From: Mel Gorman <mgorman@suse.de>
To: Michal Hocko <mhocko@kernel.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>,
Hillf Danton <hdanton@sina.com>, Vlastimil Babka <vbabka@suse.cz>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
linux-kernel <linux-kernel@vger.kernel.org>,
Johannes Weiner <hannes@cmpxchg.org>
Subject: Re: [Question] Should direct reclaim time be bounded?
Date: Fri, 12 Jul 2019 10:49:19 +0100 [thread overview]
Message-ID: <20190712094919.GI13484@suse.de> (raw)
In-Reply-To: <20190711071245.GB29483@dhcp22.suse.cz>
On Thu, Jul 11, 2019 at 09:12:45AM +0200, Michal Hocko wrote:
> On Wed 10-07-19 16:36:58, Mike Kravetz wrote:
> > On 7/10/19 12:44 PM, Michal Hocko wrote:
> > > On Wed 10-07-19 11:42:40, Mike Kravetz wrote:
> > > [...]
> > >> As Michal suggested, I'm going to do some testing to see what impact
> > >> dropping the __GFP_RETRY_MAYFAIL flag for these huge page allocations
> > >> will have on the number of pages allocated.
> > >
> > > Just to clarify. I didn't mean to drop __GFP_RETRY_MAYFAIL from the
> > > allocation request. I meant to drop the special casing of the flag in
> > > should_continue_reclaim. I really have hard time to argue for this
> > > special casing TBH. The flag is meant to retry harder but that shouldn't
> > > be reduced to a single reclaim attempt because that alone doesn't really
> > > help much with the high order allocation. It is more about compaction to
> > > be retried harder.
> >
> > Thanks Michal. That is indeed what you suggested earlier. I remembered
> > incorrectly. Sorry.
> >
> > Removing the special casing for __GFP_RETRY_MAYFAIL in should_continue_reclaim
> > implies that it will return false if nothing was reclaimed (nr_reclaimed == 0)
> > in the previous pass.
> >
> > When I make such a modification and test, I see long stalls as a result
> > of should_compact_retry returning true too often. On a system I am currently
> > testing, should_compact_retry has returned true 36000000 times. My guess
> > is that this may stall forever. Vlastmil previously asked about this behavior,
> > so I am capturing the reason. Like before [1], should_compact_retry is
> > returning true mostly because compaction_withdrawn() returns COMPACT_DEFERRED.
>
> This smells like a problem to me. But somebody more familiar with
> compaction should comment.
>
Examine in should_compact_retry if it's retrying because
compaction_zonelist_suitable is true. Looking at it now, it would not
necessarily do the right thing because any non-skipped zone would make
it eligible which is too strong a condition as COMPACT_SKIPPED is not
reliably set. If that function is the case, it would be reasonable
remove "ret = compaction_zonelist_suitable(ac, order, alloc_flags);" and
the implementation of compaction_zonelist_suitable entirely as part of
your fix.
--
Mel Gorman
SUSE Labs
next prev parent reply other threads:[~2019-07-12 9:49 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-04-23 4:07 [Question] Should direct reclaim time be bounded? Mike Kravetz
2019-04-23 7:19 ` Michal Hocko
2019-04-23 16:39 ` Mike Kravetz
2019-04-24 14:35 ` Vlastimil Babka
2019-06-28 18:20 ` Mike Kravetz
2019-07-01 8:59 ` Mel Gorman
2019-07-02 3:15 ` Mike Kravetz
2019-07-03 9:43 ` Mel Gorman
2019-07-03 23:54 ` Mike Kravetz
2019-07-04 11:09 ` Michal Hocko
2019-07-04 15:11 ` Mike Kravetz
2019-07-10 18:42 ` Mike Kravetz
2019-07-10 19:44 ` Michal Hocko
2019-07-10 23:36 ` Mike Kravetz
2019-07-11 7:12 ` Michal Hocko
2019-07-12 9:49 ` Mel Gorman [this message]
[not found] <20190712054732.7264-1-hdanton@sina.com>
2019-07-13 1:11 ` Mike Kravetz
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