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SubjectRe: [PATCH -mm] memcg: fix handling of shmem migration(v2)
On Wed, 17 Sep 2008 16:55:44 +0900
Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> wrote:

> Before this patch, if migrating shmem/tmpfs pages, newpage would be
> charged with PAGE_CGROUP_FLAG_FILE set, while oldpage has been charged
> without the flag.
>
> The problem here is mem_cgroup_move_lists doesn't clear(or set)
> the PAGE_CGROUP_FLAG_FILE flag, so pc->flags of the newpage
> remains PAGE_CGROUP_FLAG_FILE set even when the pc is moved to
> another lru(anon) by mem_cgroup_move_lists. And this leads to
> incorrect MEM_CGROUP_ZSTAT.
> (In my test, I see an underflow of MEM_CGROUP_ZSTAT(active_file).
> As a result, mem_cgroup_calc_reclaim returns very huge number and
> causes soft lockup on page reclaim.)
>
> I'm not sure if mem_cgroup_move_lists should handle PAGE_CGROUP_FLAG_FILE
> or not(I suppose it should be used to move between active <-> inactive,
> not anon <-> file), I added MEM_CGROUP_CHARGE_TYPE_SHMEM for precharge
> at shmem's page migration.
>
>
> ChangeLog: v1->v2
> - instead of modifying migrate.c, modify memcontrol.c only.
> - add MEM_CGROUP_CHARGE_TYPE_SHMEM.
>
>
> Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
> ---
> mm/memcontrol.c | 13 ++++++++++---
> 1 files changed, 10 insertions(+), 3 deletions(-)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 2979d22..ef8812d 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -179,6 +179,7 @@ enum charge_type {
> MEM_CGROUP_CHARGE_TYPE_CACHE = 0,
> MEM_CGROUP_CHARGE_TYPE_MAPPED,
> MEM_CGROUP_CHARGE_TYPE_FORCE, /* used by force_empty */
> + MEM_CGROUP_CHARGE_TYPE_SHMEM, /* used by page migration of shmem */
> };
>
> /*
> @@ -579,8 +580,10 @@ static int mem_cgroup_charge_common(struct page *page, struct mm_struct *mm,
> pc->flags |= PAGE_CGROUP_FLAG_FILE;
> else
> pc->flags |= PAGE_CGROUP_FLAG_ACTIVE;
> - } else
> + } else if (ctype == MEM_CGROUP_CHARGE_TYPE_MAPPED)
> pc->flags = PAGE_CGROUP_FLAG_ACTIVE;
> + else /* MEM_CGROUP_CHARGE_TYPE_SHMEM */
> + pc->flags = PAGE_CGROUP_FLAG_CACHE | PAGE_CGROUP_FLAG_ACTIVE;
>
> lock_page_cgroup(page);
> if (unlikely(page_get_page_cgroup(page))) {
> @@ -739,8 +742,12 @@ int mem_cgroup_prepare_migration(struct page *page, struct page *newpage)
> if (pc) {
> mem = pc->mem_cgroup;
> css_get(&mem->css);
> - if (pc->flags & PAGE_CGROUP_FLAG_CACHE)
> - ctype = MEM_CGROUP_CHARGE_TYPE_CACHE;
> + if (pc->flags & PAGE_CGROUP_FLAG_CACHE) {
> + if (page_is_file_cache(page))
> + ctype = MEM_CGROUP_CHARGE_TYPE_CACHE;
> + else
> + ctype = MEM_CGROUP_CHARGE_TYPE_SHMEM;
> + }
> }
> unlock_page_cgroup(page);
> if (mem) {

I queued this as a fix against
vmscan-split-lru-lists-into-anon-file-sets.patch. Was that appropriate?

If the bug you're fixing here is also present in mainline then I'll
need to ask for a tested patch against mainline, please.





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