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

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Message-ID: <54C4B680.3010304@suse.cz>
Date:	Sun, 25 Jan 2015 10:25:20 +0100
From:	Vlastimil Babka <vbabka@...e.cz>
To:	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

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?
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