Re: [PATCH 1/3] mm, reclaim: make should_continue_reclaim performdryrun detection

[Hillf Danton <hdanton@sina.com>]

On Mon, 5 Aug 2019 16:43:04 +0800 Vlastimil Babka wrote:
> 
> On 8/3/19 12:39 AM, Mike Kravetz wrote:
> > From: Hillf Danton <hdanton@sina.com>
> >
> > Address the issue of should_continue_reclaim continuing true too often
> > for __GFP_RETRY_MAYFAIL attempts when !nr_reclaimed and nr_scanned.
> > This could happen during hugetlb page allocation causing stalls for
> > minutes or hours.
> >
> > We can stop reclaiming pages if compaction reports it can make a progress.
> > A code reshuffle is needed to do that.
> 
> > And it has side-effects, however,
> > with allocation latencies in other cases but that would come at the cost
> > of potential premature reclaim which has consequences of itself.
> 
> Based on Mel's longer explanation, can we clarify the wording here? e.g.:
> 
> There might be side-effect for other high-order allocations that would
> potentially benefit from more reclaim before compaction for them to be
> faster and less likely to stall, but the consequences of
> premature/over-reclaim are considered worse.
> 
> > We can also bail out of reclaiming pages if we know that there are not
> > enough inactive lru pages left to satisfy the costly allocation.
> >
> > We can give up reclaiming pages too if we see dryrun occur, with the
> > certainty of plenty of inactive pages. IOW with dryrun detected, we are
> > sure we have reclaimed as many pages as we could.
> >
> > Cc: Mike Kravetz <mike.kravetz@oracle.com>
> > Cc: Mel Gorman <mgorman@suse.de>
> > Cc: Michal Hocko <mhocko@kernel.org>
> > Cc: Vlastimil Babka <vbabka@suse.cz>
> > Cc: Johannes Weiner <hannes@cmpxchg.org>
> > Signed-off-by: Hillf Danton <hdanton@sina.com>
> > Tested-by: Mike Kravetz <mike.kravetz@oracle.com>
> > Acked-by: Mel Gorman <mgorman@suse.de>
> 
> Acked-by: Vlastimil Babka <vbabka@suse.cz>
> I will send some followup cleanup.
> 
> There should be also Mike's SOB?

Yes, definitely.

Thanks
Hillf