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SubjectRe: System freezes after OOM
On Wed, 13 Jul 2016, Tetsuo Handa wrote:

> I wonder whether commit f9054c70d28bc214 ("mm, mempool: only set
> __GFP_NOMEMALLOC if there are free elements") is doing correct thing.
> It says
>
> If an oom killed thread calls mempool_alloc(), it is possible that it'll
> loop forever if there are no elements on the freelist since
> __GFP_NOMEMALLOC prevents it from accessing needed memory reserves in
> oom conditions.
>
> but we can allow mempool_alloc(__GFP_NOMEMALLOC) requests to access
> memory reserves via below change, can't we? The purpose of allowing
> ALLOC_NO_WATERMARKS via TIF_MEMDIE is to make sure current allocation
> request does not to loop forever inside the page allocator, isn't it?

This would defeat the purpose of __GFP_NOMEMALLOC for oom killed threads,
so you'd need to demonstrate that isn't a problem for the current users
and then change the semantics of the gfp flag.

> Why we need to allow mempool_alloc(__GFP_NOMEMALLOC) requests to use
> ALLOC_NO_WATERMARKS when TIF_MEMDIE is not set?
>

mempool_alloc(__GFP_NOMEMALLOC) is forbidden.

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