From: David Rientjes <rientjes@google.com>
To: Vlastimil Babka <vbabka@suse.cz>
Cc: Andrew Morton <akpm@linux-foundation.org>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
Michal Hocko <mhocko@kernel.org>,
Mel Gorman <mgorman@techsingularity.net>,
Joonsoo Kim <iamjoonsoo.kim@lge.com>,
Rik van Riel <riel@redhat.com>
Subject: Re: [PATCH 5/8] mm, page_alloc: make THP-specific decisions more generic
Date: Tue, 19 Jul 2016 16:10:31 -0700 (PDT) [thread overview]
Message-ID: <alpine.DEB.2.10.1607191608550.19940@chino.kir.corp.google.com> (raw)
In-Reply-To: <20160718112302.27381-6-vbabka@suse.cz>
On Mon, 18 Jul 2016, Vlastimil Babka wrote:
> Since THP allocations during page faults can be costly, extra decisions are
> employed for them to avoid excessive reclaim and compaction, if the initial
> compaction doesn't look promising. The detection has never been perfect as
> there is no gfp flag specific to THP allocations. At this moment it checks the
> whole combination of flags that makes up GFP_TRANSHUGE, and hopes that no other
> users of such combination exist, or would mind being treated the same way.
> Extra care is also taken to separate allocations from khugepaged, where latency
> doesn't matter that much.
>
> It is however possible to distinguish these allocations in a simpler and more
> reliable way. The key observation is that after the initial compaction followed
> by the first iteration of "standard" reclaim/compaction, both __GFP_NORETRY
> allocations and costly allocations without __GFP_REPEAT are declared as
> failures:
>
> /* Do not loop if specifically requested */
> if (gfp_mask & __GFP_NORETRY)
> goto nopage;
>
> /*
> * Do not retry costly high order allocations unless they are
> * __GFP_REPEAT
> */
> if (order > PAGE_ALLOC_COSTLY_ORDER && !(gfp_mask & __GFP_REPEAT))
> goto nopage;
>
> This means we can further distinguish allocations that are costly order *and*
> additionally include the __GFP_NORETRY flag. As it happens, GFP_TRANSHUGE
> allocations do already fall into this category. This will also allow other
> costly allocations with similar high-order benefit vs latency considerations to
> use this semantic. Furthermore, we can distinguish THP allocations that should
> try a bit harder (such as from khugepageed) by removing __GFP_NORETRY, as will
> be done in the next patch.
>
> Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
> Acked-by: Michal Hocko <mhocko@suse.com>
I think this is fine, but I would hope that we could check
gfp_pfmemalloc_allowed() before compacting and failing even for costly
orders when otherwise the first get_page_from_freelist() in the slowpath
may have succeeded due to watermarks.
next prev parent reply other threads:[~2016-07-19 23:10 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-07-18 11:22 [PATCH 0/8] compaction-related cleanups v4 Vlastimil Babka
2016-07-18 11:22 ` [PATCH 1/8] mm, compaction: don't isolate PageWriteback pages in MIGRATE_SYNC_LIGHT mode Vlastimil Babka
2016-07-19 22:21 ` David Rientjes
2016-07-18 11:22 ` [PATCH 2/8] mm, page_alloc: set alloc_flags only once in slowpath Vlastimil Babka
2016-07-18 11:27 ` Michal Hocko
2016-07-19 22:28 ` David Rientjes
2016-07-21 7:00 ` Vlastimil Babka
2016-07-18 11:22 ` [PATCH 3/8] mm, page_alloc: don't retry initial attempt " Vlastimil Babka
2016-07-18 11:29 ` Michal Hocko
2016-07-18 11:34 ` Vlastimil Babka
2016-07-19 22:36 ` David Rientjes
2016-07-20 15:25 ` Vlastimil Babka
2016-07-20 22:00 ` David Rientjes
2016-07-18 11:22 ` [PATCH 4/8] mm, page_alloc: restructure direct compaction handling " Vlastimil Babka
2016-07-19 22:50 ` David Rientjes
2016-07-20 16:02 ` Vlastimil Babka
2016-07-18 11:22 ` [PATCH 5/8] mm, page_alloc: make THP-specific decisions more generic Vlastimil Babka
2016-07-19 23:10 ` David Rientjes [this message]
2016-07-21 7:13 ` Vlastimil Babka
2016-07-18 11:23 ` [PATCH 6/8] mm, thp: remove __GFP_NORETRY from khugepaged and madvised allocations Vlastimil Babka
2016-07-18 11:23 ` [PATCH 7/8] mm, compaction: introduce direct compaction priority Vlastimil Babka
2016-07-18 11:23 ` [PATCH 8/8] mm, compaction: simplify contended compaction handling Vlastimil Babka
2016-07-18 11:30 ` [PATCH 0/8] compaction-related cleanups v4 Michal Hocko
2016-07-18 15:41 ` Mel Gorman
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