linux-toradex.git/mm/page_alloc.c, branch v3.14.16

mm, thp: do not allow thp faults to avoid cpuset restrictions

2014-08-07T21:52:37+00:00

commit b104a35d32025ca740539db2808aa3385d0f30eb upstream.

The page allocator relies on __GFP_WAIT to determine if ALLOC_CPUSET
should be set in allocflags.  ALLOC_CPUSET controls if a page allocation
should be restricted only to the set of allowed cpuset mems.

Transparent hugepages clears __GFP_WAIT when defrag is disabled to prevent
the fault path from using memory compaction or direct reclaim.  Thus, it
is unfairly able to allocate outside of its cpuset mems restriction as a
side-effect.

This patch ensures that ALLOC_CPUSET is only cleared when the gfp mask is
truly GFP_ATOMIC by verifying it is also not a thp allocation.

Signed-off-by: David Rientjes 
Reported-by: Alex Thorlton 
Tested-by: Alex Thorlton 
Cc: Bob Liu 
Cc: Dave Hansen 
Cc: Hedi Berriche 
Cc: Hugh Dickins 
Cc: Johannes Weiner 
Cc: Kirill A. Shutemov 
Cc: Mel Gorman 
Cc: Rik van Riel 
Cc: Srivatsa S. Bhat 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds 
Signed-off-by: Greg Kroah-Hartman

mm: page_alloc: fix CMA area initialisation when pageblock > MAX_ORDER

2014-07-09T18:18:28+00:00

commit dc78327c0ea7da5186d8cbc1647bd6088c5c9fa5 upstream.

With a kernel configured with ARM64_64K_PAGES && !TRANSPARENT_HUGEPAGE,
the following is triggered at early boot:

  SMP: Total of 8 processors activated.
  devtmpfs: initialized
  Unable to handle kernel NULL pointer dereference at virtual address 00000008
  pgd = fffffe0000050000
  [00000008] *pgd=00000043fba00003, *pmd=00000043fba00003, *pte=00e0000078010407
  Internal error: Oops: 96000006 [#1] SMP
  Modules linked in:
  CPU: 0 PID: 1 Comm: swapper/0 Not tainted 3.15.0-rc864k+ #44
  task: fffffe03bc040000 ti: fffffe03bc080000 task.ti: fffffe03bc080000
  PC is at __list_add+0x10/0xd4
  LR is at free_one_page+0x270/0x638
  ...
  Call trace:
    __list_add+0x10/0xd4
    free_one_page+0x26c/0x638
    __free_pages_ok.part.52+0x84/0xbc
    __free_pages+0x74/0xbc
    init_cma_reserved_pageblock+0xe8/0x104
    cma_init_reserved_areas+0x190/0x1e4
    do_one_initcall+0xc4/0x154
    kernel_init_freeable+0x204/0x2a8
    kernel_init+0xc/0xd4

This happens because init_cma_reserved_pageblock() calls
__free_one_page() with pageblock_order as page order but it is bigger
than MAX_ORDER.  This in turn causes accesses past zone->free_list[].

Fix the problem by changing init_cma_reserved_pageblock() such that it
splits pageblock into individual MAX_ORDER pages if pageblock is bigger
than a MAX_ORDER page.

In cases where !CONFIG_HUGETLB_PAGE_SIZE_VARIABLE, which is all
architectures expect for ia64, powerpc and tile at the moment, the
âpageblock_order > MAX_ORDERâ condition will be optimised out since both
sides of the operator are constants.  In cases where pageblock size is
variable, the performance degradation should not be significant anyway
since init_cma_reserved_pageblock() is called only at boot time at most
MAX_CMA_AREAS times which by default is eight.

Signed-off-by: Michal Nazarewicz 
Reported-by: Mark Salter 
Tested-by: Mark Salter 
Tested-by: Christopher Covington 
Cc: Mel Gorman 
Cc: David Rientjes 
Cc: Marek Szyprowski 
Cc: Catalin Marinas 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds 
Signed-off-by: Greg Kroah-Hartman

mm, pcp: allow restoring percpu_pagelist_fraction default

2014-07-09T18:18:26+00:00

commit 7cd2b0a34ab8e4db971920eef8982f985441adfb upstream.

Oleg reports a division by zero error on zero-length write() to the
percpu_pagelist_fraction sysctl:

    divide error: 0000 [#1] SMP DEBUG_PAGEALLOC
    CPU: 1 PID: 9142 Comm: badarea_io Not tainted 3.15.0-rc2-vm-nfs+ #19
    Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
    task: ffff8800d5aeb6e0 ti: ffff8800d87a2000 task.ti: ffff8800d87a2000
    RIP: 0010: percpu_pagelist_fraction_sysctl_handler+0x84/0x120
    RSP: 0018:ffff8800d87a3e78  EFLAGS: 00010246
    RAX: 0000000000000f89 RBX: ffff88011f7fd000 RCX: 0000000000000000
    RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000010
    RBP: ffff8800d87a3e98 R08: ffffffff81d002c8 R09: ffff8800d87a3f50
    R10: 000000000000000b R11: 0000000000000246 R12: 0000000000000060
    R13: ffffffff81c3c3e0 R14: ffffffff81cfddf8 R15: ffff8801193b0800
    FS:  00007f614f1e9740(0000) GS:ffff88011f440000(0000) knlGS:0000000000000000
    CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
    CR2: 00007f614f1fa000 CR3: 00000000d9291000 CR4: 00000000000006e0
    Call Trace:
      proc_sys_call_handler+0xb3/0xc0
      proc_sys_write+0x14/0x20
      vfs_write+0xba/0x1e0
      SyS_write+0x46/0xb0
      tracesys+0xe1/0xe6

However, if the percpu_pagelist_fraction sysctl is set by the user, it
is also impossible to restore it to the kernel default since the user
cannot write 0 to the sysctl.

This patch allows the user to write 0 to restore the default behavior.
It still requires a fraction equal to or larger than 8, however, as
stated by the documentation for sanity.  If a value in the range [1, 7]
is written, the sysctl will return EINVAL.

This successfully solves the divide by zero issue at the same time.

Signed-off-by: David Rientjes 
Reported-by: Oleg Drokin 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds 
Signed-off-by: Greg Kroah-Hartman

mm: page_alloc: use word-based accesses for get/set pageblock bitmaps

2014-07-01T03:11:53+00:00

commit e58469bafd0524e848c3733bc3918d854595e20f upstream.

The test_bit operations in get/set pageblock flags are expensive.  This
patch reads the bitmap on a word basis and use shifts and masks to isolate
the bits of interest.  Similarly masks are used to set a local copy of the
bitmap and then use cmpxchg to update the bitmap if there have been no
other changes made in parallel.

In a test running dd onto tmpfs the overhead of the pageblock-related
functions went from 1.27% in profiles to 0.5%.

In addition to the performance benefits, this patch closes races that are
possible between:

a) get_ and set_pageblock_migratetype(), where get_pageblock_migratetype()
   reads part of the bits before and other part of the bits after
   set_pageblock_migratetype() has updated them.

b) set_pageblock_migratetype() and set_pageblock_skip(), where the non-atomic
   read-modify-update set bit operation in set_pageblock_skip() will cause
   lost updates to some bits changed in the set_pageblock_migratetype().

Joonsoo Kim first reported the case a) via code inspection.  Vlastimil
Babka's testing with a debug patch showed that either a) or b) occurs
roughly once per mmtests' stress-highalloc benchmark (although not
necessarily in the same pageblock).  Furthermore during development of
unrelated compaction patches, it was observed that frequent calls to
{start,undo}_isolate_page_range() the race occurs several thousands of
times and has resulted in NULL pointer dereferences in move_freepages()
and free_one_page() in places where free_list[migratetype] is
manipulated by e.g.  list_move().  Further debugging confirmed that
migratetype had invalid value of 6, causing out of bounds access to the
free_list array.

That confirmed that the race exist, although it may be extremely rare,
and currently only fatal where page isolation is performed due to
memory hot remove.  Races on pageblocks being updated by
set_pageblock_migratetype(), where both old and new migratetype are
lower MIGRATE_RESERVE, currently cannot result in an invalid value
being observed, although theoretically they may still lead to
unexpected creation or destruction of MIGRATE_RESERVE pageblocks.
Furthermore, things could get suddenly worse when memory isolation is
used more, or when new migratetypes are added.

After this patch, the race has no longer been observed in testing.

Signed-off-by: Mel Gorman 
Acked-by: Vlastimil Babka 
Reported-by: Joonsoo Kim 
Reported-and-tested-by: Vlastimil Babka 
Cc: Johannes Weiner 
Cc: Jan Kara 
Cc: Michal Hocko 
Cc: Hugh Dickins 
Cc: Dave Hansen 
Cc: Theodore Ts'o 
Cc: "Paul E. McKenney" 
Cc: Oleg Nesterov 
Cc: Rik van Riel 
Cc: Peter Zijlstra 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds 
Signed-off-by: Greg Kroah-Hartman

mm: page_alloc: spill to remote nodes before waking kswapd

2014-05-06T14:59:35+00:00

commit 3a025760fc158b3726eac89ee95d7f29599e9dfa upstream.

On NUMA systems, a node may start thrashing cache or even swap anonymous
pages while there are still free pages on remote nodes.

This is a result of commits 81c0a2bb515f ("mm: page_alloc: fair zone
allocator policy") and fff4068cba48 ("mm: page_alloc: revert NUMA aspect
of fair allocation policy").

Before those changes, the allocator would first try all allowed zones,
including those on remote nodes, before waking any kswapds.  But now,
the allocator fastpath doubles as the fairness pass, which in turn can
only consider the local node to prevent remote spilling based on
exhausted fairness batches alone.  Remote nodes are only considered in
the slowpath, after the kswapds are woken up.  But if remote nodes still
have free memory, kswapd should not be woken to rebalance the local node
or it may thrash cash or swap prematurely.

Fix this by adding one more unfair pass over the zonelist that is
allowed to spill to remote nodes after the local fairness pass fails but
before entering the slowpath and waking the kswapds.

This also gets rid of the GFP_THISNODE exemption from the fairness
protocol because the unfair pass is no longer tied to kswapd, which
GFP_THISNODE is not allowed to wake up.

However, because remote spills can be more frequent now - we prefer them
over local kswapd reclaim - the allocation batches on remote nodes could
underflow more heavily.  When resetting the batches, use
atomic_long_read() directly instead of zone_page_state() to calculate the
delta as the latter filters negative counter values.

Signed-off-by: Johannes Weiner 
Acked-by: Rik van Riel 
Acked-by: Mel Gorman 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds 
Signed-off-by: Greg Kroah-Hartman

mm: page_alloc: exempt GFP_THISNODE allocations from zone fairness

2014-03-04T15:55:50+00:00

Jan Stancek reports manual page migration encountering allocation
failures after some pages when there is still plenty of memory free, and
bisected the problem down to commit 81c0a2bb515f ("mm: page_alloc: fair
zone allocator policy").

The problem is that GFP_THISNODE obeys the zone fairness allocation
batches on one hand, but doesn't reset them and wake kswapd on the other
hand.  After a few of those allocations, the batches are exhausted and
the allocations fail.

Fixing this means either having GFP_THISNODE wake up kswapd, or
GFP_THISNODE not participating in zone fairness at all.  The latter
seems safer as an acute bugfix, we can clean up later.

Reported-by: Jan Stancek 
Signed-off-by: Johannes Weiner 
Acked-by: Rik van Riel 
Acked-by: Mel Gorman 
Cc: 		[3.12+]
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm: close PageTail race

2014-03-04T15:55:47+00:00

Commit bf6bddf1924e ("mm: introduce compaction and migration for
ballooned pages") introduces page_count(page) into memory compaction
which dereferences page->first_page if PageTail(page).

This results in a very rare NULL pointer dereference on the
aforementioned page_count(page).  Indeed, anything that does
compound_head(), including page_count() is susceptible to racing with
prep_compound_page() and seeing a NULL or dangling page->first_page
pointer.

This patch uses Andrea's implementation of compound_trans_head() that
deals with such a race and makes it the default compound_head()
implementation.  This includes a read memory barrier that ensures that
if PageTail(head) is true that we return a head page that is neither
NULL nor dangling.  The patch then adds a store memory barrier to
prep_compound_page() to ensure page->first_page is set.

This is the safest way to ensure we see the head page that we are
expecting, PageTail(page) is already in the unlikely() path and the
memory barriers are unfortunately required.

Hugetlbfs is the exception, we don't enforce a store memory barrier
during init since no race is possible.

Signed-off-by: David Rientjes 
Cc: Holger Kiehl 
Cc: Christoph Lameter 
Cc: Rafael Aquini 
Cc: Vlastimil Babka 
Cc: Michal Hocko 
Cc: Mel Gorman 
Cc: Andrea Arcangeli 
Cc: Rik van Riel 
Cc: "Kirill A. Shutemov" 
Cc: 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm: show message when updating min_free_kbytes in thp

2014-01-24T00:36:52+00:00

min_free_kbytes may be raised during THP's initialization.  Sometimes,
this will change the value which was set by the user.  Showing this
message will clarify this confusion.

Only show this message when changing a value which was set by the user
according to Michal Hocko's suggestion.

Show the old value of min_free_kbytes according to Dave Hansen's
suggestion.  This will give user the chance to restore old value of
min_free_kbytes.

Signed-off-by: Han Pingtian 
Reviewed-by: Michal Hocko 
Cc: David Rientjes 
Cc: Mel Gorman 
Cc: Dave Hansen 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm: prevent setting of a value less than 0 to min_free_kbytes

2014-01-24T00:36:52+00:00

If echo -1 > /proc/vm/sys/min_free_kbytes, the system will hang.  Changing
proc_dointvec() to proc_dointvec_minmax() in the
min_free_kbytes_sysctl_handler() can prevent this to happen.

mhocko said:

: You can still do echo $BIG_VALUE > /proc/vm/sys/min_free_kbytes and make
: your machine unusable but I agree that proc_dointvec_minmax is more
: suitable here as we already have:
:
: 	.proc_handler   = min_free_kbytes_sysctl_handler,
: 	.extra1         = &zero,
:
: It used to work properly but then 6fce56ec91b5 ("sysctl: Remove references
: to ctl_name and strategy from the generic sysctl table") has removed
: sysctl_intvec strategy and so extra1 is ignored.

Signed-off-by: Han Pingtian 
Acked-by: Michal Hocko 
Acked-by: David Rientjes 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm: dump page when hitting a VM_BUG_ON using VM_BUG_ON_PAGE

2014-01-24T00:36:50+00:00

Most of the VM_BUG_ON assertions are performed on a page.  Usually, when
one of these assertions fails we'll get a BUG_ON with a call stack and
the registers.

I've recently noticed based on the requests to add a small piece of code
that dumps the page to various VM_BUG_ON sites that the page dump is
quite useful to people debugging issues in mm.

This patch adds a VM_BUG_ON_PAGE(cond, page) which beyond doing what
VM_BUG_ON() does, also dumps the page before executing the actual
BUG_ON.

[akpm@linux-foundation.org: fix up includes]
Signed-off-by: Sasha Levin 
Cc: "Kirill A. Shutemov" 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds