Re: [PATCH] smaps: fix dirty pages accounting

Hugh Dickins
2010-09-16T16:56:50Z

On Thu, 16 Sep 2010, KOSAKI Motohiro wrote:

> Currently, /proc/<pid>/smaps have wrong dirty pages accounting.
> Shared_Dirty and Private_Dirty output only pte dirty pages and
> ignore PG_dirty page flag. It is difference against documentation,
> but also inconsistent against Referenced field. (Referenced checks
> both pte and page flags)
>
> This patch fixes it.
>
> Test program:
>
> large-array.c
> ---------------------------------------------------
> #include <stdio.h>
> #include <stdlib.h>
> #include <string.h>
> #include <unistd.h>
>
> char array[1*1024*1024*1024L];
>
> int main(void)
> {
> memset(array, 1, sizeof(array));
> pause();
>
> return 0;
> }
> ---------------------------------------------------
>
> Test case:
> 1. run ./large-array
> 2. cat /proc/`pidof large-array`/smaps
> 3. swapoff -a
> 4. cat /proc/`pidof large-array`/smaps again
>
> Test result:
> <before patch>
>
> 00601000-40601000 rw-p 00000000 00:00 0
> Size: 1048576 kB
> Rss: 1048576 kB
> Pss: 1048576 kB
> Shared_Clean: 0 kB
> Shared_Dirty: 0 kB
> Private_Clean: 218992 kB <-- showed pages as clean incorrectly
> Private_Dirty: 829584 kB
> Referenced: 388364 kB
> Swap: 0 kB
> KernelPageSize: 4 kB
> MMUPageSize: 4 kB
>
> <after patch>
>
> 00601000-40601000 rw-p 00000000 00:00 0
> Size: 1048576 kB
> Rss: 1048576 kB
> Pss: 1048576 kB
> Shared_Clean: 0 kB
> Shared_Dirty: 0 kB
> Private_Clean: 0 kB
> Private_Dirty: 1048576 kB <-- fixed
> Referenced: 388480 kB
> Swap: 0 kB
> KernelPageSize: 4 kB
> MMUPageSize: 4 kB
>
> Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>

Certainly you can have my

Acked-by: Hugh Dickins <hughd@google.com>

but I think it's for Matt to decide what he's wanting to show there,
and whether it's safe to change after all this time. I hadn't noticed
the descrepancy between "dirty" and "referenced", that certainly argues
for your patch.

> ---
> fs/proc/task_mmu.c | 4 ++--
> 1 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index 439fc1f..7415f13 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -362,13 +362,13 @@ static int smaps_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
> mss->referenced += PAGE_SIZE;
> mapcount = page_mapcount(page);
> if (mapcount >= 2) {
> - if (pte_dirty(ptent))
> + if (pte_dirty(ptent) || PageDirty(page))
> mss->shared_dirty += PAGE_SIZE;
> else
> mss->shared_clean += PAGE_SIZE;
> mss->pss += (PAGE_SIZE << PSS_SHIFT) / mapcount;
> } else {
> - if (pte_dirty(ptent))
> + if (pte_dirty(ptent) || PageDirty(page))
> mss->private_dirty += PAGE_SIZE;
> else
> mss->private_clean += PAGE_SIZE;
> --
> 1.6.5.2