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    SubjectRe: [RFC] ps command race fix
    On Mon, 24 Jul 2006 19:33:18 -0700
    Andrew Morton <akpm@osdl.org> wrote:

    > On Tue, 25 Jul 2006 11:08:35 +0900
    > KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:
    >
    > > > Then the seek and read and such semantics are nice and stable and
    > > > simple.
    > > >
    > > yes...
    > > I think snapshot at open() is okay.
    >
    > We cannot do a single kmalloc() like cpuset does.
    >
    > The kernel presently kind-of guarantees that a 32k kmalloc() will work,
    > although the VM might have to do very large amounts of work to achieve it.
    >
    > But 32k is only 8192 processes, so a snapshot will need multiple
    > allocations and a list and trouble dropping and retaking tasklist_lock to
    > allocate memory and keeping things stable while doing that. I suspect
    > it'll end up ugly.
    >

    Hm, how about using bitmap instead of table ? (we'll have many holes but...)
    Implementing
    - sytem-wide bitmap of used tgid which is updated only when /proc is opened
    seems not to be much problem. 32k kmalloc can store 256k pids.

    BTW, how large pids and how many proccess in a (heavy and big) system ?

    -Kame

    -
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