Re: [patch 1/8] mm: memcg: only evict file pages when we have plenty

[Simon Jeons]

On 12/13/2012 10:55 PM, Michal Hocko wrote:
> On Wed 12-12-12 17:28:44, Johannes Weiner wrote:
> > On Wed, Dec 12, 2012 at 04:53:36PM -0500, Rik van Riel wrote:
> > > On 12/12/2012 04:43 PM, Johannes Weiner wrote:
> > > > dc0422c "mm: vmscan: only evict file pages when we have plenty" makes
> > > > a point of not going for anonymous memory while there is still enough
> > > > inactive cache around.
> > > >
> > > > The check was added only for global reclaim, but it is just as useful
> > > > for memory cgroup reclaim.
> > > >
> > > > Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>
> > > > ---
> > > >   mm/vmscan.c | 19 ++++++++++---------
> > > >   1 file changed, 10 insertions(+), 9 deletions(-)
> > > >
> > > > diff --git a/mm/vmscan.c b/mm/vmscan.c
> > > > index 157bb11..3874dcb 100644
> > > > --- a/mm/vmscan.c
> > > > +++ b/mm/vmscan.c
> > > > @@ -1671,6 +1671,16 @@ static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
> > > >   		denominator = 1;
> > > >   		goto out;
> > > >   	}
> > > > +	/*
> > > > +	 * There is enough inactive page cache, do not reclaim
> > > > +	 * anything from the anonymous working set right now.
> > > > +	 */
> > > > +	if (!inactive_file_is_low(lruvec)) {
> > > > +		fraction[0] = 0;
> > > > +		fraction[1] = 1;
> > > > +		denominator = 1;
> > > > +		goto out;
> > > > +	}
> > > >
> > > >   	anon  = get_lru_size(lruvec, LRU_ACTIVE_ANON) +
> > > >   		get_lru_size(lruvec, LRU_INACTIVE_ANON);
> > > > @@ -1688,15 +1698,6 @@ static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
> > > >   			fraction[1] = 0;
> > > >   			denominator = 1;
> > > >   			goto out;
> > > > -		} else if (!inactive_file_is_low_global(zone)) {
> > > > -			/*
> > > > -			 * There is enough inactive page cache, do not
> > > > -			 * reclaim anything from the working set right now.
> > > > -			 */
> > > > -			fraction[0] = 0;
> > > > -			fraction[1] = 1;
> > > > -			denominator = 1;
> > > > -			goto out;
> > > >   		}
> > > >   	}
> > > I believe the if() block should be moved to AFTER
> > > the check where we make sure we actually have enough
> > > file pages.
> > You are absolutely right, this makes more sense.  Although I'd figure
> > the impact would be small because if there actually is that little
> > file cache, it won't be there for long with force-file scanning... :-)
> Yes, I think that the result would be worse (more swapping) so the
> change can only help.
>
> > I moved the condition, but it throws conflicts in the rest of the
> > series.  Will re-run tests, wait for Michal and Mel, then resend.
> Yes the patch makes sense for memcg as well. I guess you have tested
> this primarily with memcg. Do you have any numbers? Would be nice to put
> them into the changelog if you have (it should help to reduce swapping
> with heavy streaming IO load).
>
> Acked-by: Michal Hocko <mhocko@xxxxxxx>

Hi Michal,

I still can't understand why "The goto out means that it should be fine 
either way.", could you explain to me, sorry for my stupid. :-)


Regards,
Simon



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