linux-kernel - Re: [PATCH 10/25] Calculate the alloc

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Message-Id: <20090421193942.F171.A69D9226@jp.fujitsu.com>
Date:	Tue, 21 Apr 2009 19:40:14 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Mel Gorman <mel@....ul.ie>
Cc:	kosaki.motohiro@...fujitsu.com,
	Linux Memory Management List <linux-mm@...ck.org>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Nick Piggin <npiggin@...e.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Lin Ming <ming.m.lin@...el.com>,
	Zhang Yanmin <yanmin_zhang@...ux.intel.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 10/25] Calculate the alloc_flags for allocation only once

> 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@...e.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. :)



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