[lkml]   [2008]   [Jun]   [19]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
    SubjectRe: [patch] aio: invalidate async directio writes
    On Wed, 2008-06-18 at 14:09 -0400, Jeff Moyer wrote:
    > Hi, Andrew,
    > This is a follow-up to:
    > commit bdb76ef5a4bc8676a81034a443f1eda450b4babb
    > Author: Zach Brown <>
    > Date: Tue Oct 30 11:45:46 2007 -0700
    > dio: fix cache invalidation after sync writes
    > Commit commit 65b8291c4000e5f38fc94fb2ca0cb7e8683c8a1b ("dio: invalidate
    > clean pages before dio write") introduced a bug which stopped dio from
    > ever invalidating the page cache after writes. It still invalidated it
    > before writes so most users were fine.
    > Karl Schendel reported ( ) hitting
    > this bug when he had a buffered reader immediately reading file data
    > after an O_DIRECT [writer] had written the data. The kernel issued
    > read-ahead beyond the position of the reader which overlapped with the
    > O_DIRECT writer. The failure to invalidate after writes caused the
    > reader to see stale data from the read-ahead.
    > The following patch is originally from Karl. The following commentary
    > is his:
    > The below 3rd try takes on your suggestion of just invalidating
    > no matter what the retval from the direct_IO call. I ran it
    > thru the test-case several times and it has worked every time.
    > The post-invalidate is probably still too early for async-directio,
    > but I don't have a testcase for that; just sync. And, this
    > won't be any worse in the async case.
    > I added a test to the aio-dio-regress repository which mimics Karl's IO
    > pattern. It verifed the bad behaviour and that the patch fixed it. I
    > agree with Karl, this still doesn't help the case where a buffered
    > reader follows an AIO O_DIRECT writer. That will require a bit more
    > work.
    > This gives up on the idea of returning EIO to indicate to userspace that
    > stale data remains if the invalidation failed.
    > Note the second-to-last paragraph, where it mentions that this does not fix
    > the AIO case. I updated the regression test to also perform asynchronous
    > I/O and verified that the problem does exist.
    > To fix the problem, we need to invalidate the pages that were under write
    > I/O after the I/O completes. Because the I/O completion handler can be called
    > in interrupt context (and invalidate_inode_pages2 cannot be called in interrupt
    > context), this patch opts to defer the completion to a workqueue. That
    > workqueue is responsible for invalidating the page cache pages and completing
    > the I/O.
    > I verified that the test case passes with the following patch applied.

    I'm utterly ignorant of all thing [AD]IO, but doesn't deferring the
    invalidate open up/widen a race window?

     \ /
      Last update: 2008-06-19 09:55    [W:0.034 / U:5.680 seconds]
    ©2003-2017 Jasper Spaans. hosted at Digital OceanAdvertise on this site