linux-kernel - Re: [PATCH 2/4] mm, procfs: account for shmem swap in /proc/pid/smaps

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Date:	Wed, 11 Mar 2015 16:26:50 +0100
From:	Jerome Marchand <jmarchan@...hat.com>
To:	Konstantin Khlebnikov <khlebnikov@...dex-team.ru>,
	Konstantin Khlebnikov <koct9i@...il.com>,
	Vlastimil Babka <vbabka@...e.cz>
CC:	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-doc@...r.kernel.org, Hugh Dickins <hughd@...gle.com>,
	Michal Hocko <mhocko@...e.cz>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Cyrill Gorcunov <gorcunov@...nvz.org>,
	Randy Dunlap <rdunlap@...radead.org>,
	linux-s390@...r.kernel.org,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Paul Mackerras <paulus@...ba.org>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Oleg Nesterov <oleg@...hat.com>
Subject: Re: [PATCH 2/4] mm, procfs: account for shmem swap in /proc/pid/smaps

On 03/11/2015 04:03 PM, Konstantin Khlebnikov wrote:
> On 11.03.2015 15:30, Konstantin Khlebnikov wrote:
>> On Thu, Feb 26, 2015 at 4:51 PM, Vlastimil Babka <vbabka@...e.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.
> 
> Something like that (see patch in attachment)
> 

-8<---

diff --git a/mm/shmem.c b/mm/shmem.c
index cf2d0ca010bc..492f78f51fc2 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1363,6 +1363,13 @@ static struct mempolicy *shmem_get_policy(struct
vm_area_struct *vma,
 }
 #endif

+static unsigned long shmem_get_swap_usage(struct vm_area_struct *vma)
+{
+	struct inode *inode = file_inode(vma->vm_file);
+
+	return SHMEM_I(inode)->swapped;
+}
+
 int shmem_lock(struct file *file, int lock, struct user_struct *user)
 {
 	struct inode *inode = file_inode(file);

-8<---

That will not work for shared anonymous mapping since they all share the
same vm_file (/dev/zero).

Jerome


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