From: Vlastimil Babka <vbabka@suse.cz>
To: Rik van Riel <riel@surriel.com>, linux-kernel@vger.kernel.org
Cc: kernel-team@fb.com, akpm@linux-foundation.org,
linux-mm@kvack.org, mhocko@kernel.org,
mgorman@techsingularity.net, rientjes@google.com,
aarcange@redhat.com
Subject: Re: [PATCH 2/2] mm,thp,compaction,cma: allow THP migration for CMA allocations
Date: Wed, 26 Feb 2020 10:48:37 +0100 [thread overview]
Message-ID: <81c8d2fa-a8ae-82b8-f359-bba055fbff68@suse.cz> (raw)
In-Reply-To: <b3529cfa33f55d47aa2e017c8b0291395c302a02.camel@surriel.com>
On 2/25/20 7:44 PM, Rik van Riel wrote:
>> Also PageTransHuge() is basically just a PageHead() so for each
>> non-hugetlbfs compound page this will assume it's a THP, while
>> correctly
>> it should reach the __PageMovable() || PageLRU(page) tests below.
>>
>> So probably this should do something like.
>>
>> if (PageHuge(page) || PageTransCompound(page)) {
>> ...
>> if (PageHuge(page) && !hpage_migration_supported)) return page.
>
> So far so good.
>
>> if (!PageLRU(head) && !__PageMovable(head)) return page
>
> I don't get this one, though. What about a THP that has
> not made it onto the LRU list yet for some reason?
Uh, is it any different from base pages which have to pass the same check? I
guess the caller could do e.g. lru_add_drain_all() first.
> I don't think anonymous pages are marked __PageMovable,
> are they? It looks like they only have the PAGE_MAPPING_ANON
> flag set, not the PAGE_MAPPING_MOVABLE one.
>
> What am I missing?
My point is that we should not accept compound pages that are neither a
migratable hugetlbfs page nor a THP, as movable. And your PageTransHuge() test
and my PageTransCompound() is really just a test for all compound pages, not
"hugetlbfs or THP only". I should have perhaps suggested PageCompound() instead
of the PageTransCompound() wrapper, to make it more obvious.
So we should test non-hugetlbfs pages first whether they are the kind of
compound pages that are migratable. THP's should pass this test by PageLRU(),
other compound movable pages by __PageMovable(head).
>
>> ...
>>
>> > struct page *head = compound_head(page);
>> > unsigned int skip_pages;
>> >
>> > - if
>> > (!hugepage_migration_supported(page_hstate(head)))
>> > + if (PageHuge(page) &&
>> > + !hugepage_migration_supported(page_hstate(h
>> > ead)))
>> > return page;
>> >
>> > skip_pages = compound_nr(head) - (page - head);
>> >
>>
>>
>
next prev parent reply other threads:[~2020-02-26 9:48 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-21 21:53 [PATCH 0/2] fix THP migration for CMA allocations Rik van Riel
2020-02-21 21:53 ` [PATCH 1/2] mm,compaction,cma: add alloc_contig flag to compact_control Rik van Riel
2020-02-24 15:04 ` Vlastimil Babka
2020-02-21 21:53 ` [PATCH 2/2] mm,thp,compaction,cma: allow THP migration for CMA allocations Rik van Riel
2020-02-21 22:31 ` Zi Yan
2020-02-21 22:35 ` Rik van Riel
2020-02-24 15:29 ` Vlastimil Babka
2020-02-25 18:44 ` Rik van Riel
2020-02-26 9:48 ` Vlastimil Babka [this message]
2020-02-26 17:53 ` Rik van Riel
2020-02-28 15:17 ` Vlastimil Babka
2020-03-01 2:24 ` Rik van Riel
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