linux-stable.git/mm/page_alloc.c, branch v3.7

Revert "revert "Revert "mm: remove __GFP_NO_KSWAPD""" and associated damage

2012-12-10T19:03:05+00:00

This reverts commits a50915394f1fc02c2861d3b7ce7014788aa5066e and
d7c3b937bdf45f0b844400b7bf6fd3ed50bac604.

This is a revert of a revert of a revert.  In addition, it reverts the
even older i915 change to stop using the __GFP_NO_KSWAPD flag due to the
original commits in linux-next.

It turns out that the original patch really was bogus, and that the
original revert was the correct thing to do after all.  We thought we
had fixed the problem, and then reverted the revert, but the problem
really is fundamental: waking up kswapd simply isn't the right thing to
do, and direct reclaim sometimes simply _is_ the right thing to do.

When certain allocations fail, we simply should try some direct reclaim,
and if that fails, fail the allocation.  That's the right thing to do
for THP allocations, which can easily fail, and the GPU allocations want
to do that too.

So starting kswapd is sometimes simply wrong, and removing the flag that
said "don't start kswapd" was a mistake.  Let's hope we never revisit
this mistake again - and certainly not this many times ;)

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

Revert "mm: avoid waking kswapd for THP allocations when compaction is deferred or contended"

2012-12-10T18:47:45+00:00

This reverts commit 782fd30406ecb9d9b082816abe0c6008fc72a7b0.

We are going to reinstate the __GFP_NO_KSWAPD flag that has been
removed, the removal reverted, and then removed again.  Making this
commit a pointless fixup for a problem that was caused by the removal of
__GFP_NO_KSWAPD flag.

The thing is, we really don't want to wake up kswapd for THP allocations
(because they fail quite commonly under any kind of memory pressure,
including when there is tons of memory free), and these patches were
just trying to fix up the underlying bug: the original removal of
__GFP_NO_KSWAPD in commit c654345924f7 ("mm: remove __GFP_NO_KSWAPD")
was simply bogus.

Signed-off-by: Linus Torvalds

mm: avoid waking kswapd for THP allocations when compaction is deferred or contended

2012-11-30T16:51:18+00:00

With "mm: vmscan: scale number of pages reclaimed by reclaim/compaction
based on failures" reverted, Zdenek Kabelac reported the following

  Hmm,  so it's just took longer to hit the problem and observe
  kswapd0 spinning on my CPU again - it's not as endless like before -
  but still it easily eats minutes - it helps to turn off  Firefox
  or TB  (memory hungry apps) so kswapd0 stops soon - and restart
  those apps again.  (And I still have like >1GB of cached memory)

  kswapd0         R  running task        0    30      2 0x00000000
  Call Trace:
    preempt_schedule+0x42/0x60
    _raw_spin_unlock+0x55/0x60
    put_super+0x31/0x40
    drop_super+0x22/0x30
    prune_super+0x149/0x1b0
    shrink_slab+0xba/0x510

The sysrq+m indicates the system has no swap so it'll never reclaim
anonymous pages as part of reclaim/compaction.  That is one part of the
problem but not the root cause as file-backed pages could also be
reclaimed.

The likely underlying problem is that kswapd is woken up or kept awake
for each THP allocation request in the page allocator slow path.

If compaction fails for the requesting process then compaction will be
deferred for a time and direct reclaim is avoided.  However, if there
are a storm of THP requests that are simply rejected, it will still be
the the case that kswapd is awake for a prolonged period of time as
pgdat->kswapd_max_order is updated each time.  This is noticed by the
main kswapd() loop and it will not call kswapd_try_to_sleep().  Instead
it will loopp, shrinking a small number of pages and calling
shrink_slab() on each iteration.

This patch defers when kswapd gets woken up for THP allocations.  For
!THP allocations, kswapd is always woken up.  For THP allocations,
kswapd is woken up iff the process is willing to enter into direct
reclaim/compaction.

[akpm@linux-foundation.org: fix typo in comment]
Signed-off-by: Mel Gorman 
Cc: Zdenek Kabelac 
Cc: Seth Jennings 
Cc: Jiri Slaby 
Cc: Rik van Riel 
Cc: Robert Jennings 
Cc: Valdis Kletnieks 
Cc: Glauber Costa 
Cc: Johannes Weiner 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

revert "Revert "mm: remove __GFP_NO_KSWAPD""

2012-11-30T16:51:17+00:00

It apepars that this patch was innocent, and we hope that "mm: avoid
waking kswapd for THP allocations when compaction is deferred or
contended" will fix the final kswapd-spinning cause.

Cc: Zdenek Kabelac 
Cc: Seth Jennings 
Cc: Valdis Kletnieks 
Cc: Jiri Slaby 
Cc: Rik van Riel 
Cc: Robert Jennings 
Cc: Mel Gorman 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm: compaction: fix return value of capture_free_page()

2012-11-30T16:51:17+00:00

Commit ef6c5be658f6 ("fix incorrect NR_FREE_PAGES accounting (appears
like memory leak)") fixes a NR_FREE_PAGE accounting leak but missed the
return value which was also missed by this reviewer until today.

That return value is used by compaction when adding pages to a list of
isolated free pages and without this follow-up fix, there is a risk of
free list corruption.

Signed-off-by: Mel Gorman 
Cc: Dave Hansen 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

Revert "mm: remove __GFP_NO_KSWAPD"

2012-11-27T01:41:24+00:00

With "mm: vmscan: scale number of pages reclaimed by reclaim/compaction
based on failures" reverted, Zdenek Kabelac reported the following

  Hmm,  so it's just took longer to hit the problem and observe
  kswapd0 spinning on my CPU again - it's not as endless like before -
  but still it easily eats minutes - it helps to	turn off  Firefox
  or TB  (memory hungry apps) so kswapd0 stops soon - and restart
  those apps again.  (And I still have like >1GB of cached memory)

  kswapd0         R  running task        0    30      2 0x00000000
  Call Trace:
    preempt_schedule+0x42/0x60
    _raw_spin_unlock+0x55/0x60
    put_super+0x31/0x40
    drop_super+0x22/0x30
    prune_super+0x149/0x1b0
    shrink_slab+0xba/0x510

The sysrq+m indicates the system has no swap so it'll never reclaim
anonymous pages as part of reclaim/compaction.  That is one part of the
problem but not the root cause as file-backed pages could also be
reclaimed.

The likely underlying problem is that kswapd is woken up or kept awake
for each THP allocation request in the page allocator slow path.

If compaction fails for the requesting process then compaction will be
deferred for a time and direct reclaim is avoided.  However, if there
are a storm of THP requests that are simply rejected, it will still be
the the case that kswapd is awake for a prolonged period of time as
pgdat->kswapd_max_order is updated each time.  This is noticed by the
main kswapd() loop and it will not call kswapd_try_to_sleep().  Instead
it will loopp, shrinking a small number of pages and calling
shrink_slab() on each iteration.

The temptation is to supply a patch that checks if kswapd was woken for
THP and if so ignore pgdat->kswapd_max_order but it'll be a hack and not
backed up by proper testing.  As 3.7 is very close to release and this
is not a bug we should release with, a safer path is to revert "mm:
remove __GFP_NO_KSWAPD" for now and revisit it with the view to ironing
out the balance_pgdat() logic in general.

Signed-off-by: Mel Gorman 
Cc: Zdenek Kabelac 
Cc: Seth Jennings 
Cc: Valdis Kletnieks 
Cc: Jiri Slaby 
Cc: Rik van Riel 
Cc: Robert Jennings 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

fix incorrect NR_FREE_PAGES accounting (appears like memory leak)

2012-11-21T22:33:16+00:00

There have been some 3.7-rc reports of vm issues, including some kswapd
bugs and, more importantly, some memory "leaks":

	http://www.spinics.net/lists/linux-mm/msg46187.html
	https://bugzilla.kernel.org/show_bug.cgi?id=50181

Commit 1fb3f8ca0e92 ("mm: compaction: capture a suitable high-order page
immediately when it is made available") took split_free_page() and
reused it for the compaction code.  It does something curious with
capture_free_page() (previously known as split_free_page()):

  int capture_free_page(struct page *page, int alloc_order,
  ...
          __mod_zone_page_state(zone, NR_FREE_PAGES, -(1UL << order));

  -       /* Split into individual pages */
  -       set_page_refcounted(page);
  -       split_page(page, order);
  +       if (alloc_order != order)
  +               expand(zone, page, alloc_order, order,
  +                       &zone->free_area[order], migratetype);

Note that expand() puts the pages _back_ in the allocator, but it does
not bump NR_FREE_PAGES.  We "return" 'alloc_order' worth of pages, but
we accounted for removing 'order' in the __mod_zone_page_state() call.

For the old split_page()-style use (order==alloc_order) the bug will not
trigger.  But, when called from the compaction code where we
occasionally get a larger page out of the buddy allocator than we need,
we will run in to this.

This patch simply changes the NR_FREE_PAGES manipulation to the correct
'alloc_order' instead of 'order'.

I've been able to repeatedly trigger this in my testing environment.
The amount "leaked" very closely tracks the imbalance I see in buddy
pages vs.  NR_FREE_PAGES.  I have confirmed that this patch fixes the
imbalance

Signed-off-by: Dave Hansen 
Acked-by: Mel Gorman 
Signed-off-by: Linus Torvalds

revert "mm: fix-up zone present pages"

2012-11-16T22:33:04+00:00

Revert commit 7f1290f2f2a4 ("mm: fix-up zone present pages")

That patch tried to fix a issue when calculating zone->present_pages,
but it caused a regression on 32bit systems with HIGHMEM.  With that
change, reset_zone_present_pages() resets all zone->present_pages to
zero, and fixup_zone_present_pages() is called to recalculate
zone->present_pages when the boot allocator frees core memory pages into
buddy allocator.  Because highmem pages are not freed by bootmem
allocator, all highmem zones' present_pages becomes zero.

Various options for improving the situation are being discussed but for
now, let's return to the 3.6 code.

Cc: Jianguo Wu 
Cc: Jiang Liu 
Cc: Petr Tesarik 
Cc: "Luck, Tony" 
Cc: Mel Gorman 
Cc: Yinghai Lu 
Cc: Minchan Kim 
Cc: Johannes Weiner 
Acked-by: David Rientjes 
Tested-by: Chris Clayton 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

memcg: fix hotplugged memory zone oops

2012-11-16T22:33:04+00:00

When MEMCG is configured on (even when it's disabled by boot option),
when adding or removing a page to/from its lru list, the zone pointer
used for stats updates is nowadays taken from the struct lruvec.  (On
many configurations, calculating zone from page is slower.)

But we have no code to update all the lruvecs (per zone, per memcg) when
a memory node is hotadded.  Here's an extract from the oops which
results when running numactl to bind a program to a newly onlined node:

  BUG: unable to handle kernel NULL pointer dereference at 0000000000000f60
  IP:  __mod_zone_page_state+0x9/0x60
  Pid: 1219, comm: numactl Not tainted 3.6.0-rc5+ #180 Bochs Bochs
  Process numactl (pid: 1219, threadinfo ffff880039abc000, task ffff8800383c4ce0)
  Call Trace:
    __pagevec_lru_add_fn+0xdf/0x140
    pagevec_lru_move_fn+0xb1/0x100
    __pagevec_lru_add+0x1c/0x30
    lru_add_drain_cpu+0xa3/0x130
    lru_add_drain+0x2f/0x40
   ...

The natural solution might be to use a memcg callback whenever memory is
hotadded; but that solution has not been scoped out, and it happens that
we do have an easy location at which to update lruvec->zone.  The lruvec
pointer is discovered either by mem_cgroup_zone_lruvec() or by
mem_cgroup_page_lruvec(), and both of those do know the right zone.

So check and set lruvec->zone in those; and remove the inadequate
attempt to set lruvec->zone from lruvec_init(), which is called before
NODE_DATA(node) has been allocated in such cases.

Ah, there was one exceptionr.  For no particularly good reason,
mem_cgroup_force_empty_list() has its own code for deciding lruvec.
Change it to use the standard mem_cgroup_zone_lruvec() and
mem_cgroup_get_lru_size() too.  In fact it was already safe against such
an oops (the lru lists in danger could only be empty), but we're better
proofed against future changes this way.

I've marked this for stable (3.6) since we introduced the problem in 3.5
(now closed to stable); but I have no idea if this is the only fix
needed to get memory hotadd working with memcg in 3.6, and received no
answer when I enquired twice before.

Reported-by: Tang Chen 
Signed-off-by: Hugh Dickins 
Acked-by: Johannes Weiner 
Acked-by: KAMEZAWA Hiroyuki 
Cc: Konstantin Khlebnikov 
Cc: Wen Congyang 
Cc: 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm, numa: avoid setting zone_reclaim_mode unless a node is sufficiently distant

2012-10-25T21:37:53+00:00

Commit 957f822a0ab9 ("mm, numa: reclaim from all nodes within reclaim
distance") caused zone_reclaim_mode to be set for all systems where two
nodes are within RECLAIM_DISTANCE of each other.  This is the opposite
of what we actually want: zone_reclaim_mode should be set if two nodes
are sufficiently distant.

Signed-off-by: David Rientjes 
Reported-by: Julian Wollrath 
Tested-by: Julian Wollrath 
Cc: Hugh Dickins 
Cc: Patrik Kullman 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds