Re: [PATCH RFC 1/4] mm: throttle MADV_FREE

[Michal Hocko <mhocko@suse.cz>]

On Tue 24-02-15 14:54:01, Shaohua Li wrote:
> On Tue, Feb 24, 2015 at 04:43:18PM +0100, Michal Hocko wrote:
> > On Tue 24-02-15 17:18:14, Minchan Kim wrote:
> > > Recently, Shaohua reported that MADV_FREE is much slower than
> > > MADV_DONTNEED in his MADV_FREE bomb test. The reason is many of
> > > applications went to stall with direct reclaim since kswapd's
> > > reclaim speed isn't fast than applications's allocation speed
> > > so that it causes lots of stall and lock contention.
> > 
> > I am not sure I understand this correctly. So the issue is that there is
> > huge number of MADV_FREE on the LRU and they are not close to the tail
> > of the list so the reclaim has to do a lot of work before it starts
> > dropping them?
> 
> I thought the main reason is current reclaim stragety. Anonymous pages are
> considered to be hard to be reclaimed with current policy, VM bias to reclaim
> file pages (anon pages are in active list first, referenced pte will reactivate
> anon pages and increase rotate count)

Makes sense. We are really biasing to page cache reclaim most of the
time.

-- 
Michal Hocko
SUSE Labs