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    SubjectRe: [jffs2] [rfc] fix write deadlock regression
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    Jason, thank you _so_ much for finding the underlying cause of this.

    On Sun, 2007-09-02 at 06:20 +0200, Nick Piggin wrote:
    > Hmm, thanks for that. It does sound like it is deadlocking via
    > commit_write(). OTOH, it seems like it could be using the page
    > before it is uptodate -- it _may_ only be dealing with uptodate
    > data at that point... but if so, why even read_cache_page at
    > all?

    jffs2_readpage() is synchronous -- there's no chance that the page won't
    be up to date. We're doing this for garbage collection -- if there are
    many log entries covering a single page of data, we want to write out a
    single replacement which covers the whole page, obsoleting the previous
    suboptimal representation of the same data.

    > However, it is a regression. So unless David can come up with a
    > more satisfactory approach, I guess we'd have to go with your
    > patch.

    I think Jason's patch is the best answer for the moment. At some point
    in the very near future I want to improve the RAM usage and compression
    ratio by dropping the rule that data nodes may not cross page boundaries
    -- in which case garbage collection will need to do something other than
    reading the page using read_cache_page() and then writing it out again;
    it'll probably need to end up using its own internal buffer. But for
    now, Jason's patch looks good.

    Thanks.

    --
    dwmw2

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