From: Michal Nazarewicz <mina86@mina86.com>
To: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Andrew Morton <akpm@linux-foundation.org>, Gioh Kim <gioh.kim@lge.com>,
        Laura Abbott <lauraa@codeaurora.org>,
        Marek Szyprowski <m.szyprowski@samsung.com>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        =?utf-8?B?7J206rG07Zi4?= <gunho.lee@lge.com>,
        Gi-Oh Kim <gurugio@gmail.com>
Subject: Re: [PATCH] [RFC] CMA: clear buffer-head lru before page migration
In-Reply-To: <20140714070225.GE11317@js1304-P5Q-DELUXE>
Organization: http://mina86.com/
References: <53B664E5.5060102@lge.com> <20140707155252.15e81dff6683393ba3590478@linux-foundation.org> <xa1tpphf4x3s.fsf@mina86.com> <20140714070225.GE11317@js1304-P5Q-DELUXE>
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Date: Mon, 14 Jul 2014 17:25:41 +0200
Message-ID: <xa1t4mykarnu.fsf@mina86.com>
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On Mon, Jul 14 2014, Joonsoo Kim <iamjoonsoo.kim@lge.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.

-- 
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.o. | Liege of Serenely Enlightened Majesty of      o' \,=./ `o
..o | Computer Science,  Michał “mina86” Nazarewicz    (o o)
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