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    SubjectRe: [PATCH 0/5] [RFC] transfer ASYNC vmscan writeback IO to the flusher threads
    On Fri, Jul 30, 2010 at 12:09:47AM +0800, Jan Kara wrote:
    > On Thu 29-07-10 19:51:42, Wu Fengguang wrote:
    > > Andrew,
    > >
    > > It's possible to transfer ASYNC vmscan writeback IOs to the flusher threads.
    > > This simple patchset shows the basic idea. Since it's a big behavior change,
    > > there are inevitably lots of details to sort out. I don't know where it will
    > > go after tests and discussions, so the patches are intentionally kept simple.
    > >
    > > sync livelock avoidance (need more to be complete, but this is minimal required for the last two patches)
    > > [PATCH 1/5] writeback: introduce wbc.for_sync to cover the two sync stages
    > > [PATCH 2/5] writeback: stop periodic/background work on seeing sync works
    > > [PATCH 3/5] writeback: prevent sync livelock with the sync_after timestamp
    > Well, essentially any WB_SYNC_NONE writeback is still livelockable if you
    > just grow a file constantly. So your changes are a step in the right
    > direction but won't fix the issue completely.

    Right. We have complementary patches to prevent livelocks both inside
    file and among files.

    > But what we could do to fix
    > the issue completely would be to just set wbc->nr_to_write to LONG_MAX
    > before writing inode for sync use my livelock avoidance using page-tagging
    > for this case (it wouldn't have the possible performance issue because we
    > are going to write all the inode anyway).

    Yeah your patches are good to avoid livelocking in one single busy file.
    I didn't forgot them :)

    > I can write the patch but frankly there are so many patches floating
    > around that I'm not sure what I should base it on...

    Me confused too. It may take some time to quiet down..

    Thanks,
    Fengguang


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