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    SubjectRe: [CFT][PATCH] block_write_*_buffer rewrite

    On Wed, 1 Dec 1999, Ingo Molnar wrote:

    > On Tue, 30 Nov 1999, Alexander Viro wrote:
    > > Patch merges most of block_write_{partial,cont}_page and fixes a
    > > couple of bad bugs in the latter. It should fix the problems with
    > > write-beyond-EOF on FAT and HPFS and it cleans the code up. [...]
    > looks good, but i think you have removed an important optimization:
    > overlapping the issuing/finishing of read requests with copying memory, on
    > 1k filesystems. This should not matter much on bigger boxes, but on
    > smaller ones i've seen a definite advantage. So it's fine (and wanted) to

    Erm... I'm not sure that it's going to be a win - could you describe a
    scenario where we would write enough to make the copying sufficiently long
    _and_ would hit the need to wait on read request at the last block? IOW,
    what situation did you catch when testing old code? It _did_ wait on the
    first read request before copying anything, so if there was a difference
    it either came from waiting on the last one or from something completely

    > issue read requests first (the old version didnt do this), but you are
    > waiting for them to finish synchronously - this should be interleaved with
    > memory copies. Also there is a deadlock situation which David Miller
    > noticed some time ago (i think this is still present): just try read()-ing
    > a file into a freshly mmap()-ed memory area. (where the mmap-ed page is
    > the same as the read() page.) Legal combination, instant stuck process.

    Huh? generic_file_read() unlocks the page before calling actor() (and
    causing the page-in). What's the problem with it?

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