyal <vgoyal@redhat.com>
Acked-by: NLi Zefan <lizefan@huawei.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.cz>

Currently, the blkio subsystem attributes all of writeback IOs to the
root.  One of the issues is that there's no way to tell who originated
a writeback IO from block layer.  Those IOs are usually issued
asynchronously from a task which didn't have anything to do with
actually generating the dirty pages.  The memory subsystem, when
enabled, already keeps track of the ownership of each dirty page and
it's desirable for blkio to piggyback instead of adding its own
per-page tag.

cgroup now has a mechanism to express such dependency -
cgroup_subsys->depends_on.  This patch declares that blkcg depends on
memcg so that memcg is enabled automatically on the default hierarchy
when available.  Future changes will make blkcg map the memcg tag to
find out the cgroup to blame for writeback IOs.

As this means that a memcg may be made invisible, this patch also
implements css_reset() for memcg which resets its basic
configurations.  This implementation will probably need to be expanded
to cover other states which are used in the default hierarchy.

v2: blkcg's dependency on memcg is wrapped with CONFIG_MEMCG to avoid
    build failure.  Reported by kbuild test robot.
Signed-off-by: NTejun Heo <tj@kernel.org>
Acked-by: NLi Zefan <lizefan@huawei.com>
Acked-by: NJohannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: Jens Axboe <axboe@kernel.dk>

Signed-off-by: NJohannes Weiner <hannes@cmpxchg.org>
Acked-by: NMichal Hocko <mhocko@suse.cz>
Cc: Jianyu Zhan <nasa4836@gmail.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Memcg zoneinfo lookup sites have either the page, the zone, or the node
id and zone index, but sites that only have the zone have to look up the
node id and zone index themselves, whereas sites that already have those
two integers use a function for a simple pointer chase.

Provide mem_cgroup_zone_zoneinfo() that takes a zone pointer and let
sites that already have node id and zone index - all for each node, for
each zone iterators - use &memcg->nodeinfo[nid]->zoneinfo[zid].

Rename page_cgroup_zoneinfo() to mem_cgroup_page_zoneinfo() to match.
Signed-off-by: NJianyu Zhan <nasa4836@gmail.com>
Signed-off-by: NJohannes Weiner <hannes@cmpxchg.org>
Acked-by: NMichal Hocko <mhocko@suse.cz>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Memory reclaim always uses swappiness of the reclaim target memcg
(origin of the memory pressure) or vm_swappiness for global memory
reclaim.  This behavior was consistent (except for difference between
global and hard limit reclaim) because swappiness was enforced to be
consistent within each memcg hierarchy.

After "mm: memcontrol: remove hierarchy restrictions for swappiness and
oom_control" each memcg can have its own swappiness independent of
hierarchical parents, though, so the consistency guarantee is gone.
This can lead to an unexpected behavior.  Say that a group is explicitly
configured to not swapout by memory.swappiness=0 but its memory gets
swapped out anyway when the memory pressure comes from its parent with a
It is also unexpected that the knob is meaningless without setting the
hard limit which would trigger the reclaim and enforce the swappiness.
There are setups where the hard limit is configured higher in the
hierarchy by an administrator and children groups are under control of
somebody else who is interested in the swapout behavior but not
necessarily about the memory limit.

From a semantic point of view swappiness is an attribute defining anon
vs.
 file proportional scanning of LRU which is memcg specific (unlike
charges which are propagated up the hierarchy) so it should be applied
to the particular memcg's LRU regardless where the memory pressure comes
from.

This patch removes vmscan_swappiness() and stores the swappiness into
the scan_control structure.  mem_cgroup_swappiness is then used to
provide the correct value before shrink_lruvec is called.  The global
vm_swappiness is used for the root memcg.

[hughd@google.com: oopses immediately when booted with cgroup_disable=memory]
Signed-off-by: NMichal Hocko <mhocko@suse.cz>
Acked-by: NJohannes Weiner <hannes@cmpxchg.org>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: NHugh Dickins <hughd@google.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

mem_cgroup_force_empty_list() can iterate a large number of pages on an
lru and mem_cgroup_move_parent() doesn't return an errno unless certain
criteria, none of which indicate that the iteration may be taking too
long, is met.

We have encountered the following stack trace many times indicating
"need_resched set for > 51000020 ns (51 ticks) without schedule", for
example:

	scheduler_tick()
	<timer irq>
	mem_cgroup_move_account+0x4d/0x1d5
	mem_cgroup_move_parent+0x8d/0x109
	mem_cgroup_reparent_charges+0x149/0x2ba
	mem_cgroup_css_offline+0xeb/0x11b
	cgroup_offline_fn+0x68/0x16b
	process_one_work+0x129/0x350

If this iteration is taking too long, we still need to do cond_resched()
even when an individual page is not busy.

[rientjes@google.com: changelog]
Signed-off-by: NHugh Dickins <hughd@google.com>
Signed-off-by: NDavid Rientjes <rientjes@google.com>
Acked-by: NJohannes Weiner <hannes@cmpxchg.org>
Acked-by: NMichal Hocko <mhocko@suse.cz>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Current names are rather inconsistent. Let's try to improve them.

Brief change log:

** old name **                          ** new name **

kmem_cache_create_memcg                 memcg_create_kmem_cache
memcg_kmem_create_cache                 memcg_regsiter_cache
memcg_kmem_destroy_cache                memcg_unregister_cache

kmem_cache_destroy_memcg_children       memcg_cleanup_cache_params
mem_cgroup_destroy_all_caches           memcg_unregister_all_caches

create_work                             memcg_register_cache_work
memcg_create_cache_work_func            memcg_register_cache_func
memcg_create_cache_enqueue              memcg_schedule_register_cache
Signed-off-by: NVladimir Davydov <vdavydov@parallels.com>
Acked-by: NMichal Hocko <mhocko@suse.cz>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

It isn't worth complicating the code by allocating it on the first access,
because it only takes 256 bytes.
Signed-off-by: NVladimir Davydov <vdavydov@parallels.com>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Instead of calling back to memcontrol.c from kmem_cache_create_memcg in
order to just create the name of a per memcg cache, let's allocate it in
place.  We only need to pass the memcg name to kmem_cache_create_memcg for
that - everything else can be done in slab_common.c.
Signed-off-by: NVladimir Davydov <vdavydov@parallels.com>
Acked-by: NMichal Hocko <mhocko@suse.cz>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Signed-off-by: NQiang Huang <h.huangqiang@huawei.com>
Acked-by: NMichal Hocko <mhocko@suse.cz>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

It is only used in __mem_cgroup_begin_update_page_stat(), the name is
confusing and 2 routines for one thing also confuse people, so fold this
function seems more clear.

[akpm@linux-foundation.org: fix typo, per Michal]
Signed-off-by: NQiang Huang <h.huangqiang@huawei.com>
Acked-by: NMichal Hocko <mhocko@suse.cz>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

static values are automatically initialized to NULL
Signed-off-by: NFabian Frederick <fabf@skynet.be>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Replace places where __get_cpu_var() is used for an address calculation
with this_cpu_ptr().
Signed-off-by: NChristoph Lameter <cl@linux.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

At present, we have the following mutexes protecting data related to per
memcg kmem caches:

 - slab_mutex.  This one is held during the whole kmem cache creation
   and destruction paths.  We also take it when updating per root cache
   memcg_caches arrays (see memcg_update_all_caches).  As a result, taking
   it guarantees there will be no changes to any kmem cache (including per
   memcg).  Why do we need something else then?  The point is it is
   private to slab implementation and has some internal dependencies with
   other mutexes (get_online_cpus).  So we just don't want to rely upon it
   and prefer to introduce additional mutexes instead.

 - activate_kmem_mutex.  Initially it was added to synchronize
   initializing kmem limit (memcg_activate_kmem).  However, since we can
   grow per root cache memcg_caches arrays only on kmem limit
   initialization (see memcg_update_all_caches), we also employ it to
   protect against memcg_caches arrays relocation (e.g.  see
   __kmem_cache_destroy_memcg_children).

 - We have a convention not to take slab_mutex in memcontrol.c, but we
   want to walk over per memcg memcg_slab_caches lists there (e.g.  for
   destroying all memcg caches on offline).  So we have per memcg
   slab_caches_mutex's protecting those lists.

The mutexes are taken in the following order:

   activate_kmem_mutex -> slab_mutex -> memcg::slab_caches_mutex

Such a syncrhonization scheme has a number of flaws, for instance:

 - We can't call kmem_cache_{destroy,shrink} while walking over a
   memcg::memcg_slab_caches list due to locking order.  As a result, in
   mem_cgroup_destroy_all_caches we schedule the
   memcg_cache_params::destroy work shrinking and destroying the cache.

 - We don't have a mutex to synchronize per memcg caches destruction
   between memcg offline (mem_cgroup_destroy_all_caches) and root cache
   destruction (__kmem_cache_destroy_memcg_children).  Currently we just
   don't bother about it.

This patch simplifies it by substituting per memcg slab_caches_mutex's
with the global memcg_slab_mutex.  It will be held whenever a new per
memcg cache is created or destroyed, so it protects per root cache
memcg_caches arrays and per memcg memcg_slab_caches lists.  The locking
order is following:

   activate_kmem_mutex -> memcg_slab_mutex -> slab_mutex

This allows us to call kmem_cache_{create,shrink,destroy} under the
memcg_slab_mutex.  As a result, we don't need memcg_cache_params::destroy
work any more - we can simply destroy caches while iterating over a per
memcg slab caches list.

Also using the global mutex simplifies synchronization between concurrent
per memcg caches creation/destruction, e.g.  mem_cgroup_destroy_all_caches
vs __kmem_cache_destroy_memcg_children.

The downside of this is that we substitute per-memcg slab_caches_mutex's
with a hummer-like global mutex, but since we already take either the
slab_mutex or the cgroup_mutex along with a memcg::slab_caches_mutex, it
shouldn't hurt concurrency a lot.
Signed-off-by: NVladimir Davydov <vdavydov@parallels.com>
Acked-by: NJohannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Glauber Costa <glommer@gmail.com>
Cc: Pekka Enberg <penberg@kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Currently we have two pairs of kmemcg-related functions that are called on
slab alloc/free.  The first is memcg_{bind,release}_pages that count the
total number of pages allocated on a kmem cache.  The second is
memcg_{un}charge_slab that {un}charge slab pages to kmemcg resource
counter.  Let's just merge them to keep the code clean.
Signed-off-by: NVladimir Davydov <vdavydov@parallels.com>
Acked-by: NJohannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Glauber Costa <glommer@gmail.com>
Cc: Pekka Enberg <penberg@kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

This patchset is a part of preparations for kmemcg re-parenting.  It
targets at simplifying kmemcg work-flows and synchronization.

First, it removes async per memcg cache destruction (see patches 1, 2).
Now caches are only destroyed on memcg offline.  That means the caches
that are not empty on memcg offline will be leaked.  However, they are
already leaked, because memcg_cache_params::nr_pages normally never drops
to 0 so the destruction work is never scheduled except kmem_cache_shrink
is called explicitly.  In the future I'm planning reaping such dead caches
on vmpressure or periodically.

Second, it substitutes per memcg slab_caches_mutex's with the global
memcg_slab_mutex, which should be taken during the whole per memcg cache
creation/destruction path before the slab_mutex (see patch 3).  This
greatly simplifies synchronization among various per memcg cache
creation/destruction paths.

I'm still not quite sure about the end picture, in particular I don't know
whether we should reap dead memcgs' kmem caches periodically or try to
merge them with their parents (see https://lkml.org/lkml/2014/4/20/38 for
more details), but whichever way we choose, this set looks like a
reasonable change to me, because it greatly simplifies kmemcg work-flows
and eases further development.

This patch (of 3):

After a memcg is offlined, we mark its kmem caches that cannot be deleted
right now due to pending objects as dead by setting the
memcg_cache_params::dead flag, so that memcg_release_pages will schedule
cache destruction (memcg_cache_params::destroy) as soon as the last slab
of the cache is freed (memcg_cache_params::nr_pages drops to zero).

I guess the idea was to destroy the caches as soon as possible, i.e.
immediately after freeing the last object.  However, it just doesn't work
that way, because kmem caches always preserve some pages for the sake of
performance, so that nr_pages never gets to zero unless the cache is
shrunk explicitly using kmem_cache_shrink.  Of course, we could account
the total number of objects on the cache or check if all the slabs
allocated for the cache are empty on kmem_cache_free and schedule
destruction if so, but that would be too costly.

Thus we have a piece of code that works only when we explicitly call
kmem_cache_shrink, but complicates the whole picture a lot.  Moreover,
it's racy in fact.  For instance, kmem_cache_shrink may free the last slab
and thus schedule cache destruction before it finishes checking that the
cache is empty, which can lead to use-after-free.

So I propose to remove this async cache destruction from
memcg_release_pages, and check if the cache is empty explicitly after
calling kmem_cache_shrink instead.  This will simplify things a lot w/o
introducing any functional changes.

And regarding dead memcg caches (i.e.  those that are left hanging around
after memcg offline for they have objects), I suppose we should reap them
either periodically or on vmpressure as Glauber suggested initially.  I'm
going to implement this later.
Signed-off-by: NVladimir Davydov <vdavydov@parallels.com>
Acked-by: NJohannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Glauber Costa <glommer@gmail.com>
Cc: Pekka Enberg <penberg@kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Eric has reported that he can see task(s) stuck in memcg OOM handler
regularly.  The only way out is to

	echo 0 > $GROUP/memory.oom_control

His usecase is:

- Setup a hierarchy with memory and the freezer (disable kernel oom and
  have a process watch for oom).

- In that memory cgroup add a process with one thread per cpu.

- In one thread slowly allocate once per second I think it is 16M of ram
  and mlock and dirty it (just to force the pages into ram and stay
  there).

- When oom is achieved loop:
  * attempt to freeze all of the tasks.
  * if frozen send every task SIGKILL, unfreeze, remove the directory in
    cgroupfs.

Eric has then pinpointed the issue to be memcg specific.

All tasks are sitting on the memcg_oom_waitq when memcg oom is disabled.
Those that have received fatal signal will bypass the charge and should
continue on their way out.  The tricky part is that the exit path might
trigger a page fault (e.g.  exit_robust_list), thus the memcg charge,
while its memcg is still under OOM because nobody has released any charges
yet.

Unlike with the in-kernel OOM handler the exiting task doesn't get
TIF_MEMDIE set so it doesn't shortcut further charges of the killed task
and falls to the memcg OOM again without any way out of it as there are no
fatal signals pending anymore.

This patch fixes the issue by checking PF_EXITING early in
mem_cgroup_try_charge and bypass the charge same as if it had fatal
signal pending or TIF_MEMDIE set.

Normally exiting tasks (aka not killed) will bypass the charge now but
this should be OK as the task is leaving and will release memory and
increasing the memory pressure just to release it in a moment seems
dubious wasting of cycles.  Besides that charges after exit_signals should
be rare.

I am bringing this patch again (rebased on the current mmotm tree). I
hope we can move forward finally. If there is still an opposition then
I would really appreciate a concurrent approach so that we can discuss
alternatives.

http://comments.gmane.org/gmane.linux.kernel.stable/77650 is a reference
to the followup discussion when the patch has been dropped from the mmotm
last time.
Reported-by: NEric W. Biederman <ebiederm@xmission.com>
Signed-off-by: NMichal Hocko <mhocko@suse.cz>
Acked-by: NDavid Rientjes <rientjes@google.com>
Acked-by: NJohannes Weiner <hannes@cmpxchg.org>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

It is only used in slab and should not be used anywhere else so there is
no need in exporting it.
Signed-off-by: NVladimir Davydov <vdavydov@parallels.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Per-memcg swappiness and oom killing can currently not be tweaked on a
memcg that is part of a hierarchy, but not the root of that hierarchy.
Users have complained that they can't configure this when they turned on
hierarchy mode.  In fact, with hierarchy mode becoming the default, this
restriction disables the tunables entirely.

But there is no good reason for this restriction.  The settings for
swappiness and OOM killing are taken from whatever memcg whose limit
triggered reclaim and OOM invocation, regardless of its position in the
hierarchy tree.

Allow setting swappiness on any group.  The knob on the root memcg
already reads the global VM swappiness, make it writable as well.

Allow disabling the OOM killer on any non-root memcg.
Signed-off-by: NJohannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Tejun Heo <tj@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Currently to allocate a page that should be charged to kmemcg (e.g.
threadinfo), we pass __GFP_KMEMCG flag to the page allocator.  The page
allocated is then to be freed by free_memcg_kmem_pages.  Apart from
looking asymmetrical, this also requires intrusion to the general
allocation path.  So let's introduce separate functions that will
alloc/free pages charged to kmemcg.

The new functions are called alloc_kmem_pages and free_kmem_pages.  They
should be used when the caller actually would like to use kmalloc, but
has to fall back to the page allocator for the allocation is large.
They only differ from alloc_pages and free_pages in that besides
allocating or freeing pages they also charge them to the kmem resource
counter of the current memory cgroup.

[sfr@canb.auug.org.au: export kmalloc_order() to modules]
Signed-off-by: NVladimir Davydov <vdavydov@parallels.com>
Acked-by: NGreg Thelen <gthelen@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: NMichal Hocko <mhocko@suse.cz>
Cc: Glauber Costa <glommer@gmail.com>
Cc: Christoph Lameter <cl@linux-foundation.org>
Cc: Pekka Enberg <penberg@kernel.org>
Signed-off-by: NStephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

We have only a few places where we actually want to charge kmem so
instead of intruding into the general page allocation path with
__GFP_KMEMCG it's better to explictly charge kmem there.  All kmem
charges will be easier to follow that way.

This is a step towards removing __GFP_KMEMCG.  It removes __GFP_KMEMCG
from memcg caches' allocflags.  Instead it makes slab allocation path
call memcg_charge_kmem directly getting memcg to charge from the cache's
memcg params.

This also eliminates any possibility of misaccounting an allocation
going from one memcg's cache to another memcg, because now we always
charge slabs against the memcg the cache belongs to.  That's why this
patch removes the big comment to memcg_kmem_get_cache.
Signed-off-by: NVladimir Davydov <vdavydov@parallels.com>
Acked-by: NGreg Thelen <gthelen@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: NMichal Hocko <mhocko@suse.cz>
Cc: Glauber Costa <glommer@gmail.com>
Cc: Christoph Lameter <cl@linux-foundation.org>
Cc: Pekka Enberg <penberg@kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Commit 284f39af ("mm: memcg: push !mm handling out to page cache
charge function") explicitly checks for page cache charges without any
mm context (from kernel thread context[1]).

This seemed to be the only possible case where memory could be charged
without mm context so commit 03583f1a ("memcg: remove unnecessary
!mm check from try_get_mem_cgroup_from_mm()") removed the mm check from
get_mem_cgroup_from_mm().  This however caused another NULL ptr
dereference during early boot when loopback kernel thread splices to
tmpfs as reported by Stephan Kulow:

  BUG: unable to handle kernel NULL pointer dereference at 0000000000000360
  IP: get_mem_cgroup_from_mm.isra.42+0x2b/0x60
  Oops: 0000 [#1] SMP
  Modules linked in: btrfs dm_multipath dm_mod scsi_dh multipath raid10 raid456 async_raid6_recov async_memcpy async_pq raid6_pq async_xor xor async_tx raid1 raid0 md_mod parport_pc parport nls_utf8 isofs usb_storage iscsi_ibft iscsi_boot_sysfs arc4 ecb fan thermal nfs lockd fscache nls_iso8859_1 nls_cp437 sg st hid_generic usbhid af_packet sunrpc sr_mod cdrom ata_generic uhci_hcd virtio_net virtio_blk ehci_hcd usbcore ata_piix floppy processor button usb_common virtio_pci virtio_ring virtio edd squashfs loop ppa]
  CPU: 0 PID: 97 Comm: loop1 Not tainted 3.15.0-rc5-5-default #1
  Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
  Call Trace:
    __mem_cgroup_try_charge_swapin+0x40/0xe0
    mem_cgroup_charge_file+0x8b/0xd0
    shmem_getpage_gfp+0x66b/0x7b0
    shmem_file_splice_read+0x18f/0x430
    splice_direct_to_actor+0xa2/0x1c0
    do_lo_receive+0x5a/0x60 [loop]
    loop_thread+0x298/0x720 [loop]
    kthread+0xc6/0xe0
    ret_from_fork+0x7c/0xb0

Also Branimir Maksimovic reported the following oops which is tiggered
for the swapcache charge path from the accounting code for kernel threads:

  CPU: 1 PID: 160 Comm: kworker/u8:5 Tainted: P           OE 3.15.0-rc5-core2-custom #159
  Hardware name: System manufacturer System Product Name/MAXIMUSV GENE, BIOS 1903 08/19/2013
  task: ffff880404e349b0 ti: ffff88040486a000 task.ti: ffff88040486a000
  RIP: get_mem_cgroup_from_mm.isra.42+0x2b/0x60
  Call Trace:
    __mem_cgroup_try_charge_swapin+0x45/0xf0
    mem_cgroup_charge_file+0x9c/0xe0
    shmem_getpage_gfp+0x62c/0x770
    shmem_write_begin+0x38/0x40
    generic_perform_write+0xc5/0x1c0
    __generic_file_aio_write+0x1d1/0x3f0
    generic_file_aio_write+0x4f/0xc0
    do_sync_write+0x5a/0x90
    do_acct_process+0x4b1/0x550
    acct_process+0x6d/0xa0
    do_exit+0x827/0xa70
    kthread+0xc3/0xf0

This patch fixes the issue by reintroducing mm check into
get_mem_cgroup_from_mm.  We could do the same trick in
__mem_cgroup_try_charge_swapin as we do for the regular page cache path
but it is not worth troubles.  The check is not that expensive and it is
better to have get_mem_cgroup_from_mm more robust.

[1] - http://marc.info/?l=linux-mm&m=139463617808941&w=2

Fixes: 03583f1a ("memcg: remove unnecessary !mm check from try_get_mem_cgroup_from_mm()")
Reported-and-tested-by: NStephan Kulow <coolo@suse.com>
Reported-by: NBranimir Maksimovic <branimir.maksimovic@gmail.com>
Signed-off-by: NMichal Hocko <mhocko@suse.cz>
Acked-by: NJohannes Weiner <hannes@cmpxchg.org>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Currently, memcg_has_children() and mem_cgroup_hierarchy_write()
directly test cgroup->children for list emptiness.  It's semantically
correct in traditional hierarchies as it actually wants to test for
any children dead or alive; however, cgroup->children is not a
published field and scheduled to go away.

This patch moves out .use_hierarchy test out of memcg_has_children()
and updates it to use css_next_child() to test whether there exists
any children.  With .use_hierarchy test moved out, it can also be used
by mem_cgroup_hierarchy_write().

A side note: As .use_hierarchy is going away, it doesn't really matter
but I'm not sure about how it's used in __memcg_activate_kmem().  The
condition tested by memcg_has_children() is mushy when seen from
userland as its result is affected by dead csses which aren't visible
from userland.  I think the rule would be a lot clearer if we have a
dedicated "freshly minted" flag which gets cleared when the first task
is migrated into it or the first child is created and then gate
activation with that.

v2: Added comment noting that testing use_hierarchy is the
    responsibility of the callers of memcg_has_children() as suggested
    by Michal Hocko.
Signed-off-by: NTejun Heo <tj@kernel.org>
Acked-by: NMichal Hocko <mhocko@suse.cz>
Acked-by: NLi Zefan <lizefan@huawei.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>

Tejun has correctly pointed out that tasks/children test in
mem_cgroup_force_empty is not correct because there is no other locking
which preserves this state throughout the rest of the function so both
new tasks can join the group or new children groups can be added while
somebody is writing to memory.force_empty. A new task would break
mem_cgroup_reparent_charges expectation that all failures as described
by mem_cgroup_force_empty_list are temporal and there is no way out.

The main use case for the knob as described by
Documentation/cgroups/memory.txt is to:
"
  The typical use case for this interface is before calling rmdir().
  Because rmdir() moves all pages to parent, some out-of-use page caches can be
  moved to the parent. If you want to avoid that, force_empty will be useful.
"

This means that reparenting is not really required as rmdir will
reparent pages implicitly from the safe context. If we remove it from
mem_cgroup_force_empty then we are safe even with existing tasks because
the number of reclaim attempts is bounded. Moreover the knob still does
what the documentation claims (modulo reparenting which doesn't make any
difference) and users might expect. Longterm we want to deprecate the
whole knob and put the reparented pages to the tail of parent LRU during
cgroup removal.

tj: Removed unused variable @cgrp from mem_cgroup_force_empty()
Signed-off-by: NMichal Hocko <mhocko@suse.cz>
Acked-by: NJohannes Weiner <hannes@cmpxchg.org>
Acked-by: NLi Zefan <lizefan@huawei.com>
Signed-off-by: NTejun Heo <tj@kernel.org>

cgroup in general is moving towards using cgroup_subsys_state as the
fundamental structural component and css_parent() was introduced to
convert from using cgroup->parent to css->parent.  It was quite some
time ago and we're moving forward with making css more prominent.

This patch drops the trivial wrapper css_parent() and let the users
dereference css->parent.  While at it, explicitly mark fields of css
which are public and immutable.

v2: New usage from device_cgroup.c converted.
Signed-off-by: NTejun Heo <tj@kernel.org>
Acked-by: NMichal Hocko <mhocko@suse.cz>
Acked-by: NNeil Horman <nhorman@tuxdriver.com>
Acked-by: N"David S. Miller" <davem@davemloft.net>
Acked-by: NLi Zefan <lizefan@huawei.com>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Johannes Weiner <hannes@cmpxchg.org>

cftype->trigger() is pointless.  It's trivial to ignore the input
buffer from a regular ->write() operation.  Convert all ->trigger()
users to ->write() and remove ->trigger().

This patch doesn't introduce any visible behavior changes.
Signed-off-by: NTejun Heo <tj@kernel.org>
Acked-by: NLi Zefan <lizefan@huawei.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.cz>

Convert all cftype->write_string() users to the new cftype->write()
which maps directly to kernfs write operation and has full access to
kernfs and cgroup contexts.  The conversions are mostly mechanical.

* @css and @cft are accessed using of_css() and of_cft() accessors
  respectively instead of being specified as arguments.

* Should return @nbytes on success instead of 0.

* @buf is not trimmed automatically.  Trim if necessary.  Note that
  blkcg and netprio don't need this as the parsers already handle
  whitespaces.

cftype->write_string() has no user left after the conversions and
removed.

While at it, remove unnecessary local variable @p in
cgroup_subtree_control_write() and stale comment about
CGROUP_LOCAL_BUFFER_SIZE in cgroup_freezer.c.

This patch doesn't introduce any visible behavior changes.

v2: netprio was missing from conversion.  Converted.
Signed-off-by: NTejun Heo <tj@kernel.org>
Acked-by: NAristeu Rozanski <arozansk@redhat.com>
Acked-by: NVivek Goyal <vgoyal@redhat.com>
Acked-by: NLi Zefan <lizefan@huawei.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Neil Horman <nhorman@tuxdriver.com>
Cc: "David S. Miller" <davem@davemloft.net>

Unlike the more usual refcnting, what css_tryget() provides is the
distinction between online and offline csses instead of protection
against upping a refcnt which already reached zero.  cgroup is
planning to provide actual tryget which fails if the refcnt already
reached zero.  Let's rename the existing trygets so that they clearly
indicate that they're onliness.

I thought about keeping the existing names as-are and introducing new
names for the planned actual tryget; however, given that each
controller participates in the synchronization of the online state, it
seems worthwhile to make it explicit that these functions are about
on/offline state.

Rename css_tryget() to css_tryget_online() and css_tryget_from_dir()
to css_tryget_online_from_dir().  This is pure rename.

v2: cgroup_freezer grew new usages of css_tryget().  Update
    accordingly.
Signed-off-by: NTejun Heo <tj@kernel.org>
Acked-by: NJohannes Weiner <hannes@cmpxchg.org>
Acked-by: NMichal Hocko <mhocko@suse.cz>
Acked-by: NLi Zefan <lizefan@huawei.com>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>

Dave Jones reports the following crash when find_get_pages_tag() runs
into an exceptional entry:

  kernel BUG at mm/filemap.c:1347!
  RIP: find_get_pages_tag+0x1cb/0x220
  Call Trace:
    find_get_pages_tag+0x36/0x220
    pagevec_lookup_tag+0x21/0x30
    filemap_fdatawait_range+0xbe/0x1e0
    filemap_fdatawait+0x27/0x30
    sync_inodes_sb+0x204/0x2a0
    sync_inodes_one_sb+0x19/0x20
    iterate_supers+0xb2/0x110
    sys_sync+0x44/0xb0
    ia32_do_call+0x13/0x13

  1343                         /*
  1344                          * This function is never used on a shmem/tmpfs
  1345                          * mapping, so a swap entry won't be found here.
  1346                          */
  1347                         BUG();

After commit 0cd6144a ("mm + fs: prepare for non-page entries in
page cache radix trees") this comment and BUG() are out of date because
exceptional entries can now appear in all mappings - as shadows of
recently evicted pages.

However, as Hugh Dickins notes,

  "it is truly surprising for a PAGECACHE_TAG_WRITEBACK (and probably
   any other PAGECACHE_TAG_*) to appear on an exceptional entry.

   I expect it comes down to an occasional race in RCU lookup of the
   radix_tree: lacking absolute synchronization, we might sometimes
   catch an exceptional entry, with the tag which really belongs with
   the unexceptional entry which was there an instant before."

And indeed, not only is the tree walk lockless, the tags are also read
in chunks, one radix tree node at a time.  There is plenty of time for
page reclaim to swoop in and replace a page that was already looked up
as tagged with a shadow entry.

Remove the BUG() and update the comment.  While reviewing all other
lookup sites for whether they properly deal with shadow entries of
evicted pages, update all the comments and fix memcg file charge moving
to not miss shmem/tmpfs swapcache pages.

Fixes: 0cd6144a ("mm + fs: prepare for non-page entries in page cache radix trees")
Signed-off-by: NJohannes Weiner <hannes@cmpxchg.org>
Reported-by: NDave Jones <davej@redhat.com>
Acked-by: NHugh Dickins <hughd@google.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Until now, cgroup->id has been used to identify all the associated
csses and css_from_id() takes cgroup ID and returns the matching css
by looking up the cgroup and then dereferencing the css associated
with it; however, now that the lifetimes of cgroup and css are
separate, this is incorrect and breaks on the unified hierarchy when a
controller is disabled and enabled back again before the previous
instance is released.

This patch adds css->id which is a subsystem-unique ID and converts
css_from_id() to look up by the new css->id instead.  memcg is the
only user of css_from_id() and also converted to use css->id instead.

For traditional hierarchies, this shouldn't make any functional
difference.
Signed-off-by: NTejun Heo <tj@kernel.org>
Acked-by: NMichal Hocko <mhocko@suse.cz>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Jianyu Zhan <nasa4836@gmail.com>
Acked-by: NLi Zefan <lizefan@huawei.com>