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    SubjectRe: [RFC][PATCH] memcg: change shmem handler.
    On Thu, 03 Jul 2008 12:45:14 +0530
    Balbir Singh <balbir@linux.vnet.ibm.com> wrote:

    > > This patch fixes some mess by
    > > - PAGE_CGROUP_FLAG_CACHE is deleted (and replaced by FLAG_FILE)
    > > - PAGE_CGROUP_FLAG_SHMEM is added.
    > > - add_to_page_cache_nocharge() is added.
    > > This avoids mem_cgroup_charge_cache_page(). This is useful when page is
    > > pre-charged.
    > > - uses add_to_page_cache_nocharge() also in hugemem.
    > > (I think hugemem controller should be independent from memcg.
    > > Balbir, how do you think ?)
    >
    > I am not 100% sure of that right now. I definitely want different control
    > parameters (not included as a part of memory.limit_in_bytes). If there is
    > leverage from memory controller, we could consider adding that to it or a
    > separate controller if that makes more sense.
    >
    Checking PG_compound in mem_cgroup_charge_cache_page() is enough, maybe.
    (If multi-page-file-cache is added, need rework ;)

    > > - PageSwapBacked() is checked.
    > > (A imported patch from Hugh Dickins)
    > >
    > > As result.
    > > - shmem will be in SwapBacked/Active list at first.
    >
    > Good
    >
    > > - memcg has "shmem/tmpfs" counter.
    > >
    >
    > I think this will be useful too (but I need to play with it)
    >
    I've been argued that "if you want to add such a stupid counter, add the
    same parameter to global lru without any overhead."

    I'll postpone this ;) I have many other thing to do.

    But the total number of pages used for shmem is already counted by
    address_space->nr_pages. So, not very difficult for global lru if we can
    walk all inodes of shmem. The problem will be "whether it's worth to do or not"

    Thanks,
    -Kame




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