linux-kernel - Re: [PATCH v2 03/20] mm, hugetlb: fix subpool accounting handling

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Date:	Tue, 27 Aug 2013 16:40:17 +0900
From:	Joonsoo Kim <iamjoonsoo.kim@....com>
To:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>, Mel Gorman <mgorman@...e.de>,
	Michal Hocko <mhocko@...e.cz>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Hugh Dickins <hughd@...gle.com>,
	Davidlohr Bueso <davidlohr.bueso@...com>,
	David Gibson <david@...son.dropbear.id.au>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Wanpeng Li <liwanp@...ux.vnet.ibm.com>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	Hillf Danton <dhillf@...il.com>
Subject: Re: [PATCH v2 03/20] mm, hugetlb: fix subpool accounting handling

On Mon, Aug 26, 2013 at 06:31:35PM +0530, Aneesh Kumar K.V wrote:
> Joonsoo Kim <iamjoonsoo.kim@....com> writes:
> 
> > On Thu, Aug 22, 2013 at 12:38:12PM +0530, Aneesh Kumar K.V wrote:
> >> Joonsoo Kim <iamjoonsoo.kim@....com> writes:
> >> 
> >> > Hello, Aneesh.
> >> >
> >> > First of all, thank you for review!
> >> >
> >> > On Wed, Aug 21, 2013 at 02:58:20PM +0530, Aneesh Kumar K.V wrote:
> >> >> Joonsoo Kim <iamjoonsoo.kim@....com> writes:
> >> >> 
> >> >> > If we alloc hugepage with avoid_reserve, we don't dequeue reserved one.
> >> >> > So, we should check subpool counter when avoid_reserve.
> >> >> > This patch implement it.
> >> >> 
> >> >> Can you explain this better ? ie, if we don't have a reservation in the
> >> >> area chg != 0. So why look at avoid_reserve. 
> >> >
> >> > We don't consider avoid_reserve when chg != 0.
> >> > Look at following code.
> >> >
> >> > +       if (chg || avoid_reserve)
> >> > +               if (hugepage_subpool_get_pages(spool, 1))
> >> >
> >> > It means that if chg != 0, we skip to check avoid_reserve.
> >> 
> >> when whould be avoid_reserve == 1 and chg == 0 ?
> >
> > In this case, we should do hugepage_subpool_get_pages(), since we don't
> > get a reserved page due to avoid_reserve.
> 
> As per off-list discussion we had around this, please add additional
> information in commit message explaining when we have
> avoid_reserve == 1 and chg == 0

Okay!

> 
> Something like the below copied from call site.
> 
> 	 /* If the process that created a MAP_PRIVATE mapping is about to
> 	  * perform a COW due to a shared page count, attempt to satisfy
> 	  * the allocation without using the existing reserves
>           */
> 
> Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@...ux.vnet.ibm.com>

Thanks.
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