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    SubjectRe: [RFC][PATCH v7 08/14] writeback: add memcg fields to writeback_control
    On Fri, May 13, 2011 at 2:41 AM, KAMEZAWA Hiroyuki
    <kamezawa.hiroyu@jp.fujitsu.com> wrote:
    > On Fri, 13 May 2011 01:47:47 -0700
    > Greg Thelen <gthelen@google.com> wrote:
    >
    >> Add writeback_control fields to differentiate between bdi-wide and
    >> per-cgroup writeback.  Cgroup writeback is also able to differentiate
    >> between writing inodes isolated to a particular cgroup and inodes shared
    >> by multiple cgroups.
    >>
    >> Signed-off-by: Greg Thelen <gthelen@google.com>
    >
    > Personally, I want to see new flags with their usage in a patch...

    Ok. Next version will merge the flag definition with first usage of the flag.

    >> ---
    >>  include/linux/writeback.h |    2 ++
    >>  1 files changed, 2 insertions(+), 0 deletions(-)
    >>
    >> diff --git a/include/linux/writeback.h b/include/linux/writeback.h
    >> index d10d133..4f5c0d2 100644
    >> --- a/include/linux/writeback.h
    >> +++ b/include/linux/writeback.h
    >> @@ -47,6 +47,8 @@ struct writeback_control {
    >>       unsigned for_reclaim:1;         /* Invoked from the page allocator */
    >>       unsigned range_cyclic:1;        /* range_start is cyclic */
    >>       unsigned more_io:1;             /* more io to be dispatched */
    >> +     unsigned for_cgroup:1;          /* enable cgroup writeback */
    >> +     unsigned shared_inodes:1;       /* write inodes spanning cgroups */
    >>  };
    >
    >
    > If shared_inode is really rare case...we don't need to have this shared_inodes
    > flag and do writeback shared_inode always.....No ?
    >
    > Thanks,
    > -Kame

    The shared_inodes field is present to avoid punishing cgroups that are
    not sharing, if they are run on a system that also includes sharing.

    This issue is being debated in another thread: "[RFC][PATCH v7 00/14]
    memcg: per cgroup dirty page accounting". Depending on the decision,
    we may be able to delete the shared_inode fields if we choose to
    always write shared inodes in both cgroup foreground and cgroup
    background writeback.
    --
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