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    SubjectRe: [PATCH 4/4 v4] kernel/fork.c: memory hotplug updates max_threads
    On 02/23, Heinrich Schuchardt wrote:
    >
    > On 23.02.2015 21:54, Oleg Nesterov wrote:
    > >
    > >> And it changes the swapper/0's rlimits. This is pointless after we fork
    > >> /sbin/init.
    >
    > So should writing to /proc/sys/max_threads update the limits of all
    > processes?

    Why?

    No, I think it should not touch rlimits at all.

    > >> It seems to me these patches need some cleanups. Plus I am not sure the
    > >> kernel should update max_threads automatically, we have the "threads-max"
    > >> sysctl.
    >
    > The idea in the original version of fork_init is that max_threads should
    > be chosen such that the memory needed to store the meta-information of
    > max_threads threads should only be 1/8th of the total memory.
    >
    > Somebody adding or removing memory will not necessarily update
    > /proc/sys/kernel/threads-max.
    >
    > This means that if I remove 90 % of the memory I get to a situation
    > where max_threads allows so many threads to be created that the
    > meta-information occupies all memory.
    >
    > With patch 4/4 max_threads is automatically reduced in this case.

    I understand. But I think that if you remove 90 % of the memory you can
    also update /proc/sys/kernel/threads-max.

    And, suppose that admin specially limited max_threads, then you add more
    memory. Should the kernel bump the limit silently?

    And if hotplug should update max_threads, why it doesn't update, say,
    files_stat.max_files?

    IOW, I do not think that kernel should control max_threads after boot.
    But I won't really argue. Just this looks a bit strange to me.

    Oleg.



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