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    SubjectRE: [PATCH 03/36] memcg: adjust to support new THP refcounting
    Date
    Kirill A. Shutemov wrote:
    > As with rmap, with new refcounting we cannot rely on PageTransHuge() to
    > check if we need to charge size of huge page form the cgroup. We need to
    > get information from caller to know whether it was mapped with PMD or
    > PTE.
    >
    > We do uncharge when last reference on the page gone. At that point if we
    > see PageTransHuge() it means we need to unchange whole huge page.
    >
    > The tricky part is partial unmap -- when we try to unmap part of huge
    > page. We don't do a special handing of this situation, meaning we don't
    > uncharge the part of huge page unless last user is gone or
    > split_huge_page() is triggered. In case of cgroup memory pressure
    > happens the partial unmapped page will be split through shrinker. This
    > should be good enough.
    >
    > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
    > Tested-by: Sasha Levin <sasha.levin@oracle.com>
    > Acked-by: Vlastimil Babka <vbabka@suse.cz>

    checkpatch fixlet:

    diff --git a/mm/swapfile.c b/mm/swapfile.c
    index 6dd365d1c488..117bedd02db2 100644
    --- a/mm/swapfile.c
    +++ b/mm/swapfile.c
    @@ -1103,8 +1103,8 @@ static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd,
    if (unlikely(!page))
    return -ENOMEM;

    - if (mem_cgroup_try_charge(page, vma->vm_mm, GFP_KERNEL, &memcg, false))
    - {
    + if (mem_cgroup_try_charge(page, vma->vm_mm, GFP_KERNEL,
    + &memcg, false)) {
    ret = -ENOMEM;
    goto out_nolock;
    }

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