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: Fri, 28 Feb 2020 16:17:17 +0100 [thread overview]
Message-ID: <1094fc21-9104-1410-bc03-f1934dbfcd66@suse.cz> (raw)
In-Reply-To: <bd867dba881347a21757fba908f48a6e23e72439.camel@surriel.com>
On 2/26/20 6:53 PM, Rik van Riel wrote:
> On Wed, 2020-02-26 at 10:48 +0100, Vlastimil Babka wrote:
>> On 2/25/20 7:44 PM, Rik van Riel wrote:
>>
>> 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.
>
> You are right, it is not different.
>
> As for lru_add_drain_all(), I wonder at what point that
> should happen?
Right now it seems to be done in alloc_contig_range(), but rather late.
> It appears that the order in which things are done does
> not really provide a good moment:
> 1) decide to attempt allocating a range of memory
> 2) scan each page block for unmovable pages
> 3) if no unmovable pages are found, mark the page block
> MIGRATE_ISOLATE
>
> I wonder if we should do things the opposite way, first
> marking the page block MIGRATE_ISOLATE (to prevent new
> allocations), then scanning it, and calling lru_add_drain_all
> if we encounter a page that looks like it could benefit from
> that.
>
> If we still see unmovable pages after that, it is cheap
> enough to set the page block back to its previous state.
Yeah seems like the whole has_unmovable_pages() thing isn't much useful
here. It might prevent some unnecessary action like isolating something,
then finding non-movable page and rolling back the isolation. But maybe
it's not worth the savings, and also has_unmovable_pages() being false
doesn't guarantee succeed in the actual isolate+migrate attempt. And if
it can cause a false negative due to lru pages not drained, then it's
actually worse than if it wasn't called at all.
next prev parent reply other threads:[~2020-02-28 15:23 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
2020-02-26 17:53 ` Rik van Riel
2020-02-28 15:17 ` Vlastimil Babka [this message]
2020-03-01 2:24 ` Rik van Riel
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