On Thu 17-11-16 21:50:04, Tetsuo Handa wrote:
> Filesystem code might request costly __GFP_NOFAIL !__GFP_REPEAT GFP_NOFS
> allocations. But commit 0a0337e0d1d13446 ("mm, oom: rework oom detection")
> overlooked that __GFP_NOFAIL allocation requests need to invoke the OOM
> killer and retry even if order > PAGE_ALLOC_COSTLY_ORDER && !__GFP_REPEAT.
> The caller will crash if such allocation request failed.
Could you point to such an allocation request please? Costly GFP_NOFAIL
requests are a really high requirement and I am even not sure we should
support them. buffered_rmqueue already warns about order > 1 NOFAIL
allocations.
I am not saying the patch is incorrect but it sounds more a theoretical
than practical issue which should be considered when involving the
stable tree here. To be honest I would rather see a single place which
handles all NOFAIL fallbacks rather than make the code even more
convoluted than it is already.
> Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxxx>
> Cc: <stable@xxxxxxxxxxxxxxx> # 4.7+
> ---
> mm/page_alloc.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 6de9440..b458f00 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -3650,9 +3650,10 @@ bool gfp_pfmemalloc_allowed(gfp_t gfp_mask)
>
> /*
> * Do not retry costly high order allocations unless they are
> - * __GFP_REPEAT
> + * __GFP_REPEAT or __GFP_NOFAIL
> */
> - if (order > PAGE_ALLOC_COSTLY_ORDER && !(gfp_mask & __GFP_REPEAT))
> + if (order > PAGE_ALLOC_COSTLY_ORDER &&
> + !(gfp_mask & (__GFP_REPEAT | __GFP_NOFAIL)))
> goto nopage;
>
> /* Make sure we know about allocations which stall for too long */
> --
> 1.8.3.1
>
--
Michal Hocko
SUSE Labs
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