linux-kernel - Re: [PATCH v2 2/8] mm/page_alloc: correct to clear guard attribute in DEBUG

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Date:	Wed, 13 Aug 2014 17:20:57 +0900
From:	Joonsoo Kim <iamjoonsoo.kim@....com>
To:	Minchan Kim <minchan@...nel.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Rik van Riel <riel@...hat.com>, Mel Gorman <mgorman@...e.de>,
	Johannes Weiner <hannes@...xchg.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 v2 2/8] mm/page_alloc: correct to clear guard attribute
 in DEBUG_PAGEALLOC

On Tue, Aug 12, 2014 at 01:45:23AM +0000, Minchan Kim wrote:
> On Wed, Aug 06, 2014 at 04:18:30PM +0900, Joonsoo Kim wrote:
> > In __free_one_page(), we check the buddy page if it is guard page.
> > And, if so, we should clear guard attribute on the buddy page. But,
> > currently, we clear original page's order rather than buddy one's.
> > This doesn't have any problem, because resetting buddy's order
> > is useless and the original page's order is re-assigned soon.
> > But, it is better to correct code.
> > 
> > Additionally, I change (set/clear)_page_guard_flag() to
> > (set/clear)_page_guard() and makes these functions do all works
> > needed for guard page. This may make code more understandable.
> > 
> > One more thing, I did in this patch, is that fixing freepage accounting.
> > If we clear guard page and link it onto isolate buddy list, we should
> > not increase freepage count.
> 
> You are saying just "shouldn't do that" but don't say "why" and "result"
> I know the reason but as you know, I'm one of the person who is rather
> familiar with this part but I guess others should spend some time to get.
> Kind detail description is never to look down on person. :)

Hmm. In fact, the reason is already mentioned in cover letter, but,
it is better to write it here.

Will do.

> > 
> 
> Nice catch, Joonsoo! But what make me worry is is this patch makes 3 thing
> all at once.
> 
> 1. fix - no candidate for stable
> 2. clean up
> 3. fix - candidate for stable.
> 
> Could you separate 3 and (1,2) in next spin?
> 

Okay!

Thanks.
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