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From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
To: Mel Gorman <mel@csn.ul.ie>
Subject: Re: [PATCH 10/25] Calculate the alloc_flags for allocation only once
Cc: kosaki.motohiro@jp.fujitsu.com,
       Linux Memory Management List <linux-mm@kvack.org>,
       Christoph Lameter <cl@linux-foundation.org>,
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       Andrew Morton <akpm@linux-foundation.org>
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> The changelog now reads
> =====
> 
> Factor out the mapping between GFP and alloc_flags only once. Once factored
> out, it only needs to be calculated once but some care must be taken.
> 
> [neilb@suse.de says]
> As the test:
> 
> -       if (((p->flags & PF_MEMALLOC) ||
>         unlikely(test_thread_flag(TIF_MEMDIE)))
> -                       && !in_interrupt()) {
> -               if (!(gfp_mask & __GFP_NOMEMALLOC)) {
> 
> has been replaced with a slightly weaker one:
> 
> +       if (alloc_flags & ALLOC_NO_WATERMARKS) {
> 
> Without care, this would allow recursion into the allocator via direct
> reclaim. This patch ensures we do not recurse when PF_MEMALLOC is set
> but TF_MEMDIE callers are now allowed to directly reclaim where they
> would have been prevented in the past.

Excellent. :)