linux-kernel - Re: [PATCH] [RFC] CMA: clear buffer-head lru before page migration

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Date:	Mon, 14 Jul 2014 17:25:41 +0200
From:	Michal Nazarewicz <mina86@...a86.com>
To:	Joonsoo Kim <iamjoonsoo.kim@....com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Gioh Kim <gioh.kim@....com>,
	Laura Abbott <lauraa@...eaurora.org>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	이건호 <gunho.lee@....com>,
	Gi-Oh Kim <gurugio@...il.com>
Subject: Re: [PATCH] [RFC] CMA: clear buffer-head lru before page migration

On Mon, Jul 14 2014, Joonsoo Kim <iamjoonsoo.kim@....com> wrote:
> On Tue, Jul 08, 2014 at 06:46:31PM +0200, Michal Nazarewicz wrote:
>> This seems reasonable, except I think [invalidate_bh_lrus()] should
>> go after start_isolate_page_range call because otherwise there's no
>> guarantee that someone won't grab those pages back.
>> 
>> Also to avoid the #ifdef perhaps we want this as well:
>
> I think that we just want to remove ifdef CONFIG_CMA on above code
> snippet, because invalidate_bh_lrus() would also help user of
> alloc_contig_range() with MIGRATE_MOVABLE.

Sounds good to me.

>> The purpose is to get free non-buddy pages (so pages on PCP lists for
>> instance) back onto the buddy list.  It's safe to move those calls above
>> the call to __alloc_contig_migrate_range, but I don't think it will
>> change anything (except of course the fact that if migration fails,
>> we'll do the draining for nothing).

> At a glance, we don't need that drain_all_pages(), because
> drain_all_pages() is also called by set_migratetype_isolate() after
> changing migratetype.

You are likely correct.

> And, it is better to move up lru_add_drain_all() to ahead of
> __alloc_contig_migrate_range(), because some pages could be skipped
> to migrate due to this lru page caching mechanism.

Again, sounds good to me.

-- 
Best regards,                                         _     _
.o. | Liege of Serenely Enlightened Majesty of      o' \,=./ `o
..o | Computer Science,  Michał “mina86” Nazarewicz    (o o)
ooo +--<mpn@...gle.com>--<xmpp:mina86@...ber.org>--ooO--(_)--Ooo--
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