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Date: Wed, 11 Mar 2015 20:10:39 +0100
From: Vlastimil Babka <vbabka@suse.cz>
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Subject: Re: [PATCH 2/4] mm, procfs: account for shmem swap in /proc/pid/smaps
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To: Konstantin Khlebnikov <koct9i@gmail.com>
Cc: "linux-mm@kvack.org" <linux-mm@kvack.org>, Jerome Marchand <jmarchan@redhat.com>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, Andrew Morton <akpm@linux-foundation.org>, linux-doc@vger.kernel.org, Hugh Dickins <hughd@google.com>, Michal Hocko <mhocko@suse.cz>, "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>, Cyrill Gorcunov <gorcunov@openvz.org>, Randy Dunlap <rdunlap@infradead.org>, linux-s390@vger.kernel.org, Martin Schwidefsky <schwidefsky@de.ibm.com>, Heiko Carstens <heiko.carstens@de.ibm.com>, Peter Zijlstra <peterz@infradead.org>, Paul Mackerras <paulus@samba.org>, Arnaldo Carvalho de Melo <acme@kernel.org>, Oleg Nesterov <oleg@redhat.com>
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On 03/11/2015 01:30 PM, Konstantin Khlebnikov wrote:
> On Thu, Feb 26, 2015 at 4:51 PM, Vlastimil Babka <vbabka@suse.cz> wrote:
>> Currently, /proc/pid/smaps will always show "Swap: 0 kB" for shmem-backed
>> mappings, even if the mapped portion does contain pages that were swapped out.
>> This is because unlike private anonymous mappings, shmem does not change pte
>> to swap entry, but pte_none when swapping the page out. In the smaps page
>> walk, such page thus looks like it was never faulted in.
>
> Maybe just add count of swap entries allocated by mapped shmem into
> swap usage of this vma? That's isn't exactly correct for partially
> mapped shmem but this is something weird anyway.

Yeah for next version I want to add a patch optimizing for the 
(hopefully) common cases:

1. SHMEM_I(inode)->swapped is 0 - no need to consult radix tree
2. shmem inode is mapped fully (I hope it's ok to just compare its size 
and mapping size) - just use the value of SHMEM_I(inode)->swapped like 
you suggest



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