On Wed 08-11-17 20:01:46, Tetsuo Handa wrote:
> Manish Jaggi noticed that running LTP oom01/oom02 ltp tests with high core
> count causes random kernel panics when an OOM victim which consumed memory
> in a way the OOM reaper does not help was selected by the OOM killer [1].
> Since commit 696453e66630ad45 ("mm, oom: task_will_free_mem should skip
> oom_reaped tasks") changed task_will_free_mem(current) in out_of_memory()
> to return false as soon as MMF_OOM_SKIP is set, many threads sharing the
> victim's mm were not able to try allocation from memory reserves after the
> OOM reaper gave up reclaiming memory.
>
> Therefore, this patch allows OOM victims to use ALLOC_OOM watermark for
> last second allocation attempt.
>
> [1] http://lkml.kernel.org/r/e6c83a26-1d59-4afd-55cf-04e58bdde188@xxxxxxxxxxxxxxxxxx
>
> Fixes: 696453e66630ad45 ("mm, oom: task_will_free_mem should skip oom_reaped tasks")
> Reported-by: Manish Jaggi <mjaggi@xxxxxxxxxxxxxxxxxx>
> Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxxx>
> Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
> Cc: Vladimir Davydov <vdavydov.dev@xxxxxxxxx>
> Cc: David Rientjes <rientjes@xxxxxxxxxx>
I do not like the changelog because it doesn't explain the race window
but the patch itself is OK. I have offered a better explanation [1] but
I will not really insist on my wording.
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
[1] http://lkml.kernel.org/r/20171101135855.bqg2kuj6ao2cicqi@xxxxxxxxxxxxxx
> ---
> mm/page_alloc.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 764f24c..fbbc95a 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -4153,13 +4153,19 @@ struct page *alloc_pages_before_oomkill(const struct oom_control *oc)
> * !__GFP_NORETRY allocation which will never fail due to oom_lock
> * already held. And since this allocation attempt does not sleep,
> * there is no reason we must use high watermark here.
> + * But anyway, make sure that OOM victims can try ALLOC_OOM watermark
> + * in case they haven't tried ALLOC_OOM watermark.
> */
> int alloc_flags = ALLOC_CPUSET | ALLOC_WMARK_HIGH;
> gfp_t gfp_mask = oc->gfp_mask | __GFP_HARDWALL;
> + int reserve_flags;
>
> if (!oc->ac)
> return NULL;
> gfp_mask &= ~__GFP_DIRECT_RECLAIM;
> + reserve_flags = __gfp_pfmemalloc_flags(gfp_mask);
> + if (reserve_flags)
> + alloc_flags = reserve_flags;
> return get_page_from_freelist(gfp_mask, oc->order, alloc_flags, oc->ac);
> }
>
> --
> 1.8.3.1
>
--
Michal Hocko
SUSE Labs
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