linux-ext4 - Re: [PATCH 2/3] mm: slub: Do not take expensive steps for SLUBs speculative high-order allocations

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Date:	Wed, 11 May 2011 22:10:43 +0100
From:	Mel Gorman <mgorman@...e.de>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	James Bottomley <James.Bottomley@...senpartnership.com>,
	Colin King <colin.king@...onical.com>,
	Raghavendra D Prabhu <raghu.prabhu13@...il.com>,
	Jan Kara <jack@...e.cz>, Chris Mason <chris.mason@...cle.com>,
	Christoph Lameter <cl@...ux.com>,
	Pekka Enberg <penberg@...nel.org>,
	Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-ext4 <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH 2/3] mm: slub: Do not take expensive steps for SLUBs
 speculative high-order allocations

On Wed, May 11, 2011 at 01:38:44PM -0700, David Rientjes wrote:
> On Wed, 11 May 2011, Mel Gorman wrote:
> 
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index 9f8a97b..057f1e2 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -1972,6 +1972,7 @@ gfp_to_alloc_flags(gfp_t gfp_mask)
> >  {
> >  	int alloc_flags = ALLOC_WMARK_MIN | ALLOC_CPUSET;
> >  	const gfp_t wait = gfp_mask & __GFP_WAIT;
> > +	const gfp_t can_wake_kswapd = !(gfp_mask & __GFP_NO_KSWAPD);
> >  
> >  	/* __GFP_HIGH is assumed to be the same as ALLOC_HIGH to save a branch. */
> >  	BUILD_BUG_ON(__GFP_HIGH != (__force gfp_t) ALLOC_HIGH);
> > @@ -1984,7 +1985,7 @@ gfp_to_alloc_flags(gfp_t gfp_mask)
> >  	 */
> >  	alloc_flags |= (__force int) (gfp_mask & __GFP_HIGH);
> >  
> > -	if (!wait) {
> > +	if (!wait && can_wake_kswapd) {
> >  		/*
> >  		 * Not worth trying to allocate harder for
> >  		 * __GFP_NOMEMALLOC even if it can't schedule.
> > diff --git a/mm/slub.c b/mm/slub.c
> > index 98c358d..1071723 100644
> > --- a/mm/slub.c
> > +++ b/mm/slub.c
> > @@ -1170,7 +1170,8 @@ static struct page *allocate_slab(struct kmem_cache *s, gfp_t flags, int node)
> >  	 * Let the initial higher-order allocation fail under memory pressure
> >  	 * so we fall-back to the minimum order allocation.
> >  	 */
> > -	alloc_gfp = (flags | __GFP_NOWARN | __GFP_NORETRY | __GFP_NO_KSWAPD) & ~__GFP_NOFAIL;
> > +	alloc_gfp = (flags | __GFP_NOWARN | __GFP_NORETRY | __GFP_NO_KSWAPD) &
> > +			~(__GFP_NOFAIL | __GFP_WAIT);
> 
> __GFP_NORETRY is a no-op without __GFP_WAIT.
> 

True. I'll remove it in a V2 but I won't respin just yet.

> >  
> >  	page = alloc_slab_page(alloc_gfp, node, oo);
> >  	if (unlikely(!page)) {

-- 
Mel Gorman
SUSE Labs
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