Date: Mon, 14 Jul 2014 15:24:23 +0900
From: Joonsoo Kim <iamjoonsoo.kim@lge.com>
To: Vlastimil Babka <vbabka@suse.cz>
Cc: Andrew Morton <akpm@linux-foundation.org>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Rik van Riel <riel@redhat.com>, Peter Zijlstra <peterz@infradead.org>,
        Mel Gorman <mgorman@suse.de>, Johannes Weiner <hannes@cmpxchg.org>,
        Minchan Kim <minchan@kernel.org>,
        Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>,
        Zhang Yanfei <zhangyanfei@cn.fujitsu.com>,
        "Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>,
        Tang Chen <tangchen@cn.fujitsu.com>,
        Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>,
        Wen Congyang <wency@cn.fujitsu.com>,
        Marek Szyprowski <m.szyprowski@samsung.com>,
        Michal Nazarewicz <mina86@mina86.com>,
        Laura Abbott <lauraa@codeaurora.org>,
        Heesub Shin <heesub.shin@samsung.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>,
        Ritesh Harjani <ritesh.list@gmail.com>, t.stanislaws@samsung.com,
        Gioh Kim <gioh.kim@lge.com>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 03/10] mm/page_alloc: handle page on pcp correctly if
 it's pageblock is isolated
Message-ID: <20140714062423.GB11317@js1304-P5Q-DELUXE>
References: <1404460675-24456-1-git-send-email-iamjoonsoo.kim@lge.com>
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 <53BABA94.4040107@suse.cz>
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On Mon, Jul 07, 2014 at 05:19:48PM +0200, Vlastimil Babka wrote:
> On 07/04/2014 09:57 AM, Joonsoo Kim wrote:
> >If pageblock of page on pcp are isolated now, we should free it to isolate
> >buddy list to prevent future allocation on it. But current code doesn't
> >do this.
> >
> >Moreover, there is a freepage counting problem on current code. Although
> >pageblock of page on pcp are isolated now, it could go normal buddy list,
> >because get_onpcp_migratetype() will return non-isolate migratetype.
> 
> get_onpcp_migratetype() is only introduced in later patch.

Yes, I will fix it.

> 
> >In this case, we should do either adding freepage count or changing
> >migratetype to MIGRATE_ISOLATE, but, current code do neither.
> 
> I wouldn't say it "do neither". It already limits the freepage
> counting to !MIGRATE_ISOLATE case (and it's not converted to
> __mod_zone_freepage_state for some reason). So there's accounting
> mismatch in addition to buddy list misplacement.

Okay.

> 
> >This patch fixes these two problems by handling pageblock migratetype
> >before calling __free_one_page(). And, if we find the page on isolated
> >pageblock, change migratetype to MIGRATE_ISOLATE to prevent future
> >allocation of this page and freepage counting problem.
> 
> So although this is not an addition of a new pageblock migratetype
> check to the fast path (the check is already there), I would prefer
> removing the check :) 

Yes, I want to do it if possible. :)

> With the approach of pcplists draining
> outlined in my reply to 00/10, we would allow a misplacement to
> happen (and the page accounted as freepage) immediately followed by
> move_frepages_block which would place the page onto isolate freelist
> with the rest. Anything newly freed will get isolate_migratetype
> determined in free_hot_cold_page or __free_pages_ok (where it would
> need moving the migratepage check under the disabled irq part) and
> be placed and buddy-merged properly.

I explained the problem of this approach in 00/10.

Thanks.

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