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

[Eric B Munson <emunson@akamai.com>]

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On Mon, 30 Mar 2015, Andrew Morton wrote:

> On Mon, 30 Mar 2015 14:31:14 -0400 Eric B Munson <emunson@akamai.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@There is a sysctl to control@/proc/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
> _
> 

That looks good, thanks.

Eric

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