From: Michal Hocko <mhocko@suse.com>
To: Pavel Tatashin <pasha.tatashin@soleen.com>
Cc: LKML <linux-kernel@vger.kernel.org>,
linux-mm <linux-mm@kvack.org>,
Andrew Morton <akpm@linux-foundation.org>,
Vlastimil Babka <vbabka@suse.cz>,
David Hildenbrand <david@redhat.com>,
Oscar Salvador <osalvador@suse.de>,
Dan Williams <dan.j.williams@intel.com>,
Sasha Levin <sashal@kernel.org>,
Tyler Hicks <tyhicks@linux.microsoft.com>,
Joonsoo Kim <iamjoonsoo.kim@lge.com>,
mike.kravetz@oracle.com, Steven Rostedt <rostedt@goodmis.org>,
Ingo Molnar <mingo@redhat.com>, Jason Gunthorpe <jgg@ziepe.ca>,
Peter Zijlstra <peterz@infradead.org>,
Mel Gorman <mgorman@suse.de>,
Matthew Wilcox <willy@infradead.org>,
David Rientjes <rientjes@google.com>,
John Hubbard <jhubbard@nvidia.com>,
Linux Doc Mailing List <linux-doc@vger.kernel.org>
Subject: Re: [PATCH v3 3/6] mm: apply per-task gfp constraints in fast path
Date: Tue, 15 Dec 2020 09:25:24 +0100 [thread overview]
Message-ID: <20201215082524.GK32193@dhcp22.suse.cz> (raw)
In-Reply-To: <CA+CK2bA9u_ZUosha0JvW6ezs-h95UBHZztoFojMyFbC791ximw@mail.gmail.com>
On Tue 15-12-20 00:20:39, Pavel Tatashin wrote:
> > Ack to this.
>
> Thank you.
>
> >
> > But I do not really understand this. All allocation contexts should have
> > a proper gfp mask so why do we have to call current_gfp_context here?
> > In fact moving the current_gfp_context in the allocator path should have
> > made all this games unnecessary. Memcg reclaim path might need some
> > careful check because gfp mask is used more creative there but the
> > general reclaim paths should be ok.
> >
> > > diff --git a/mm/vmscan.c b/mm/vmscan.c
> >
> > Again, why do we need this when the gfp_mask
> > > };
> > >
> --
>
> Hi Michal,
>
> Beside from __alloc_pages_nodemask(), the current_gfp_context() is
> called from the following six functions:
>
> try_to_free_pages()
> try_to_free_mem_cgroup_pages()
> __node_reclaim()
> __need_fs_reclaim()
> alloc_contig_range()
> pcpu_alloc()
>
> As I understand, the idea is that because the allocator now honors
> gfp_context values for all paths, the call can be removed from some of
> the above functions. I think you are correct. But, at least from a
> quick glance, this is not obvious, and is not the case for all of the
> above functions.
>
> For example:
>
> alloc_contig_range()
> __alloc_contig_migrate_range
> isolate_migratepages_range
> isolate_migratepages_block
> /*
> * Only allow to migrate anonymous pages in GFP_NOFS context
> * because those do not depend on fs locks.
> */
> if (!(cc->gfp_mask & __GFP_FS) && page_mapping(page))
> goto isolate_fail;
>
> If we remove current_gfp_context() from alloc_contig_range(), the
> cc->gfp_mask will not be updated with proper __GFP_FS flag.
I do not think I was proposing to drop current_gfp_context from
alloc_contig_range. ACR needs some work to be properly scoped gfp mask
aware. This should be addressed but I do not think think the code
works properly now so I wouldn't lose sleep over it in this series. At
least __alloc_contig_migrate_range should follow the gfp mask given to
alloc_contig_range.
> I have studied some other paths, and they are also convoluted.
> Therefore, I am worried about performing this optimization in this
> series.
Dropping current_gfp_context from the reclaim context should be done in
a separate patch. I didn't mean to push for this here. All I meant was
to simply not touch gfp/zone_idx in the reclaim path. The changelog
should call out that the page allocator always provides proper gfp mask.
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2020-12-15 8:26 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-11 20:21 [PATCH v3 0/6] prohibit pinning pages in ZONE_MOVABLE Pavel Tatashin
2020-12-11 20:21 ` [PATCH v3 1/6] mm/gup: don't pin migrated cma pages in movable zone Pavel Tatashin
2020-12-11 20:21 ` [PATCH v3 2/6] mm cma: rename PF_MEMALLOC_NOCMA to PF_MEMALLOC_PIN Pavel Tatashin
2020-12-14 14:03 ` Michal Hocko
2020-12-15 4:37 ` Pavel Tatashin
2020-12-11 20:21 ` [PATCH v3 3/6] mm: apply per-task gfp constraints in fast path Pavel Tatashin
2020-12-14 14:09 ` Michal Hocko
2020-12-15 5:20 ` Pavel Tatashin
2020-12-15 8:25 ` Michal Hocko [this message]
2020-12-15 17:35 ` Pavel Tatashin
2020-12-11 20:21 ` [PATCH v3 4/6] mm: honor PF_MEMALLOC_PIN for all movable pages Pavel Tatashin
2020-12-14 14:17 ` Michal Hocko
2020-12-15 5:24 ` Pavel Tatashin
2020-12-15 8:27 ` Michal Hocko
2020-12-15 17:28 ` Pavel Tatashin
2020-12-11 20:21 ` [PATCH v3 5/6] mm/gup: migrate pinned pages out of movable zone Pavel Tatashin
2020-12-11 20:23 ` Jason Gunthorpe
2020-12-11 20:40 ` Pavel Tatashin
2020-12-11 20:46 ` Jason Gunthorpe
2020-12-11 21:09 ` Pavel Tatashin
2020-12-11 21:29 ` David Hildenbrand
2020-12-11 21:35 ` Pavel Tatashin
2020-12-11 21:53 ` David Hildenbrand
2020-12-11 23:00 ` Pavel Tatashin
2020-12-12 0:07 ` John Hubbard
2020-12-11 23:50 ` Jason Gunthorpe
2020-12-12 7:29 ` David Hildenbrand
2020-12-14 13:36 ` Jason Gunthorpe
2020-12-14 14:21 ` David Hildenbrand
2020-12-14 14:30 ` Michal Hocko
2020-12-14 14:19 ` Michal Hocko
2020-12-11 20:21 ` [PATCH v3 6/6] memory-hotplug.rst: add a note about ZONE_MOVABLE and page pinning Pavel Tatashin
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