linux-kernel - Re: [PATCH] mm: incorporate read-only pages into transparent huge pages

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Message-ID: <54C500F0.3070903@aliyun.com>
Date:	Sun, 25 Jan 2015 22:42:56 +0800
From:	Zhang Yanfei <zhangyanfei.linux@...yun.com>
To:	Vlastimil Babka <vbabka@...e.cz>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Ebru Akagunduz <ebru.akagunduz@...il.com>
CC:	linux-mm@...ck.org, akpm@...ux-foundation.org,
	kirill@...temov.name, mhocko@...e.cz, mgorman@...e.de,
	rientjes@...gle.com, sasha.levin@...cle.com, hughd@...gle.com,
	hannes@...xchg.org, linux-kernel@...r.kernel.org, riel@...hat.com
Subject: Re: [PATCH] mm: incorporate read-only pages into transparent huge
 pages

Hello

在 2015/1/25 17:25, Vlastimil Babka 写道:
> On 23.1.2015 20:18, Andrea Arcangeli wrote:
>>> >+        if (!pte_write(pteval)) {
>>> >+            if (++ro > khugepaged_max_ptes_none)
>>> >+                goto out_unmap;
>>> >+        }
>> It's true this is maxed out at 511, so there must be at least one
>> writable and not none pte (as results of the two "ro" and "none"
>> counters checks).
> 
> Hm, but if we consider ro and pte_none separately, both can be lower
> than 512, but the sum of the two can be 512, so we can actually be in
> read-only VMA?

Yes, I also think so.

So is it necessary to add a at-least-one-writable-pte check just like the existing
at-least-one-page-referenced check?

Thanks.
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