linux-kernel - Re: [PATCH] Document interaction between compaction and the unevictable LRU

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Message-Id: <20150330150939.2e0bd53a3a16ada4cce8ec05@linux-foundation.org>
Date:	Mon, 30 Mar 2015 15:09:39 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Eric B Munson <emunson@...mai.com>
Cc:	Jonathan Corbet <corbet@....net>, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Document interaction between compaction and the
 unevictable LRU

On Mon, 30 Mar 2015 14:31:14 -0400 Eric B Munson <emunson@...mai.com> wrote:

> The memory compaction code uses the migration code to do most of the
> work in compaction.  However, the compaction code interacts with the
> unevictable LRU differently than migration code and this difference
> should be noted in the documentation.
> 
> --- a/Documentation/vm/unevictable-lru.txt
> +++ b/Documentation/vm/unevictable-lru.txt
> @@ -450,6 +451,16 @@ list because of a race between munlock and migration, page migration uses the
>  putback_lru_page() function to add migrated pages back to the LRU.
>  
>  
> +COMPACTING MLOCKED PAGES
> +------------------------
> +
> +The unevictable LRU can be scanned for compactable regions and the default
> +behavior is to do so.  There is a sysctl to control this behavior (see
> +Documentation/sysctl/vm.txt).  Once scanning of the unevictable LRU is
> +enabled, the work of compaction is mostly handled by the page migration code
> +and the same work flow as described in MIGRATING MLOCKED PAGES will apply.
> +

Thanks.  Let's tell people what this sysctl is called?


s@...re is a sysctl to control@...oc/sys/vm/compact_unevictable_allowed controls@:

--- a/Documentation/vm/unevictable-lru.txt~document-interaction-between-compaction-and-the-unevictable-lru-fix
+++ a/Documentation/vm/unevictable-lru.txt
@@ -455,10 +455,11 @@ COMPACTING MLOCKED PAGES
 ------------------------
 
 The unevictable LRU can be scanned for compactable regions and the default
-behavior is to do so.  There is a sysctl to control this behavior (see
-Documentation/sysctl/vm.txt).  Once scanning of the unevictable LRU is
-enabled, the work of compaction is mostly handled by the page migration code
-and the same work flow as described in MIGRATING MLOCKED PAGES will apply.
+behavior is to do so.  /proc/sys/vm/compact_unevictable_allowed controls
+this behavior (see Documentation/sysctl/vm.txt).  Once scanning of the
+unevictable LRU is enabled, the work of compaction is mostly handled by
+the page migration code and the same work flow as described in MIGRATING
+MLOCKED PAGES will apply.
 
 
 mmap(MAP_LOCKED) SYSTEM CALL HANDLING
_

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