is_vma_resv_set(vma, HPAGE_RESV_OWNER) implys that this mapping is for
private.  So we don't need to check whether this mapping is for shared or
not.

This patch is just for clean-up.
Signed-off-by: NJoonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Aneesh Kumar <aneesh.kumar@linux.vnet.ibm.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Reviewed-by: NDavidlohr Bueso <davidlohr@hp.com>
Cc: David Gibson <david@gibson.dropbear.id.au>
Cc: Wanpeng Li <liwanp@linux.vnet.ibm.com>
Cc: Hillf Danton <dhillf@gmail.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

If we alloc hugepage with avoid_reserve, we don't dequeue reserved one.
So, we should check subpool counter when avoid_reserve.  This patch
implement it.
Signed-off-by: NJoonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Aneesh Kumar <aneesh.kumar@linux.vnet.ibm.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Davidlohr Bueso <davidlohr@hp.com>
Cc: David Gibson <david@gibson.dropbear.id.au>
Cc: Wanpeng Li <liwanp@linux.vnet.ibm.com>
Cc: Hillf Danton <dhillf@gmail.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

'reservations' is so long name as a variable and we use 'resv_map' to
represent 'struct resv_map' in other place.  To reduce confusion and
unreadability, change it.
Signed-off-by: NJoonsoo Kim <iamjoonsoo.kim@lge.com>
Reviewed-by: NAneesh Kumar <aneesh.kumar@linux.vnet.ibm.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Reviewed-by: NDavidlohr Bueso <davidlohr@hp.com>
Cc: David Gibson <david@gibson.dropbear.id.au>
Cc: Wanpeng Li <liwanp@linux.vnet.ibm.com>
Cc: Hillf Danton <dhillf@gmail.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Don't use the reserve pool when soft offlining a hugepage.  Check we have
free pages outside the reserve pool before we dequeue the huge page.
Otherwise, we can steal other's reserve page.
Signed-off-by: NJoonsoo Kim <iamjoonsoo.kim@lge.com>
Reviewed-by: NAneesh Kumar <aneesh.kumar@linux.vnet.ibm.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Reviewed-by: NDavidlohr Bueso <davidlohr@hp.com>
Cc: David Gibson <david@gibson.dropbear.id.au>
Cc: Wanpeng Li <liwanp@linux.vnet.ibm.com>
Cc: Hillf Danton <dhillf@gmail.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

lock_device_hotplug() serializes hotplug & online/offline operations.  The
lock is held in common sysfs online/offline interfaces and ACPI hotplug
code paths.

And here are the code paths:

- CPU & Mem online/offline via sysfs online
	store_online()->lock_device_hotplug()

- Mem online via sysfs state:
	store_mem_state()->lock_device_hotplug()

- ACPI CPU & Mem hot-add:
	acpi_scan_bus_device_check()->lock_device_hotplug()

- ACPI CPU & Mem hot-delete:
	acpi_scan_hot_remove()->lock_device_hotplug()

try_offline_node() off-lines a node if all memory sections and cpus are
removed on the node.  It is called from acpi_processor_remove() and
acpi_memory_remove_memory()->remove_memory() paths, both of which are in
the ACPI hotplug code.

try_offline_node() calls stop_machine() to stop all cpus while checking
all cpu status with the assumption that the caller is not protected from
CPU hotplug or CPU online/offline operations.  However, the caller is
always serialized with lock_device_hotplug().  Also, the code needs to be
properly serialized with a lock, not by stopping all cpus at a random
place with stop_machine().

This patch removes the use of stop_machine() in try_offline_node() and
adds comments to try_offline_node() and remove_memory() that
lock_device_hotplug() is required.
Signed-off-by: NToshi Kani <toshi.kani@hp.com>
Acked-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Tang Chen <tangchen@cn.fujitsu.com>
Cc: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
Cc: Wanpeng Li <liwanp@linux.vnet.ibm.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

add_memory() and remove_memory() can only handle a memory range aligned
with section.  There are problems when an unaligned range is added and
then deleted as follows:

 - add_memory() with an unaligned range succeeds, but __add_pages()
   called from add_memory() adds a whole section of pages even though
   a given memory range is less than the section size.
 - remove_memory() to the added unaligned range hits BUG_ON() in
   __remove_pages().

This patch changes add_memory() and remove_memory() to check if a given
memory range is aligned with section at the beginning.  As the result,
add_memory() fails with -EINVAL when a given range is unaligned, and does
not add such memory range.  This prevents remove_memory() to be called
with an unaligned range as well.  Note that remove_memory() has to use
BUG_ON() since this function cannot fail.

[akpm@linux-foundation.org: avoid printk warnings]
Signed-off-by: NToshi Kani <toshi.kani@hp.com>
Acked-by: NKOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Reviewed-by: NTang Chen <tangchen@cn.fujitsu.com>
Reviewed-by: NWanpeng Li <liwanp@linux.vnet.ibm.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Explicitly mention/recommend using the libhugetlbfs test cases when
changing related kernel code.  Developers that are unaware of the project
can easily miss this and introduce potential regressions that may or may
not be caught by community review.

Also do some cleanups that make the document visually easier to view at a
first glance.
Signed-off-by: NDavidlohr Bueso <davidlohr@hp.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

This helps performance on moderately dense random reads on SSD.

Transaction-Per-Second numbers provided by Taobao:

		QPS	case
		-------------------------------------------------------
		7536	disable context readahead totally
w/ patch:	7129	slower size rampup and start RA on the 3rd read
		6717	slower size rampup
w/o patch:	5581	unmodified context readahead

Before, readahead will be started whenever reading page N+1 when it happen
to read N recently.  After patch, we'll only start readahead when *three*
random reads happen to access pages N, N+1, N+2.  The probability of this
happening is extremely low for pure random reads, unless they are very
dense, which actually deserves some readahead.

Also start with a smaller readahead window.  The impact to interleaved
sequential reads should be small, because for a long run stream, the the
small readahead window rampup phase is negletable.

The context readahead actually benefits clustered random reads on HDD
whose seek cost is pretty high.  However as SSD is increasingly used for
random read workloads it's better for the context readahead to concentrate
on interleaved sequential reads.

Another SSD rand read test from Miao

        # file size:        2GB
        # read IO amount: 625MB
        sysbench --test=fileio          \
                --max-requests=10000    \
                --num-threads=1         \
                --file-num=1            \
                --file-block-size=64K   \
                --file-test-mode=rndrd  \
                --file-fsync-freq=0     \
                --file-fsync-end=off    run

shows the performance of btrfs grows up from 69MB/s to 121MB/s, ext4 from
104MB/s to 121MB/s.
Signed-off-by: NWu Fengguang <fengguang.wu@intel.com>
Tested-by: NTao Ma <tm@tao.ma>
Tested-by: NMiao Xie <miaox@cn.fujitsu.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Use "zone_is_initialized()" instead of "if (zone->wait_table)".
Simplify the code, no functional change.
Signed-off-by: NXishi Qiu <qiuxishi@huawei.com>
Cc: Cody P Schafer <cody@linux.vnet.ibm.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Use "zone_is_empty()" instead of "if (zone->spanned_pages)".
Simplify the code, no functional change.
Signed-off-by: NXishi Qiu <qiuxishi@huawei.com>
Cc: Cody P Schafer <cody@linux.vnet.ibm.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Use "zone_end_pfn()" instead of "zone->zone_start_pfn + zone->spanned_pages".
Simplify the code, no functional change.

[akpm@linux-foundation.org: fix build]
Signed-off-by: NXishi Qiu <qiuxishi@huawei.com>
Cc: Cody P Schafer <cody@linux.vnet.ibm.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

In struct gen_pool_chunk, end_addr means the end address of memory chunk
(inclusive), but in the implementation it is treated as address + size of
memory chunk (exclusive), so it points to the address plus one instead of
correct ending address.

The ending address of memory chunk plus one will cause overflow on the
memory chunk including the last address of memory map, e.g.  when starting
address is 0xFFF00000 and size is 0x100000 on 32bit machine, ending
address will be 0x100000000.

Use correct ending address like starting address + size - 1.

[akpm@linux-foundation.org: add comment to struct gen_pool_chunk:end_addr]
Signed-off-by: NJoonyoung Shim <jy0922.shim@samsung.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Signed-off-by: NJianguo Wu <wujianguo@huawei.com>
Cc: Seth Jennings <sjenning@linux.vnet.ibm.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

I think we can remove "BUG_ON(start_pfn >= end_pfn)" in __offline_pages(),
because in memory_block_action() "nr_pages = PAGES_PER_SECTION * sections_per_block"
is always greater than 0.

memory_block_action()
	offline_pages()
		__offline_pages()
			BUG_ON(start_pfn >= end_pfn)

In v2.6.32, If info->length==0, this way may hit this BUG_ON().
acpi_memory_disable_device()
	remove_memory(info->start_addr, info->length)
			offline_pages()

A later Fujitsu patch renamed this function and the BUG_ON() is
unnecessary.
Signed-off-by: NXishi Qiu <qiuxishi@huawei.com>
Reviewed-by: NDave Hansen <dave.hansen@linux.intel.com>
Cc: Toshi Kani <toshi.kani@hp.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Our intention in here is to find last_bit within the region to flush.
There is well-defined function, find_last_bit() for this purpose and its
performance may be slightly better than current implementation.  So change
it.
Signed-off-by: NJoonsoo Kim <iamjoonsoo.kim@lge.com>
Reviewed-by: NWanpeng Li <liwanp@linux.vnet.ibm.com>
Acked-by: NJohannes Weiner <hannes@cmpxchg.org>
Acked-by: NZhang Yanfei <zhangyanfei@cn.fujitsu.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

vbq in vmap_block isn't used. So remove it.
Signed-off-by: NJoonsoo Kim <iamjoonsoo.kim@lge.com>
Reviewed-by: NWanpeng Li <liwanp@linux.vnet.ibm.com>
Acked-by: NJohannes Weiner <hannes@cmpxchg.org>
Acked-by: NZhang Yanfei <zhangyanfei@cn.fujitsu.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Disabling interrupts repeatedly can be avoided in the inner loop if we use
a this_cpu operation.
Signed-off-by: NChristoph Lameter <cl@linux.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
CC: Tejun Heo <tj@kernel.org>
Cc: Joonsoo Kim <js1304@gmail.com>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Both functions that update global counters use the same mechanism.

Create a function that contains the common code.
Signed-off-by: NChristoph Lameter <cl@linux.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
CC: Tejun Heo <tj@kernel.org>
Cc: Joonsoo Kim <js1304@gmail.com>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

The main idea behind this patchset is to reduce the vmstat update overhead
by avoiding interrupt enable/disable and the use of per cpu atomics.

This patch (of 3):

It is better to have a separate folding function because
refresh_cpu_vm_stats() also does other things like expire pages in the
page allocator caches.

If we have a separate function then refresh_cpu_vm_stats() is only called
from the local cpu which allows additional optimizations.

The folding function is only called when a cpu is being downed and
therefore no other processor will be accessing the counters.  Also
simplifies synchronization.

[akpm@linux-foundation.org: fix UP build]
Signed-off-by: NChristoph Lameter <cl@linux.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
CC: Tejun Heo <tj@kernel.org>
Cc: Joonsoo Kim <js1304@gmail.com>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

PageSwapCache() is always false when !CONFIG_SWAP, so compiler
properly discard related code. Therefore, we don't need #ifdef explicitly.
Signed-off-by: NJoonsoo Kim <iamjoonsoo.kim@lge.com>
Acked-by: NJohannes Weiner <hannes@cmpxchg.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

pgtable related functions are mostly in pgtable-generic.c.
So move remaining functions from memory.c to pgtable-generic.c.
Signed-off-by: NJoonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

We rarely allocate a page with ALLOC_NO_WATERMARKS and it is used in slow
path.  For helping compiler optimization, add unlikely macro to
ALLOC_NO_WATERMARKS checking.

This patch doesn't have any effect now, because gcc already optimize this
properly.  But we cannot assume that gcc always does right and nobody
re-evaluate if gcc do proper optimization with their change, for example,
it is not optimized properly on v3.10.  So adding compiler hint here is
reasonable.
Signed-off-by: NJoonsoo Kim <iamjoonsoo.kim@lge.com>
Acked-by: NJohannes Weiner <hannes@cmpxchg.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

If node == NUMA_NO_NODE, pol is NULL, we should return NULL instead of
do "if (!pol->mode)" check.

[akpm@linux-foundation.org: reorganise code]
Signed-off-by: NJianguo Wu <wujianguo@huawei.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Hanjun Guo <guohanjun@huawei.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

If a vma with VM_NORESERVE allocate a new page for page cache, we should
check whether this area is reserved or not.  If this address is already
reserved by other process(in case of chg == 0), we should decrement
reserve count, because this allocated page will go into page cache and
currently, there is no way to know that this page comes from reserved pool
or not when releasing inode.  This may introduce over-counting problem to
reserved count.  With following example code, you can easily reproduce
this situation.

Assume 2MB, nr_hugepages = 100

        size = 20 * MB;
        flag = MAP_SHARED;
        p = mmap(NULL, size, PROT_READ|PROT_WRITE, flag, fd, 0);
        if (p == MAP_FAILED) {
                fprintf(stderr, "mmap() failed: %s\n", strerror(errno));
                return -1;
        }

        flag = MAP_SHARED | MAP_NORESERVE;
        q = mmap(NULL, size, PROT_READ|PROT_WRITE, flag, fd, 0);
        if (q == MAP_FAILED) {
                fprintf(stderr, "mmap() failed: %s\n", strerror(errno));
        }
        q[0] = 'c';

After finish the program, run 'cat /proc/meminfo'.  You can see below
result.

HugePages_Free:      100
HugePages_Rsvd:        1

To fix this, we should check our mapping type and tracked region.  If our
mapping is VM_NORESERVE, VM_MAYSHARE and chg is 0, this imply that current
allocated page will go into page cache which is already reserved region
when mapping is created.  In this case, we should decrease reserve count.
As implementing above, this patch solve the problem.

[akpm@linux-foundation.org: fix spelling in comment]
Signed-off-by: NJoonsoo Kim <iamjoonsoo.kim@lge.com>
Reviewed-by: NWanpeng Li <liwanp@linux.vnet.ibm.com>
Reviewed-by: NAneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Acked-by: NHillf Danton <dhillf@gmail.com>
Acked-by: NMichal Hocko <mhocko@suse.cz>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Davidlohr Bueso <davidlohr.bueso@hp.com>
Cc: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Now, Checking condition of decrement_hugepage_resv_vma() and
vma_has_reserves() is same, so we can clean-up this function with
vma_has_reserves().  Additionally, decrement_hugepage_resv_vma() has only
one call site, so we can remove function and embed it into
dequeue_huge_page_vma() directly.  This patch implement it.
Signed-off-by: NJoonsoo Kim <iamjoonsoo.kim@lge.com>
Reviewed-by: NWanpeng Li <liwanp@linux.vnet.ibm.com>
Reviewed-by: NAneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Acked-by: NHillf Danton <dhillf@gmail.com>
Acked-by: NMichal Hocko <mhocko@suse.cz>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Davidlohr Bueso <davidlohr.bueso@hp.com>
Cc: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

If we map the region with MAP_NORESERVE and MAP_SHARED, we can skip to
check reserve counting and eventually we cannot be ensured to allocate a
huge page in fault time.  With following example code, you can easily find
this situation.

Assume 2MB, nr_hugepages = 100

        fd = hugetlbfs_unlinked_fd();
        if (fd < 0)
                return 1;

        size = 200 * MB;
        flag = MAP_SHARED;
        p = mmap(NULL, size, PROT_READ|PROT_WRITE, flag, fd, 0);
        if (p == MAP_FAILED) {
                fprintf(stderr, "mmap() failed: %s\n", strerror(errno));
                return -1;
        }

        size = 2 * MB;
        flag = MAP_ANONYMOUS | MAP_SHARED | MAP_HUGETLB | MAP_NORESERVE;
        p = mmap(NULL, size, PROT_READ|PROT_WRITE, flag, -1, 0);
        if (p == MAP_FAILED) {
                fprintf(stderr, "mmap() failed: %s\n", strerror(errno));
        }
        p[0] = '0';
        sleep(10);

During executing sleep(10), run 'cat /proc/meminfo' on another process.

HugePages_Free:       99
HugePages_Rsvd:      100

Number of free should be higher or equal than number of reserve, but this
aren't.  This represent that non reserved shared mapping steal a reserved
page.  Non reserved shared mapping should not eat into reserve space.

If we consider VM_NORESERVE in vma_has_reserve() and return 0 which mean
that we don't have reserved pages, then we check that we have enough free
pages in dequeue_huge_page_vma().  This prevent to steal a reserved page.

With this change, above test generate a SIGBUG which is correct, because
all free pages are reserved and non reserved shared mapping can't get a
free page.
Signed-off-by: NJoonsoo Kim <iamjoonsoo.kim@lge.com>
Reviewed-by: NWanpeng Li <liwanp@linux.vnet.ibm.com>
Reviewed-by: NAneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Acked-by: NHillf Danton <dhillf@gmail.com>
Acked-by: NMichal Hocko <mhocko@suse.cz>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Davidlohr Bueso <davidlohr.bueso@hp.com>
Cc: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Currently, we use a page with mapped count 1 in page cache for cow
optimization.  If we find this condition, we don't allocate a new page and
copy contents.  Instead, we map this page directly.  This may introduce a
problem that writting to private mapping overwrite hugetlb file directly.
You can find this situation with following code.

        size = 20 * MB;
        flag = MAP_SHARED;
        p = mmap(NULL, size, PROT_READ|PROT_WRITE, flag, fd, 0);
        if (p == MAP_FAILED) {
                fprintf(stderr, "mmap() failed: %s\n", strerror(errno));
                return -1;
        }
        p[0] = 's';
        fprintf(stdout, "BEFORE STEAL PRIVATE WRITE: %c\n", p[0]);
        munmap(p, size);

        flag = MAP_PRIVATE;
        p = mmap(NULL, size, PROT_READ|PROT_WRITE, flag, fd, 0);
        if (p == MAP_FAILED) {
                fprintf(stderr, "mmap() failed: %s\n", strerror(errno));
        }
        p[0] = 'c';
        munmap(p, size);

        flag = MAP_SHARED;
        p = mmap(NULL, size, PROT_READ|PROT_WRITE, flag, fd, 0);
        if (p == MAP_FAILED) {
                fprintf(stderr, "mmap() failed: %s\n", strerror(errno));
                return -1;
        }
        fprintf(stdout, "AFTER STEAL PRIVATE WRITE: %c\n", p[0]);
        munmap(p, size);

We can see that "AFTER STEAL PRIVATE WRITE: c", not "AFTER STEAL PRIVATE
WRITE: s".  If we turn off this optimization to a page in page cache, the
problem is disappeared.

So, I change the trigger condition of optimization.  If this page is not
AnonPage, we don't do optimization.  This makes this optimization turning
off for a page cache.
Signed-off-by: NJoonsoo Kim <iamjoonsoo.kim@lge.com>
Acked-by: NMichal Hocko <mhocko@suse.cz>
Reviewed-by: NWanpeng Li <liwanp@linux.vnet.ibm.com>
Reviewed-by: NNaoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Acked-by: NHillf Danton <dhillf@gmail.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Davidlohr Bueso <davidlohr.bueso@hp.com>
Cc: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

If list is empty, list_for_each_entry_safe() doesn't do anything.  So,
this check is redundant.  Remove it.
Signed-off-by: NJoonsoo Kim <iamjoonsoo.kim@lge.com>
Acked-by: NMichal Hocko <mhocko@suse.cz>
Reviewed-by: NWanpeng Li <liwanp@linux.vnet.ibm.com>
Reviewed-by: NAneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Acked-by: NHillf Danton <dhillf@gmail.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Wanpeng Li <liwanp@linux.vnet.ibm.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Davidlohr Bueso <davidlohr.bueso@hp.com>
Cc: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Current node iteration code have a minor problem which do one more node
rotation if we can't succeed to allocate.  For example, if we start to
allocate at node 0, we stop to iterate at node 0.  Then we start to
allocate at node 1 for next allocation.

I introduce new macros "for_each_node_mask_to_[alloc|free]" and fix and
clean-up node iteration code to alloc or free.  This makes code more
understandable.
Signed-off-by: NJoonsoo Kim <iamjoonsoo.kim@lge.com>
Reviewed-by: NAneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Acked-by: NHillf Danton <dhillf@gmail.com>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Wanpeng Li <liwanp@linux.vnet.ibm.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Davidlohr Bueso <davidlohr.bueso@hp.com>
Cc: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Unify successful allocation paths to make the code more readable.  There
are no functional changes.
Signed-off-by: NJoonsoo Kim <iamjoonsoo.kim@lge.com>
Acked-by: NMichal Hocko <mhocko@suse.cz>
Reviewed-by: NWanpeng Li <liwanp@linux.vnet.ibm.com>
Reviewed-by: NAneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Cc: Hillf Danton <dhillf@gmail.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Wanpeng Li <liwanp@linux.vnet.ibm.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Davidlohr Bueso <davidlohr.bueso@hp.com>
Cc: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

The name of the mutex written in comment is wrong.  Fix it.
Signed-off-by: NJoonsoo Kim <iamjoonsoo.kim@lge.com>
Acked-by: NMichal Hocko <mhocko@suse.cz>
Acked-by: NHillf Danton <dhillf@gmail.com>
Reviewed-by: NAneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Cc: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Wanpeng Li <liwanp@linux.vnet.ibm.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Davidlohr Bueso <davidlohr.bueso@hp.com>
Cc: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

In this time we are holding a hugetlb_lock, so hstate values can't be
changed.  If we don't have any usable free huge page in this time, we
don't need to proceed with the processing.  So move this code up.
Signed-off-by: NJoonsoo Kim <iamjoonsoo.kim@lge.com>
Acked-by: NMichal Hocko <mhocko@suse.cz>
Reviewed-by: NWanpeng Li <liwanp@linux.vnet.ibm.com>
Reviewed-by: NAneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Cc: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Acked-by: NHillf Danton <dhillf@gmail.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Davidlohr Bueso <davidlohr.bueso@hp.com>
Cc: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

This reverts commit 75f7ad8e.  It was the result of a problem
observed with a 3.2 kernel and merged in 3.9, while the issue had been
resolved upstream in 3.3 (commit ab8fabd4: "mm: exclude reserved
pages from dirtyable memory").

The "reserved pages" are a superset of min_free_kbytes, thus this change
is redundant and confusing.  Revert it.
Signed-off-by: NJohannes Weiner <hannes@cmpxchg.org>
Cc: Paul Szabo <psz@maths.usyd.edu.au>
Cc: Rik van Riel <riel@redhat.com>
Acked-by: NMinchan Kim <minchan@kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Each zone that holds userspace pages of one workload must be aged at a
speed proportional to the zone size.  Otherwise, the time an individual
page gets to stay in memory depends on the zone it happened to be
allocated in.  Asymmetry in the zone aging creates rather unpredictable
aging behavior and results in the wrong pages being reclaimed, activated
etc.

But exactly this happens right now because of the way the page allocator
and kswapd interact.  The page allocator uses per-node lists of all zones
in the system, ordered by preference, when allocating a new page.  When
the first iteration does not yield any results, kswapd is woken up and the
allocator retries.  Due to the way kswapd reclaims zones below the high
watermark while a zone can be allocated from when it is above the low
watermark, the allocator may keep kswapd running while kswapd reclaim
ensures that the page allocator can keep allocating from the first zone in
the zonelist for extended periods of time.  Meanwhile the other zones
rarely see new allocations and thus get aged much slower in comparison.

The result is that the occasional page placed in lower zones gets
relatively more time in memory, even gets promoted to the active list
after its peers have long been evicted.  Meanwhile, the bulk of the
working set may be thrashing on the preferred zone even though there may
be significant amounts of memory available in the lower zones.

Even the most basic test -- repeatedly reading a file slightly bigger than
memory -- shows how broken the zone aging is.  In this scenario, no single
page should be able stay in memory long enough to get referenced twice and
activated, but activation happens in spades:

  $ grep active_file /proc/zoneinfo
      nr_inactive_file 0
      nr_active_file 0
      nr_inactive_file 0
      nr_active_file 8
      nr_inactive_file 1582
      nr_active_file 11994
  $ cat data data data data >/dev/null
  $ grep active_file /proc/zoneinfo
      nr_inactive_file 0
      nr_active_file 70
      nr_inactive_file 258753
      nr_active_file 443214
      nr_inactive_file 149793
      nr_active_file 12021

Fix this with a very simple round robin allocator.  Each zone is allowed a
batch of allocations that is proportional to the zone's size, after which
it is treated as full.  The batch counters are reset when all zones have
been tried and the allocator enters the slowpath and kicks off kswapd
reclaim.  Allocation and reclaim is now fairly spread out to all
available/allowable zones:

  $ grep active_file /proc/zoneinfo
      nr_inactive_file 0
      nr_active_file 0
      nr_inactive_file 174
      nr_active_file 4865
      nr_inactive_file 53
      nr_active_file 860
  $ cat data data data data >/dev/null
  $ grep active_file /proc/zoneinfo
      nr_inactive_file 0
      nr_active_file 0
      nr_inactive_file 666622
      nr_active_file 4988
      nr_inactive_file 190969
      nr_active_file 937

When zone_reclaim_mode is enabled, allocations will now spread out to all
zones on the local node, not just the first preferred zone (which on a 4G
node might be a tiny Normal zone).
Signed-off-by: NJohannes Weiner <hannes@cmpxchg.org>
Acked-by: NMel Gorman <mgorman@suse.de>
Reviewed-by: NRik van Riel <riel@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Paul Bolle <paul.bollee@gmail.com>
Cc: Zlatko Calusic <zcalusic@bitsync.net>
Tested-by: NKevin Hilman <khilman@linaro.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Allocations that do not have to respect the watermarks are rare
high-priority events.  Reorder the code such that per-zone dirty limits
and future checks important only to regular page allocations are ignored
in these extraordinary situations.
Signed-off-by: NJohannes Weiner <hannes@cmpxchg.org>
Cc: Mel Gorman <mgorman@suse.de>
Reviewed-by: NRik van Riel <riel@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Paul Bolle <paul.bollee@gmail.com>
Tested-by: NZlatko Calusic <zcalusic@bitsync.net>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

The way the page allocator interacts with kswapd creates aging imbalances,
where the amount of time a userspace page gets in memory under reclaim
pressure is dependent on which zone, which node the allocator took the
page frame from.

#1 fixes missed kswapd wakeups on NUMA systems, which lead to some
   nodes falling behind for a full reclaim cycle relative to the other
   nodes in the system

#3 fixes an interaction where kswapd and a continuous stream of page
   allocations keep the preferred zone of a task between the high and
   low watermark (allocations succeed + kswapd does not go to sleep)
   indefinitely, completely underutilizing the lower zones and
   thrashing on the preferred zone

These patches are the aging fairness part of the thrash-detection based
file LRU balancing.  Andrea recommended to submit them separately as they
are bugfixes in their own right.

The following test ran a foreground workload (memcachetest) with
background IO of various sizes on a 4 node 8G system (similar results were
observed with single-node 4G systems):

parallelio
                                               BAS                    FAIRALLO
                                              BASE                   FAIRALLOC
Ops memcachetest-0M              5170.00 (  0.00%)           5283.00 (  2.19%)
Ops memcachetest-791M            4740.00 (  0.00%)           5293.00 ( 11.67%)
Ops memcachetest-2639M           2551.00 (  0.00%)           4950.00 ( 94.04%)
Ops memcachetest-4487M           2606.00 (  0.00%)           3922.00 ( 50.50%)
Ops io-duration-0M                  0.00 (  0.00%)              0.00 (  0.00%)
Ops io-duration-791M               55.00 (  0.00%)             18.00 ( 67.27%)
Ops io-duration-2639M             235.00 (  0.00%)            103.00 ( 56.17%)
Ops io-duration-4487M             278.00 (  0.00%)            173.00 ( 37.77%)
Ops swaptotal-0M                    0.00 (  0.00%)              0.00 (  0.00%)
Ops swaptotal-791M             245184.00 (  0.00%)              0.00 (  0.00%)
Ops swaptotal-2639M            468069.00 (  0.00%)         108778.00 ( 76.76%)
Ops swaptotal-4487M            452529.00 (  0.00%)          76623.00 ( 83.07%)
Ops swapin-0M                       0.00 (  0.00%)              0.00 (  0.00%)
Ops swapin-791M                108297.00 (  0.00%)              0.00 (  0.00%)
Ops swapin-2639M               169537.00 (  0.00%)          50031.00 ( 70.49%)
Ops swapin-4487M               167435.00 (  0.00%)          34178.00 ( 79.59%)
Ops minorfaults-0M            1518666.00 (  0.00%)        1503993.00 (  0.97%)
Ops minorfaults-791M          1676963.00 (  0.00%)        1520115.00 (  9.35%)
Ops minorfaults-2639M         1606035.00 (  0.00%)        1799717.00 (-12.06%)
Ops minorfaults-4487M         1612118.00 (  0.00%)        1583825.00 (  1.76%)
Ops majorfaults-0M                  6.00 (  0.00%)              0.00 (  0.00%)
Ops majorfaults-791M            13836.00 (  0.00%)             10.00 ( 99.93%)
Ops majorfaults-2639M           22307.00 (  0.00%)           6490.00 ( 70.91%)
Ops majorfaults-4487M           21631.00 (  0.00%)           4380.00 ( 79.75%)

                 BAS    FAIRALLO
                BASE   FAIRALLOC
User          287.78      460.97
System       2151.67     3142.51
Elapsed      9737.00     8879.34

                                   BAS    FAIRALLO
                                  BASE   FAIRALLOC
Minor Faults                  53721925    57188551
Major Faults                    392195       15157
Swap Ins                       2994854      112770
Swap Outs                      4907092      134982
Direct pages scanned                 0       41824
Kswapd pages scanned          32975063     8128269
Kswapd pages reclaimed         6323069     7093495
Direct pages reclaimed               0       41824
Kswapd efficiency                  19%         87%
Kswapd velocity               3386.573     915.414
Direct efficiency                 100%        100%
Direct velocity                  0.000       4.710
Percentage direct scans             0%          0%
Zone normal velocity          2011.338     550.661
Zone dma32 velocity           1365.623     369.221
Zone dma velocity                9.612       0.242
Page writes by reclaim    18732404.000  614807.000
Page writes file              13825312      479825
Page writes anon               4907092      134982
Page reclaim immediate           85490        5647
Sector Reads                  12080532      483244
Sector Writes                 88740508    65438876
Page rescued immediate               0           0
Slabs scanned                    82560       12160
Direct inode steals                  0           0
Kswapd inode steals              24401       40013
Kswapd skipped wait                  0           0
THP fault alloc                      6           8
THP collapse alloc                5481        5812
THP splits                          75          22
THP fault fallback                   0           0
THP collapse fail                    0           0
Compaction stalls                    0          54
Compaction success                   0          45
Compaction failures                  0           9
Page migrate success            881492       82278
Page migrate failure                 0           0
Compaction pages isolated            0       60334
Compaction migrate scanned           0       53505
Compaction free scanned              0     1537605
Compaction cost                    914          86
NUMA PTE updates              46738231    41988419
NUMA hint faults              31175564    24213387
NUMA hint local faults        10427393     6411593
NUMA pages migrated             881492       55344
AutoNUMA cost                   156221      121361

The overall runtime was reduced, throughput for both the foreground
workload as well as the background IO improved, major faults, swapping and
reclaim activity shrunk significantly, reclaim efficiency more than
quadrupled.

This patch:

When the page allocator fails to get a page from all zones in its given
zonelist, it wakes up the per-node kswapds for all zones that are at their
low watermark.

However, with a system under load the free pages in a zone can fluctuate
enough that the allocation fails but the kswapd wakeup is also skipped
while the zone is still really close to the low watermark.

When one node misses a wakeup like this, it won't be aged before all the
other node's zones are down to their low watermarks again.  And skipping a
full aging cycle is an obvious fairness problem.

Kswapd runs until the high watermarks are restored, so it should also be
woken when the high watermarks are not met.  This ages nodes more equally
and creates a safety margin for the page counter fluctuation.

By using zone_balanced(), it will now check, in addition to the watermark,
if compaction requires more order-0 pages to create a higher order page.
Signed-off-by: NJohannes Weiner <hannes@cmpxchg.org>
Cc: Mel Gorman <mgorman@suse.de>
Reviewed-by: NRik van Riel <riel@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Paul Bolle <paul.bollee@gmail.com>
Tested-by: NZlatko Calusic <zcalusic@bitsync.net>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

In collapse_huge_page() there is a race window between releasing the
mmap_sem read lock and taking the mmap_sem write lock, so find_vma() may
return NULL.  So check the return value to avoid NULL pointer dereference.

collapse_huge_page
	khugepaged_alloc_page
		up_read(&mm->mmap_sem)
	down_write(&mm->mmap_sem)
	vma = find_vma(mm, address)
Signed-off-by: NLibin <huawei.libin@huawei.com>
Acked-by: NKirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reviewed-by: NWanpeng Li <liwanp@linux.vnet.ibm.com>
Reviewed-by: NMichal Hocko <mhocko@suse.cz>
Cc: <stable@vger.kernel.org> # v3.0+
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

We should not check loop+1 with loop end in loop body.  Just duplicate two
lines code to avoid it.

That will help a bit when we have huge amount of pages on system with
16TiB memory.
Signed-off-by: NYinghai Lu <yinghai@kernel.org>
Cc: Mel Gorman <mgorman@suse.de>
Acked-by: NJohannes Weiner <hannes@cmpxchg.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

In the current code, the value of fallback_migratetype that is printed
using the mm_page_alloc_extfrag tracepoint, is the value of the
migratetype *after* it has been set to the preferred migratetype (if the
ownership was changed).  Obviously that wouldn't have been the original
intent.  (We already have a separate 'change_ownership' field to tell
whether the ownership of the pageblock was changed from the
fallback_migratetype to the preferred type.)

The intent of the fallback_migratetype field is to show the migratetype
from which we borrowed pages in order to satisfy the allocation request.
So fix the code to print that value correctly.
Signed-off-by: NSrivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Cody P Schafer <cody@linux.vnet.ibm.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

The free-page stealing code in __rmqueue_fallback() is somewhat hard to
follow, and has an incredible amount of subtlety hidden inside!

First off, there is a minor bug in the reporting of change-of-ownership of
pageblocks.  Under some conditions, we try to move upto
'pageblock_nr_pages' no.  of pages to the preferred allocation list.  But
we change the ownership of that pageblock to the preferred type only if we
manage to successfully move atleast half of that pageblock (or if
page_group_by_mobility_disabled is set).

However, the current code ignores the latter part and sets the
'migratetype' variable to the preferred type, irrespective of whether we
actually changed the pageblock migratetype of that block or not.  So, the
page_alloc_extfrag tracepoint can end up printing incorrect info (i.e.,
'change_ownership' might be shown as 1 when it must have been 0).

So fixing this involves moving the update of the 'migratetype' variable to
the right place.  But looking closer, we observe that the 'migratetype'
variable is used subsequently for checks such as "is_migrate_cma()".
Obviously the intent there is to check if the *fallback* type is
MIGRATE_CMA, but since we already set the 'migratetype' variable to
start_migratetype, we end up checking if the *preferred* type is
MIGRATE_CMA!!

To make things more interesting, this actually doesn't cause a bug in
practice, because we never change *anything* if the fallback type is CMA.

So, restructure the code in such a way that it is trivial to understand
what is going on, and also fix the above mentioned bug.  And while at it,
also add a comment explaining the subtlety behind the migratetype used in
the call to expand().

[akpm@linux-foundation.org: remove unneeded `inline', small coding-style fix]
Signed-off-by: NSrivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Cody P Schafer <cody@linux.vnet.ibm.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>