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    SubjectRe: [PATCH v4] mm/memcg: try harder to decrease [memory,memsw].limit_in_bytes
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    On 01/15/2018 03:46 PM, Michal Hocko wrote:
    > On Mon 15-01-18 15:30:59, Andrey Ryabinin wrote:
    >>
    >>
    >> On 01/12/2018 03:24 PM, Michal Hocko wrote:
    >>> On Fri 12-01-18 00:59:38, Andrey Ryabinin wrote:
    >>>> On 01/11/2018 07:29 PM, Michal Hocko wrote:
    >>> [...]
    >>>>> I do not think so. Consider that this reclaim races with other
    >>>>> reclaimers. Now you are reclaiming a large chunk so you might end up
    >>>>> reclaiming more than necessary. SWAP_CLUSTER_MAX would reduce the over
    >>>>> reclaim to be negligible.
    >>>>>
    >>>>
    >>>> I did consider this. And I think, I already explained that sort of race in previous email.
    >>>> Whether "Task B" is really a task in cgroup or it's actually a bunch of reclaimers,
    >>>> doesn't matter. That doesn't change anything.
    >>>
    >>> I would _really_ prefer two patches here. The first one removing the
    >>> hard coded reclaim count. That thing is just dubious at best. If you
    >>> _really_ think that the higher reclaim target is meaningfull then make
    >>> it a separate patch. I am not conviced but I will not nack it it either.
    >>> But it will make our life much easier if my over reclaim concern is
    >>> right and we will need to revert it. Conceptually those two changes are
    >>> independent anywa.
    >>>
    >>
    >> Ok, fair point. But what about livelock than? Don't you think that we should
    >> go back to something like in V1 patch to prevent it?
    >
    > I am not sure what do you mean by the livelock here.
    >

    Livelock is when tasks in cgroup constantly allocate reclaimable memory at high rate,
    and user asked to set too low unreachable limit e.g. 'echo 4096 > memory.limit_in_bytes'.

    We will loop indefinitely in mem_cgroup_resize_limit(), because try_to_free_mem_cgroup_pages() != 0
    (as long as cgroup tasks generate new reclaimable pages fast enough).

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