Re: [PATCH]mm:Correctly update number of rotated pages on active list.

["Pradeep Goswami (Pradeep Kumar Goswami)" <Pradeep.Goswami@spreadtrum.com>]

On Thu, Dec 03, 2015 at 11:59:48AM +0100, Michal Hocko wrote:
> On Thu 03-12-15 10:08:11, Pradeep Goswami (Pradeep Kumar Goswami) wrote:
> > This patch corrects the number of pages which are rotated on active list.
> > The counter for rotated pages effects the number of pages
> > to be scanned on active pages list in  low memory situations.
> 
> Why this should be changed?
> 
> This seems to be deliberate:
>         /*
>          * Count referenced pages from currently used mappings as rotated,
>          * even though only some of them are actually re-activated.  This
>          * helps balance scan pressure between file and anonymous pages in
>          * get_scan_count.
>          */
>         reclaim_stat->recent_rotated[file] += nr_rotated;
> 
> What kind of problem are you trying to fix?
Actually the numeber of pages which are actually rotated are wrongly
updated, So I thought this might be minor coding error but as pointed
out above, this seems to be deliberate. Thanks for clarifying.
> 
> > 
> > Signed-off-by: Pradeep Goswami <pradeep.goswami@spredtrum.com>
> > Cc: Rebecca Schultz Zavin <rebecca@android.com>
> > Cc: Vladimir Davydov <vdavydov@parallels.com>
> > Cc: Andrew Morton <akpm@linux-foundation.org>
> > ---
> > --- a/mm/vmscan.c       2015-11-18 20:55:38.208838142 +0800
> > +++ b/mm/vmscan.c       2015-11-19 14:37:31.189838998 +0800
> > @@ -1806,7 +1806,6 @@ static void shrink_active_list(unsigned
> >  
> >                 if (page_referenced(page, 0, sc->target_mem_cgroup,
> >                                     &vm_flags)) {
> > -                       nr_rotated += hpage_nr_pages(page);
> >                         /*  
> >                          * Identify referenced, file-backed active pages and 
> >                          * give them one more trip around the active list. So
> > @@ -1818,6 +1817,7 @@ static void shrink_active_list(unsigned
> >                          */  
> >                         if ((vm_flags & VM_EXEC) && page_is_file_cache(page)) {
> >                                 list_add(&page->lru, &l_active);
> > +                               nr_rotated += hpage_nr_pages(page);
> >                                 continue;
> >                         }   
> >                 }   
> > 
> > Thanks,
> > Pradeep.
> > --
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> 
> -- 
> Michal Hocko
> SUSE Labs
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