linux-kernel - Re: [merged] mm-page_alloc-reset-aging-cycle-with-gfp

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Date:	Thu, 6 Mar 2014 15:12:06 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Johannes Weiner <hannes@...xchg.org>
Cc:	stable@...nel.org, riel@...hat.com, mgorman@...e.de,
	jstancek@...hat.com, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [merged]
 mm-page_alloc-reset-aging-cycle-with-gfp_thisnode-v2.patch removed from -mm
 tree

On Thu, 6 Mar 2014 18:04:04 -0500 Johannes Weiner <hannes@...xchg.org> wrote:

> > what bug does it fix and what are the user-visible effects??
> 
> Ok, maybe this is better?
> 
> ---
> 
> GFP_THISNODE is for callers that implement their own clever fallback
> to remote nodes.  It restricts the allocation to the specified node
> and does not invoke reclaim, assuming that the caller will take care
> of it when the fallback fails, e.g. through a subsequent allocation
> request without GFP_THISNODE set.
> 
> However, many current GFP_THISNODE users only want the node exclusive
> aspect of the flag, without actually implementing their own fallback
> or triggering reclaim if necessary.  This results in things like page
> migration failing prematurely even when there is easily reclaimable
> memory available, unless kswapd happens to be running already or a
> concurrent allocation attempt triggers the necessary reclaim.
> 
> Convert all callsites that don't implement their own fallback strategy
> to __GFP_THISNODE.  This restricts the allocation a single node too,
> but at the same time allows the allocator to enter the slowpath, wake
> kswapd, and invoke direct reclaim if necessary, to make the allocation
> happen when memory is full.

Looks good, thanks.  I'll send this Linuswards next week.
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