linux-kernel - [Question] ksm: rmap_item pointing to some stale vmas

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Message-ID: <55268741.8010301@codeaurora.org>
Date:	Thu, 09 Apr 2015 19:35:53 +0530
From:	Susheel Khiani <skhiani@...eaurora.org>
To:	akpm@...ux-foundation.org, peterz@...radead.org, neilb@...e.de,
	dhowells@...hat.com, hughd@...gle.com, paulmcquad@...il.com,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: [Question] ksm: rmap_item pointing to some stale vmas

Hi,

We are seeing an issue during try_to_unmap_ksm where in call to 
try_to_unmap_one is failing.

try_to_unmap_ksm in this particular case is trying to go through vmas 
associated with each rmap_item->anon_vma. What we see is this that the 
corresponding page is not mapped to any of the vmas associated with 2 
rmap_item.

The associated rmap_item in this case looks like pointing to some valid 
vma but the said page is not found to be mapped under it. 
try_to_unmap_one thus fails to find valid ptes for these vmas.

At the same time we can see that the page actually is mapped in 2 
separate and different vmas which are not part of rmap_item associated 
with page.

So whether rmap_item is pointing to some stale vmas and now the mapping 
has changed? Or there is something else going on here.
p
Any pointer would be appreciated.

-- 
Susheel Khiani

QUALCOMM INDIA, on behalf of Qualcomm Innovation Center,
Inc. is a member of the Code Aurora Forum, hosted by The Linux Foundation
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