Re: [patch 2/2] fs: buffer: move allocation failure loop into the allocator

Joonsoo Kim
2013-12-04T01:49:52Z

On Tue, Dec 03, 2013 at 04:59:10PM -0800, Andrew Morton wrote:
> On Tue, 8 Oct 2013 16:58:10 -0400 Johannes Weiner <hannes@cmpxchg.org> wrote:
>
> > Buffer allocation has a very crude indefinite loop around waking the
> > flusher threads and performing global NOFS direct reclaim because it
> > can not handle allocation failures.
> >
> > The most immediate problem with this is that the allocation may fail
> > due to a memory cgroup limit, where flushers + direct reclaim might
> > not make any progress towards resolving the situation at all. Because
> > unlike the global case, a memory cgroup may not have any cache at all,
> > only anonymous pages but no swap. This situation will lead to a
> > reclaim livelock with insane IO from waking the flushers and thrashing
> > unrelated filesystem cache in a tight loop.
> >
> > Use __GFP_NOFAIL allocations for buffers for now. This makes sure
> > that any looping happens in the page allocator, which knows how to
> > orchestrate kswapd, direct reclaim, and the flushers sensibly. It
> > also allows memory cgroups to detect allocations that can't handle
> > failure and will allow them to ultimately bypass the limit if reclaim
> > can not make progress.
>
> Problem.
>
> > --- a/fs/buffer.c
> > +++ b/fs/buffer.c
> > @@ -1005,9 +1005,19 @@ grow_dev_page(struct block_device *bdev, sector_t block,
> > struct buffer_head *bh;
> > sector_t end_block;
> > int ret = 0; /* Will call free_more_memory() */
> > + gfp_t gfp_mask;
> >
> > - page = find_or_create_page(inode->i_mapping, index,
> > - (mapping_gfp_mask(inode->i_mapping) & ~__GFP_FS)|__GFP_MOVABLE);
> > + gfp_mask = mapping_gfp_mask(inode->i_mapping) & ~__GFP_FS;
> > + gfp_mask |= __GFP_MOVABLE;
>
> https://bugzilla.kernel.org/show_bug.cgi?id=65991
>
> WARNING: CPU: 0 PID: 1 at mm/page_alloc.c:1539 get_page_from_freelist+0x8a9/0x8c0()
> Modules linked in:
> CPU: 0 PID: 1 Comm: swapper/0 Not tainted 3.13.0-rc1 #42
> Hardware name: Acer Aspire 7750G/JE70_HR, BIOS V1.07 03/02/2011
> 0000000000000009 ffff8801c6121650 ffffffff81898d39 0000000000000000
> ffff8801c6121688 ffffffff8107dc43 0000000000000002 0000000000000001
> 0000000000284850 0000000000000000 ffff8801cec04680 ffff8801c6121698
> Call Trace:
> [<ffffffff81898d39>] dump_stack+0x4e/0x7a
> [<ffffffff8107dc43>] warn_slowpath_common+0x73/0x90
> [<ffffffff8107dd15>] warn_slowpath_null+0x15/0x20
> [<ffffffff81116f69>] get_page_from_freelist+0x8a9/0x8c0
> [<ffffffff81330cdd>] ? trace_hardirqs_off_thunk+0x3a/0x3c
> [<ffffffff81117070>] __alloc_pages_nodemask+0xf0/0x770
> [<ffffffff81330cdd>] ? trace_hardirqs_off_thunk+0x3a/0x3c
> [<ffffffff81156823>] kmemcheck_alloc_shadow+0x53/0xf0
> [<ffffffff81152495>] new_slab+0x345/0x3e0
> [<ffffffff81897712>] __slab_alloc.isra.57+0x215/0x535
> [<ffffffff81328030>] ? __radix_tree_preload+0x60/0xf0
> [<ffffffff811545c8>] kmem_cache_alloc+0x118/0x150
> [<ffffffff81328030>] ? __radix_tree_preload+0x60/0xf0
> [<ffffffff81328030>] __radix_tree_preload+0x60/0xf0
> [<ffffffff81328125>] radix_tree_maybe_preload+0x25/0x30
> [<ffffffff8110faf7>] add_to_page_cache_locked+0x37/0x100
> [<ffffffff8110fbd5>] add_to_page_cache_lru+0x15/0x40
> [<ffffffff8110ff37>] find_or_create_page+0x57/0x90
> [<ffffffff8118e630>] __getblk+0xf0/0x2f0
>
> That __GFP_NOFAIL is getting down into
> radix_tree_preload->kmem_cache_alloc() and I expect that in its
> boundless stupidity, slab has decided to inappropriately go and use an
> unnecessarily massive page size for radix_tree_node_cachep's underlying
> memory allocations. So we end up using GFP_NOFAIL for an order=2 (or
> more) allocation, which is unacceptably risky, methinks.
>
> I really really wish slab wouldn't do this. The benefit is surely very
> small and these unnecessary higher-order allocations are quite abusive
> of the page allocator.
>
> Can we please make slab stop doing this?
>
> radix_tree_nodes are 560 bytes and the kernel often allocates them in
> times of extreme memory stress. We really really want them to be
> backed by order=0 pages.

Hello, Andrew.

Following patch would fix this problem.

Thanks.

-------------------8<------------------------
>From 7f21232d1eeffccdbd0f6d79c04d297cf95a713e Mon Sep 17 00:00:00 2001
From: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Date: Wed, 4 Dec 2013 10:36:11 +0900
Subject: [PATCH] slub: fix high order page allocation problem with
__GFP_NOFAIL

SLUB already try to allocate high order page with clearing __GFP_NOFAIL.
But, when allocating shadow page for kmemcheck, it missed clearing
the flag. This trigger WARN_ON_ONCE() reported by Christian Casteyde.

https://bugzilla.kernel.org/show_bug.cgi?id=65991

This patch fix this situation by using same allocation flag as original
allocation.

Reported-by: Christian Casteyde <casteyde.christian@free.fr>
Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>

diff --git a/mm/slub.c b/mm/slub.c
index 545a170..3dd28b1 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -1335,11 +1335,12 @@ static struct page *allocate_slab(struct kmem_cache *s, gfp_t flags, int node)
page = alloc_slab_page(alloc_gfp, node, oo);
if (unlikely(!page)) {
oo = s->min;
+ alloc_gfp = flags;
/*
* Allocation may have failed due to fragmentation.
* Try a lower order alloc if possible
*/
- page = alloc_slab_page(flags, node, oo);
+ page = alloc_slab_page(alloc_gfp, node, oo);

if (page)
stat(s, ORDER_FALLBACK);
@@ -1349,7 +1350,7 @@ static struct page *allocate_slab(struct kmem_cache *s, gfp_t flags, int node)
&& !(s->flags & (SLAB_NOTRACK | DEBUG_DEFAULT_FLAGS))) {
int pages = 1 << oo_order(oo);

- kmemcheck_alloc_shadow(page, oo_order(oo), flags, node);
+ kmemcheck_alloc_shadow(page, oo_order(oo), alloc_gfp, node);

/*
* Objects from caches that have a constructor don't get
--
1.7.9.5