linux-kernel - Re: [PATCH] mm/vmscan.c: avoid recording the original scan targets in shrink

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Date:	Wed, 11 Jun 2014 11:21:37 +0800
From:	Chen Yucong <slaoub@...il.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	mgorman@...e.de, mhocko@...e.cz, hannes@...xchg.org,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/vmscan.c: avoid recording the original scan targets
 in shrink_lruvec()

On Tue, 2014-06-10 at 16:33 -0700, Andrew Morton wrote:
> >                       break;
> >  
> >               if (nr_file > nr_anon) {
> > -                     unsigned long scan_target =
> targets[LRU_INACTIVE_ANON] +
> >
> -                                             targets[LRU_ACTIVE_ANON]
> + 1;
> > +                     nr_to_scan = nr_file - ratio * nr_anon;
> > +                     percentage = nr[LRU_FILE] * 100 / nr_file;
> 
> here, nr_file and nr_anon are derived from the contents of nr[].  But
> nr[] was modified in the for_each_evictable_lru() loop, so its
> contents
> now may differ from what was in targets[]? 

nr_to_scan is used for recording the number of pages that should be
scanned to keep original *ratio*.

We can assume that the value of (nr_file > nr_anon) is true, nr_to_scan
should be distribute to nr[LRU_ACTIVE_FILE] and nr[LRU_INACTIVE_FILE] in
proportion.

    nr_file = nr[LRU_ACTIVE_FILE] + nr[LRU_INACTIVE_FILE];
    percentage = nr[LRU_FILE] / nr_file;

Note that in comparison with *old* percentage, the "new" percentage has
the different meaning. It is just used to divide nr_so_scan pages
appropriately.

thx!
cyc     

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