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    SubjectRe: [Lsf10-pc] [LFS/VM TOPIC] Stable pages while IO (was Wrong DIF guard tag on ext2 write)
    On Fri 04-06-10 12:30:09, J. Bruce Fields wrote:
    > On Fri, Jun 04, 2010 at 06:23:32PM +0200, Jan Kara wrote:
    > > On Thu 03-06-10 19:09:52, Boaz Harrosh wrote:
    > > > [Topic]
    > > > How to not let pages change while in IO
    > > >
    > > > [Abstract]
    > > > As seen in a long thread on the fsdvel scsi mailing lists. Lots of
    > > > people have headaches and sleep less nights because individual pages
    > > > can change while in IO and/or DMA. Though each one as slightly different
    > > > needs, the mechanics look to be the same.
    > > Hmm, I don't think it's really about "how to not let pages change" - that
    > > is doable by using wait_on_page_writeback() in ->page_mkwrite and
    > > ->write_begin.
    > Will the same work for the NFS server checksumming page data in read
    > replies?
    Currently it won't. The above relies on the fact that when we clear dirty
    page flag in clear_page_dirty_for_io we also write-protect the page.
    Moreover I suppose you don't set PageWriteback when serving a content from
    a page...
    But an elegant way to solve this would IMHO be to do:
    if (page_mkclean(page))
    and now you can be sure that until you unlock the page it cannot be
    modified because both ->page_mkwrite and ->write_begin need page lock
    before they can go and modify a page...

    Jan Kara <>
    SUSE Labs, CR

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