lkml.org 
[lkml]   [2012]   [Mar]   [8]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH v3 2/2] memcg: avoid THP split in task migration
    On Fri, 9 Mar 2012 12:24:48 +0900
    KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:

    > On Thu, 8 Mar 2012 18:33:14 -0800 (PST)
    > Hugh Dickins <hughd@google.com> wrote:
    >
    > > On Fri, 9 Mar 2012, KAMEZAWA Hiroyuki wrote:
    > > > > +
    > > > > + page = pmd_page(pmd);
    > > > > + VM_BUG_ON(!page || !PageHead(page));
    > > > > + if (!move_anon() || page_mapcount(page) != 1)
    > > > > + return 0;
    > > >
    > > > Could you add this ?
    > > > ==
    > > > static bool move_check_shared_map(struct page *page)
    > > > {
    > > > /*
    > > > * Handling of shared pages between processes is a big trouble in memcg.
    > > > * Now, we never move shared-mapped pages between memcg at 'task' moving because
    > > > * we have no hint which task the page is really belongs to. For example,
    > > > * When a task does "fork()-> move to the child other group -> exec()", the charges
    > > > * should be stay in the original cgroup.
    > > > * So, check mapcount to determine we can move or not.
    > > > */
    > > > return page_mapcount(page) != 1;
    > > > }
    > >
    > > That's a helpful elucidation, thank you. However...
    > >
    > > That is not how it has actually been behaving for the last 18 months
    > > (because of the "> 2" bug), so in practice you are asking for a change
    > > in behaviour there.
    > >
    > Yes.
    >
    >
    > > And it's not how it has been and continues to behave with file pages.
    > >
    > It's ok to add somethink like..
    >
    > if (PageAnon(page) && !move_anon())
    > return false;
    > ...
    >
    > > Isn't getting that behaviour in fork-move-exec just a good reason not
    > > to set move_charge_at_immigrate?
    > >
    > Hmm. Maybe.
    >
    > > I think there are other scenarios where you do want all the pages to
    > > move if move_charge_at_immigrate: and that's certainly easier to
    > > describe and to understand and to code.
    > >
    > > But if you do insist on not moving the shared, then it needs to involve
    > > something like mem_cgroup_count_swap_user() on PageSwapCache pages,
    > > rather than just the bare page_mapcount().
    > >
    >
    > This 'moving swap account' was a requirement from a user (NEC?).
    > But no user doesn't say 'I want to move shared pages between cgroups at task
    > move !' and I don't like to move shared objects.
    >
    > > I'd rather delete than add code here!
    > >
    >
    > As a user, for Fujitsu, I believe it's insane to move task between cgroups.
    > So, I have no benefit from this code, at all.
    > Ok, maybe I'm not a stakeholder,here.
    >

    Considering again, in my personal opinion,
    at fork() -> move() -> exec(), parent's RSS charge should not be moved.

    Thanks,
    -Kame



    \
     
     \ /
      Last update: 2012-03-09 05:05    [W:0.026 / U:31.324 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site