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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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