Re: Problem in Page Cache Replacement

[Jaegeuk Hanse]

On 11/22/2012 11:53 PM, Fengguang Wu wrote:
> On Thu, Nov 22, 2012 at 11:41:07PM +0800, Fengguang Wu wrote:
> > On Wed, Nov 21, 2012 at 12:07:22PM +0200, Metin DÃÅlà wrote:
> > > On Wed, Nov 21, 2012 at 12:00 PM, Jaegeuk Hanse <jaegeuk.hanse@xxxxxxxxx> wrote:
> > > > On 11/21/2012 05:58 PM, metin d wrote:
> > > >
> > > > Hi Fengguang,
> > > >
> > > > I run tests and attached the results. The line below I guess shows the data-1 page caches.
> > > >
> > > > 0x000000080000006c       6584051    25718  __RU_lA___________________P________    referenced,uptodate,lru,active,private
> > > >
> > > >
> > > > I thinks this is just one state of page cache pages.
> > > But why these page caches are in this state as opposed to other page
> > > caches. From the results I conclude that:
> > >
> > > data-1 pages are in state : referenced,uptodate,lru,active,private
> > I wonder if it's this code that stops data-1 pages from being
> > reclaimed:
> >
> > shrink_page_list():
> >
> >                  if (page_has_private(page)) {
> >                          if (!try_to_release_page(page, sc->gfp_mask))
> >                                  goto activate_locked;
> >
> > What's the filesystem used?
> Ah it's more likely caused by this logic:
>
>          if (is_active_lru(lru)) {
>                  if (inactive_list_is_low(mz, file))
>                          shrink_active_list(nr_to_scan, mz, sc, priority, file);
>
> The active file list won't be scanned at all if it's smaller than the
> active list. In this case, it's inactive=33586MB > active=25719MB. So
> the data-1 pages in the active list will never be scanned and reclaimed.

Hi Fengguang,

It seems that most of data-1 file pages are in active lru cache and most 
of data-2 file pages are in inactive lru cache. As Johannes mentioned, 
if inter-reference distance is bigger than half of memory, the pages 
will not be actived. How you intend to resolve this issue? Is Johannes's 
inactive list threshing idea  available?

Regards,
Jaegeuk

> > > data-2 pages are in state : referenced,uptodate,lru,mappedtodisk
> > Thanks,
> > Fengguang

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