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

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Message-ID: <20130822065038.GA13415@lge.com>
Date:	Thu, 22 Aug 2013 15:50:38 +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

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.

> 
> Also the code will become if you did
> 
> if (!chg && avoid_reserve)
>    chg = 1;
> 
> and then rest of the code will be able to handle the case.


We still pass avoid_reserve to dequeue_huge_page_vma() and check avoid_reserve
there, so maintaining avoid_reserve and checking it separately is better
to understand a logic. And it doesn't matter at all since I eventually unify
these in patch 13.

Thanks.
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