linux-kernel - Re: [PATCH] mm, slaub: Add __GFP

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Date:	Fri, 10 Jun 2016 12:12:45 +0200
From:	Vlastimil Babka <vbabka@...e.cz>
To:	Mel Gorman <mgorman@...hsingularity.net>,
	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Marcin Wojtas <mw@...ihalf.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm, slaub: Add __GFP_ATOMIC to the GFP reclaim mask

On 06/10/2016 11:38 AM, Mel Gorman wrote:
> Commit d0164adc89f6 ("mm, page_alloc: distinguish between being unable to
> sleep, unwilling to sleep and avoiding waking kswapd") modified __GFP_WAIT
> to explicitly identify the difference between atomic callers and those that
> were unwilling to sleep. Later the definition was removed entirely.
> 
> The GFP_RECLAIM_MASK is the set of flags that affect watermark checking
> and reclaim behaviour but __GFP_ATOMIC was never added. Without it, atomic
> users of the slab allocator strip the __GFP_ATOMIC flag and cannot access
> the page allocator atomic reserves.  This patch addresses the problem.
> 
> The user-visible impact depends on the workload but potentially atomic
> allocations unnecessarily fail without this path.
> 
> Cc: <stable@...r.kernel.org> # 4.4+
> Reported-by: Marcin Wojtas <mw@...ihalf.com>
> Signed-off-by: Mel Gorman <mgorman@...hsingularity.net>

Acked-by: Vlastimil Babka <vbabka@...e.cz>

> ---
>  mm/internal.h | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/internal.h b/mm/internal.h
> index a37e5b6f9d25..2524ec880e24 100644
> --- a/mm/internal.h
> +++ b/mm/internal.h
> @@ -24,7 +24,8 @@
>   */
>  #define GFP_RECLAIM_MASK (__GFP_RECLAIM|__GFP_HIGH|__GFP_IO|__GFP_FS|\
>  			__GFP_NOWARN|__GFP_REPEAT|__GFP_NOFAIL|\
> -			__GFP_NORETRY|__GFP_MEMALLOC|__GFP_NOMEMALLOC)
> +			__GFP_NORETRY|__GFP_MEMALLOC|__GFP_NOMEMALLOC|\
> +			__GFP_ATOMIC)
>  
>  /* The GFP flags allowed during early boot */
>  #define GFP_BOOT_MASK (__GFP_BITS_MASK & ~(__GFP_RECLAIM|__GFP_IO|__GFP_FS))
>