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    SubjectRe: [RFC][PATCH 0/6] memcg updates (05/Nov)
    KAMEZAWA Hiroyuki wrote:
    > Weekly (RFC) update for memcg.
    >
    > This set includes
    >
    > 1. change force_empty to do move account rather than forget all

    I would like this to be selectable, please. We don't want to break behaviour and
    not everyone would like to pay the cost of movement.

    > 2. swap cache handling
    > 3. mem+swap controller kconfig
    > 4. swap_cgroup for rememver swap account information
    > 5. mem+swap controller core
    > 6. synchronize memcg's LRU and global LRU.
    >
    > "1" is already sent, "6" is a newcomer.
    > I'd like to push out "2" or "2-5" in the next week (if no bugs.)
    >
    > after 6, next candidates are
    > - dirty_ratio handler
    > - account move at task move.
    >
    > Some more explanation about purpose of "6". (see details in patch itself)
    > Now, one of complicated logic in memcg is LRU handling. Because the place of
    > lru_head depends on page_cgroup->mem_cgroup pointer, we have to take
    > lock as following even under zone->lru_lock.
    > ==
    > pc = lookup_page_cgroup(page);
    > if (!trylock_page_cgroup(pc))
    > return -EBUSY;
    >
    > if (PageCgroupUsed(pc)) {
    > struct mem_cgroup_per_zone *mz = page_cgroup_zoneinfo(pc);
    > spin_lock_irqsave(&mz->lru_lock, flags);
    > ....some operation on LRU.
    > spin_unlock_irqrestore(&mz->lru_lock, flags);
    > }
    > unlock_page_cgroup(pc);
    > ==
    > Sigh..
    >
    > After "6", page_cgroup's LRU management can be done independently to some extent.
    > == as
    > (zone->lru_lock is held here)
    > pc = lookup_page_cgroup(page);
    > list operation on pc.
    > (unlock zone->lru_lock)
    > ==
    > Maybe good for maintainance and as a bonus, we can make use of isolate_lru_page() when
    > doing some racy operation.
    >
    > isolate_lru_page(page);
    > pc = lookup_page_cgroup(page);
    > do some jobs.
    > putback_lru_page(page);
    >
    > Maybe this will be a help to implement "account move at task move".

    Sounds promising!

    --
    Balbir


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