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    SubjectRe: [PATCH] oom: handle overflow in mem_cgroup_out_of_memory()
    On Wed, 26 Jan 2011 12:32:04 -0800
    Greg Thelen <> wrote:

    > > That being said, does this have any practical impact at all? I mean,
    > > this code runs when the cgroup limit is breached. But if the number
    > > of allowed pages (not bytes!) can not fit into 32 bits, it means you
    > > have a group of processes using more than 16T. On a 32-bit machine.
    > The value of this patch is up for debate. I do not have an example
    > situation where this truncation causes the wrong thing to happen. I
    > suppose it might be possible for a racing update to
    > memory.limit_in_bytes which grows the limit from a reasonable (example:
    > 100M) limit to a large limit (example 1<<45) could benefit from this
    > patch. I admit that this case seems pathological and may not be likely
    > or even worth bothering over. If neither the memcg nor the oom
    > maintainers want the patch, then feel free to drop it. I just noticed
    > the issue and thought it might be worth addressing.

    Ah. I was scratching my head over that.

    In zillions of places the kernel assumes that a 32-bit kernel has less
    than 2^32 pages of memory, so the code as it stands is, umm, idiomatic.

    But afaict the only way the patch makes a real-world difference is if
    res_counter_read_u64() is busted?

    And, as you point out, res_counter_read_u64() is indeed busted on
    32-bit machines. It has 25 callsites in mm/memcontrol.c - has anyone
    looked at the implications of this? What happens in all those
    callsites if the counter is read during a count rollover?

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      Last update: 2011-01-26 23:33    [W:0.023 / U:1.008 seconds]
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