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

[Jerome Marchand <jmarchan@redhat.com>]

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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@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.
> 
> 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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