linux-kernel - Re: [PATCH 05/10] mm/page_alloc: optimize and unify pageblock migratetype check in free path

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Date:	Mon, 14 Jul 2014 15:28:52 +0900
From:	Joonsoo Kim <iamjoonsoo.kim@....com>
To:	Vlastimil Babka <vbabka@...e.cz>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Rik van Riel <riel@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Mel Gorman <mgorman@...e.de>,
	Johannes Weiner <hannes@...xchg.org>,
	Minchan Kim <minchan@...nel.org>,
	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>,
	Zhang Yanfei <zhangyanfei@...fujitsu.com>,
	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>,
	Tang Chen <tangchen@...fujitsu.com>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
	Wen Congyang <wency@...fujitsu.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Michal Nazarewicz <mina86@...a86.com>,
	Laura Abbott <lauraa@...eaurora.org>,
	Heesub Shin <heesub.shin@...sung.com>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Ritesh Harjani <ritesh.list@...il.com>,
	t.stanislaws@...sung.com, Gioh Kim <gioh.kim@....com>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 05/10] mm/page_alloc: optimize and unify pageblock
 migratetype check in free path

On Mon, Jul 07, 2014 at 05:50:09PM +0200, Vlastimil Babka wrote:
> On 07/04/2014 09:57 AM, Joonsoo Kim wrote:
> >Currently, when we free the page from pcp list to buddy, we check
> >pageblock of the page in order to isolate the page on isolated
> >pageblock. Although this could rarely happen and to check migratetype of
> >pageblock is somewhat expensive, we check it on free fast path. I think
> >that this is undesirable. To prevent this situation, I introduce new
> >variable, nr_isolate_pageblock on struct zone and use it to determine
> >if we should check pageblock migratetype. Isolation on pageblock rarely
> >happens so we can mostly avoid this pageblock migratetype check.
> 
> Better, but still there's a zone flag check and maintenance. So if
> it could be avoided, it would be better.
> 
> >Additionally, unify freepage counting code, because it can be done in
> >common part, __free_one_page(). This unifying provides extra guarantee
> >that the page on isolate pageblock don't go into non-isolate buddy list.
> >This is similar situation describing in previous patch so refer it
> >if you need more explanation.
> 
> You should make it clearer that you are solving misplacement of the
> type "page should be placed on isolated freelist but it's not"
> through free_one_page(), which was solved only for
> free_pcppages_bulk() in patch 03/10. Mentioning patch 04/10 here,
> which solves the opposite problem "page shouldn't be placed on
> isolated freelist, but it is", only confuses the situation. Also
> this patch undoes everything of 04/10 and moves it elsewhere, so
> that would make it harder to git blame etc. I would reorder 04 and
> 05.

Okay. I will clarify what I am solving in commit description and
reorder patches appropriately.

Thanks.

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