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

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Message-Id: <20090421165022.F13F.A69D9226@jp.fujitsu.com>
Date:	Tue, 21 Apr 2009 18:03:25 +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

> 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) {
> 
> we need to ensure we don't recurse when PF_MEMALLOC is set.

It seems good idea.




> +static inline int
> +gfp_to_alloc_flags(gfp_t gfp_mask)
> +{
> +	struct task_struct *p = current;
> +	int alloc_flags = ALLOC_WMARK_MIN | ALLOC_CPUSET;
> +	const gfp_t wait = gfp_mask & __GFP_WAIT;
> +
> +	/*
> +	 * The caller may dip into page reserves a bit more if the caller
> +	 * cannot run direct reclaim, or if the caller has realtime scheduling
> +	 * policy or is asking for __GFP_HIGH memory.  GFP_ATOMIC requests will
> +	 * set both ALLOC_HARDER (!wait) and ALLOC_HIGH (__GFP_HIGH).
> +	 */
> +	if (gfp_mask & __GFP_HIGH)
> +		alloc_flags |= ALLOC_HIGH;
> +
> +	if (!wait) {
> +		alloc_flags |= ALLOC_HARDER;
> +		/*
> +		 * Ignore cpuset if GFP_ATOMIC (!wait) rather than fail alloc.
> +		 * See also cpuset_zone_allowed() comment in kernel/cpuset.c.
> +		 */
> +		alloc_flags &= ~ALLOC_CPUSET;
> +	} else if (unlikely(rt_task(p)) && !in_interrupt())

wait==1 and in_interrupt==1 is never occur.
I think in_interrupt check can be removed.


>  	/* Atomic allocations - we can't balance anything */
>  	if (!wait)
>  		goto nopage;
>  
> +	/* Avoid recursion of direct reclaim */
> +	if (p->flags & PF_MEMALLOC)
> +		goto nopage;
> +

Again. old code doesn't only check PF_MEMALLOC, but also check TIF_MEMDIE.


>  	/* Try direct reclaim and then allocating */
>  	page = __alloc_pages_direct_reclaim(gfp_mask, order,
>  					zonelist, high_zoneidx,
> -- 
> 1.5.6.5
> 



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