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    Subject[RFC 26/43] mm: shmem: when inserting, handle pages already charged to a memcg
    Date
    If shmem_insert_page() is called to insert a page that was preserved
    using PKRAM on the current boot (i.e. preserved page is restored without
    an intervening kexec boot), the page will still be charged to a memory
    cgroup because it is never freed. Don't try to charge it again.

    Signed-off-by: Anthony Yznaga <anthony.yznaga@oracle.com>
    ---
    mm/shmem.c | 21 +++++++++++++--------
    1 file changed, 13 insertions(+), 8 deletions(-)

    diff --git a/mm/shmem.c b/mm/shmem.c
    index 13475073fb52..1f3b43b8fa34 100644
    --- a/mm/shmem.c
    +++ b/mm/shmem.c
    @@ -693,6 +693,7 @@ int shmem_insert_page(struct mm_struct *mm, struct inode *inode, pgoff_t index,
    struct mem_cgroup *memcg;
    pgoff_t hindex = index;
    bool on_lru = PageLRU(page);
    + bool has_memcg = page->mem_cgroup ? true : false;

    if (index > (MAX_LFS_FILESIZE >> PAGE_SHIFT))
    return -EFBIG;
    @@ -738,20 +739,24 @@ int shmem_insert_page(struct mm_struct *mm, struct inode *inode, pgoff_t index,

    __SetPageReferenced(page);

    - err = mem_cgroup_try_charge_delay(page, mm, gfp, &memcg,
    - PageTransHuge(page));
    - if (err)
    - goto out_unlock;
    + if (!has_memcg) {
    + err = mem_cgroup_try_charge_delay(page, mm, gfp, &memcg,
    + PageTransHuge(page));
    + if (err)
    + goto out_unlock;
    + }

    err = shmem_add_to_page_cache(page, mapping, hindex,
    NULL, gfp & GFP_RECLAIM_MASK);
    if (err) {
    - mem_cgroup_cancel_charge(page, memcg,
    - PageTransHuge(page));
    + if (!has_memcg)
    + mem_cgroup_cancel_charge(page, memcg,
    + PageTransHuge(page));
    goto out_unlock;
    }
    - mem_cgroup_commit_charge(page, memcg, on_lru,
    - PageTransHuge(page));
    + if (!has_memcg)
    + mem_cgroup_commit_charge(page, memcg, on_lru,
    + PageTransHuge(page));

    if (!on_lru)
    lru_cache_add_anon(page);
    --
    2.13.3
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