Date: Tue, 18 Nov 2014 12:11:26 +0900
From: Joonsoo Kim <iamjoonsoo.kim@lge.com>
To: Mel Gorman <mgorman@suse.de>
Cc: Weijie Yang <weijie.yang.kh@gmail.com>,
        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>,
        Johannes Weiner <hannes@cmpxchg.org>, Minchan Kim <minchan@kernel.org>,
        Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>,
        Zhang Yanfei <zhangyanfei@cn.fujitsu.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>, Vlastimil Babka <vbabka@suse.cz>,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        stable@vger.kernel.org
Subject: Re: [PATCH v5 1/4] mm/page_alloc: fix incorrect isolation behavior
 by rechecking migratetype
Message-ID: <20141118031125.GA12197@js1304-P5Q-DELUXE>
References: <1414740330-4086-1-git-send-email-iamjoonsoo.kim@lge.com>
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 <CAL1ERfMxR0BPQ-1hsD+Z-Oizkt4WHzL_rwYmKd2n70R=H0X22Q@mail.gmail.com>
 <20141114103301.GD21422@suse.de>
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On Fri, Nov 14, 2014 at 10:33:01AM +0000, Mel Gorman wrote:
> > > diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> > > index 4593567..3d090af 100644
> > > --- a/include/linux/mmzone.h
> > > +++ b/include/linux/mmzone.h
> > > @@ -431,6 +431,15 @@ struct zone {
> > >          */
> > >         int                     nr_migrate_reserve_block;
> > >
> > > +#ifdef CONFIG_MEMORY_ISOLATION
> > > +       /*
> > > +        * Number of isolated pageblock. It is used to solve incorrect
> > > +        * freepage counting problem due to racy retrieving migratetype
> > > +        * of pageblock. Protected by zone->lock.
> > > +        */
> > > +       unsigned long           nr_isolate_pageblock;
> > > +#endif
> > > +
> > 
> > First sorry for this deferred reply, I see these patches have been merged
> > into the mainline.
> > However, I still have a tiny question:
> > Why use ZONE_PADDING(_pad1_)  seperate it and zone->lock?
> > How about move it to the same cacheline with zone->lock, because it is
> > accessed under zone->lock?
> > 
> 
> zone->lock is currently sharing lines with the data that is frequently
> updated under zone lock and some of the dirty data cache line bouncing has
> completed when the lock is acquired. nr_isolate_pageblock is a read-mostly
> field and in some cases will never be used. It's fine where it is beside
> other read-mostly fields.
> 

My bad...
I don't remember why I decide that place. :/

It seems better to move nr_isolate_pageblock to the same cacheline with
zone->lock, but, as Mel said, it is rarely used field so improvement would
be marginal.

Thanks.
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