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    SubjectRe: [PATCH 4/6] writeback: sync expired inodes first in background writeback
    On Mon, Jul 26, 2010 at 08:20:54PM +0800, Jan Kara wrote:
    > On Mon 26-07-10 20:00:11, Wu Fengguang wrote:
    > > On Mon, Jul 26, 2010 at 06:57:37PM +0800, Mel Gorman wrote:
    > > > On Thu, Jul 22, 2010 at 01:09:32PM +0800, Wu Fengguang wrote:
    > > > > A background flush work may run for ever. So it's reasonable for it to
    > > > > mimic the kupdate behavior of syncing old/expired inodes first.
    > > > >
    > > > > The policy is
    > > > > - enqueue all newly expired inodes at each queue_io() time
    > > > > - retry with halfed expire interval until get some inodes to sync
    > > > >
    > > > > CC: Jan Kara <jack@suse.cz>
    > > > > Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
    > > >
    > > > Ok, intuitively this would appear to tie into pageout where we want
    > > > older inodes to be cleaned first by background flushers to limit the
    > > > number of dirty pages encountered by page reclaim. If this is accurate,
    > > > it should be detailed in the changelog.
    > >
    > > Good suggestion. I'll add these lines:
    > >
    > > This is to help reduce the number of dirty pages encountered by page
    > > reclaim, eg. the pageout() calls. Normally older inodes contain older
    > > dirty pages, which are more close to the end of the LRU lists. So
    > Well, this kind of implicitely assumes that once page is written, it
    > doesn't get accessed anymore, right?

    No, this patch is not evicting the page :)

    > Which I imagine is often true but
    > not for all workloads... Anyway I think this behavior is a good start
    > also because it is kind of natural to users to see "old" files written
    > first.

    Thanks,
    Fengguang

    > > syncing older inodes first helps reducing the dirty pages reached by
    > > the page reclaim code.
    >
    > Honza
    > --
    > Jan Kara <jack@suse.cz>
    > SUSE Labs, CR


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