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    SubjectRe: [RFC] Shared page accounting for memory cgroup
    On Mon, 4 Jan 2010 06:20:31 +0530
    Balbir Singh <balbir@linux.vnet.ibm.com> wrote:

    > * KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> [2010-01-04 09:35:28]:
    >
    > > On Mon, 4 Jan 2010 05:37:52 +0530
    > > Balbir Singh <balbir@linux.vnet.ibm.com> wrote:
    > >
    > > > * KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> [2010-01-04 08:51:08]:
    > > >
    > > > > On Tue, 29 Dec 2009 23:57:43 +0530
    > > > > Balbir Singh <balbir@linux.vnet.ibm.com> wrote:
    > > > >
    > > > > > Hi, Everyone,
    > > > > >
    > > > > > I've been working on heuristics for shared page accounting for the
    > > > > > memory cgroup. I've tested the patches by creating multiple cgroups
    > > > > > and running programs that share memory and observed the output.
    > > > > >
    > > > > > Comments?
    > > > >
    > > > > Hmm? Why we have to do this in the kernel ?
    > > > >
    > > >
    > > > For several reasons that I can think of
    > > >
    > > > 1. With task migration changes coming in, getting consistent data free of races
    > > > is going to be hard.
    > >
    > > Hmm, Let's see real-worlds's "ps" or "top" command. Even when there are no guarantee
    > > of error range of data, it's still useful.
    >
    > Yes, my concern is this
    >
    > 1. I iterate through tasks and calculate RSS
    > 2. I look at memory.usage_in_bytes
    >
    > If the time in user space between 1 and 2 is large I get very wrong
    > results, specifically if the workload is changing its memory usage
    > drastically.. no?
    >
    No. If it takes long time, locking fork()/exit() for such long time is the bigger
    issue.
    I recommend you to add memacct subsystem to sum up RSS of all processes's RSS counting
    under a cgroup. Althoght it may add huge costs in page fault path but implementation
    will be very simple and will not hurt realtime ops.
    There will be no terrible race, I guess.

    Thanks,
    -Kame



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