linux-kernel - Re: [PATCH v2] mm: incorporate read-only pages into transparent huge pages

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Message-ID: <20150126152509.GT11755@redhat.com>
Date:	Mon, 26 Jan 2015 16:25:09 +0100
From:	Andrea Arcangeli <aarcange@...hat.com>
To:	Vlastimil Babka <vbabka@...e.cz>
Cc:	Ebru Akagunduz <ebru.akagunduz@...il.com>, 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 v2] mm: incorporate read-only pages into transparent huge
 pages

On Mon, Jan 26, 2015 at 04:19:06PM +0100, Andrea Arcangeli wrote:
> Overall I don't see how we could collapse in readonly vma and where
> the bug is for this case, but I may be overlooking something obvious.

I just realized what the problem was... that the "ro" is not the total
number of readonly ptes mapped by the pmd,.. because we don't count
the none ones as readonly too.

It misses a ro increase or equivalent adjustment:

		if (pte_none(pteval)) {
+			ro++;
			if (++none <= khugepaged_max_ptes_none)
[..]

Andrea
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