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SubjectRe: [PATCH 1/2] mm, oom: make sure that the oom victim uses memory reserves
On Fri 19-05-17 21:12:36, Tetsuo Handa wrote:
> >From 41b663d0324bbaa29c01d7fee01e897b8b3b7397 Mon Sep 17 00:00:00 2001
> From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> Date: Fri, 19 May 2017 21:06:49 +0900
> Subject: [PATCH] mm,page_alloc: Make sure OOM victim can try allocations with
> no watermarks once
>
> Roman Gushchin has reported that the OOM killer can trivially selects next
> OOM victim when a thread doing memory allocation from page fault path was
> selected as first OOM victim.
>
> ----------
> [ 25.721494] allocate invoked oom-killer: gfp_mask=0x14280ca(GFP_HIGHUSER_MOVABLE|__GFP_ZERO), nodemask=(null), order=0, oom_score_adj=0
> [ 25.725658] allocate cpuset=/ mems_allowed=0
> [ 25.727033] CPU: 1 PID: 492 Comm: allocate Not tainted 4.12.0-rc1-mm1+ #181
> [ 25.729215] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Ubuntu-1.8.2-1ubuntu1 04/01/2014
> [ 25.729598] Call Trace:
> [ 25.729598] dump_stack+0x63/0x82
> [ 25.729598] dump_header+0x97/0x21a
> [ 25.729598] ? do_try_to_free_pages+0x2d7/0x360
> [ 25.729598] ? security_capable_noaudit+0x45/0x60
> [ 25.729598] oom_kill_process+0x219/0x3e0
> [ 25.729598] out_of_memory+0x11d/0x480
> [ 25.729598] __alloc_pages_slowpath+0xc84/0xd40
> [ 25.729598] __alloc_pages_nodemask+0x245/0x260
> [ 25.729598] alloc_pages_vma+0xa2/0x270
> [ 25.729598] __handle_mm_fault+0xca9/0x10c0
> [ 25.729598] handle_mm_fault+0xf3/0x210
> [ 25.729598] __do_page_fault+0x240/0x4e0
> [ 25.729598] trace_do_page_fault+0x37/0xe0
> [ 25.729598] do_async_page_fault+0x19/0x70
> [ 25.729598] async_page_fault+0x28/0x30
> (...snipped...)
> [ 25.781882] Out of memory: Kill process 492 (allocate) score 899 or sacrifice child
> [ 25.783874] Killed process 492 (allocate) total-vm:2052368kB, anon-rss:1894576kB, file-rss:4kB, shmem-rss:0kB
> [ 25.785680] allocate: page allocation failure: order:0, mode:0x14280ca(GFP_HIGHUSER_MOVABLE|__GFP_ZERO), nodemask=(null)
> [ 25.786797] allocate cpuset=/ mems_allowed=0
> [ 25.787246] CPU: 1 PID: 492 Comm: allocate Not tainted 4.12.0-rc1-mm1+ #181
> [ 25.787935] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Ubuntu-1.8.2-1ubuntu1 04/01/2014
> [ 25.788867] Call Trace:
> [ 25.789119] dump_stack+0x63/0x82
> [ 25.789451] warn_alloc+0x114/0x1b0
> [ 25.789451] __alloc_pages_slowpath+0xd32/0xd40
> [ 25.789451] __alloc_pages_nodemask+0x245/0x260
> [ 25.789451] alloc_pages_vma+0xa2/0x270
> [ 25.789451] __handle_mm_fault+0xca9/0x10c0
> [ 25.789451] handle_mm_fault+0xf3/0x210
> [ 25.789451] __do_page_fault+0x240/0x4e0
> [ 25.789451] trace_do_page_fault+0x37/0xe0
> [ 25.789451] do_async_page_fault+0x19/0x70
> [ 25.789451] async_page_fault+0x28/0x30
> (...snipped...)
> [ 25.810868] oom_reaper: reaped process 492 (allocate), now anon-rss:0kB, file-rss:0kB, shmem-rss:0kB
> (...snipped...)
> [ 25.817589] allocate invoked oom-killer: gfp_mask=0x0(), nodemask=(null), order=0, oom_score_adj=0
> [ 25.818821] allocate cpuset=/ mems_allowed=0
> [ 25.819259] CPU: 1 PID: 492 Comm: allocate Not tainted 4.12.0-rc1-mm1+ #181
> [ 25.819847] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Ubuntu-1.8.2-1ubuntu1 04/01/2014
> [ 25.820549] Call Trace:
> [ 25.820733] dump_stack+0x63/0x82
> [ 25.820961] dump_header+0x97/0x21a
> [ 25.820961] ? security_capable_noaudit+0x45/0x60
> [ 25.820961] oom_kill_process+0x219/0x3e0
> [ 25.820961] out_of_memory+0x11d/0x480
> [ 25.820961] pagefault_out_of_memory+0x68/0x80
> [ 25.820961] mm_fault_error+0x8f/0x190
> [ 25.820961] ? handle_mm_fault+0xf3/0x210
> [ 25.820961] __do_page_fault+0x4b2/0x4e0
> [ 25.820961] trace_do_page_fault+0x37/0xe0
> [ 25.820961] do_async_page_fault+0x19/0x70
> [ 25.820961] async_page_fault+0x28/0x30
> (...snipped...)
> [ 25.863078] Out of memory: Kill process 233 (firewalld) score 10 or sacrifice child
> [ 25.863634] Killed process 233 (firewalld) total-vm:246076kB, anon-rss:20956kB, file-rss:0kB, shmem-rss:0kB
> ----------
>
> There is a race window that the OOM reaper completes reclaiming the first
> victim's memory while nothing but mutex_trylock() prevents the first victim
> from calling out_of_memory() from pagefault_out_of_memory() after memory
> allocation for page fault path failed due to being selected as an OOM
> victim.
>
> This is a side effect of commit 9a67f6488eca926f ("mm: consolidate
> GFP_NOFAIL checks in the allocator slowpath") because that commit
> silently changed the behavior from
>
> /* Avoid allocations with no watermarks from looping endlessly */
>
> to
>
> /*
> * Give up allocations without trying memory reserves if selected
> * as an OOM victim
> */
>
> in __alloc_pages_slowpath() by moving the location to check TIF_MEMDIE
> flag. I have noticed this change but I didn't post a patch because
> I thought it is an acceptable change other than noise by warn_alloc()
> because !__GFP_NOFAIL allocations are allowed to fail.
> But we overlooked that failing memory allocation from page fault path
> makes difference due to the race window explained above.
>
> While it might be possible to add a check to pagefault_out_of_memory()
> that prevents the first victim from calling out_of_memory() or remove
> out_of_memory() from pagefault_out_of_memory(), changing
> pagefault_out_of_memory() does not suppress noise by warn_alloc() when
> allocating thread was selected as an OOM victim. There is little point
> with printing similar backtraces and memory information from both
> out_of_memory() and warn_alloc().
>
> Instead, if we guarantee that current thread can try allocations with
> no watermarks once when current thread looping inside
> __alloc_pages_slowpath() was selected as an OOM victim, we can follow
> "who can use memory reserves" rules and suppress noise by warn_alloc()
> and prevent memory allocations from page fault path from calling
> pagefault_out_of_memory().
>
> If we take the comment literally, this patch would do
>
> - if (test_thread_flag(TIF_MEMDIE))
> - goto nopage;
> + if (alloc_flags == ALLOC_NO_WATERMARKS || (gfp_mask & __GFP_NOMEMALLOC))
> + goto nopage;
>
> because gfp_pfmemalloc_allowed() returns false if __GFP_NOMEMALLOC is
> given. But if I recall correctly (I couldn't find the message), the
> condition is meant to apply to only OOM victims despite the comment.
> Therefore, this patch preserves TIF_MEMDIE check.
>
> Reported-by: Roman Gushchin <guro@fb.com>
> Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> Cc: Michal Hocko <mhocko@suse.com>
> Fixes: 9a67f6488eca926f ("mm: consolidate GFP_NOFAIL checks in the allocator slowpath")
> Cc: stable # v4.11

I cannot say I would love how this gets convoluted but let's go with
what you have here and think about a cleaner version later.

Acked-by: Michal Hocko <mhocko@suse.com>

Thanks!

> ---
> mm/page_alloc.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index f9e450c..b7a6f58 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -3870,7 +3870,9 @@ bool gfp_pfmemalloc_allowed(gfp_t gfp_mask)
> goto got_pg;
>
> /* Avoid allocations with no watermarks from looping endlessly */
> - if (test_thread_flag(TIF_MEMDIE))
> + if (test_thread_flag(TIF_MEMDIE) &&
> + (alloc_flags == ALLOC_NO_WATERMARKS ||
> + (gfp_mask & __GFP_NOMEMALLOC)))
> goto nopage;
>
> /* Retry as long as the OOM killer is making progress */
> --
> 1.8.3.1

--
Michal Hocko
SUSE Labs

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