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    SubjectRe: QUEUE_FLAG_CLUSTER: not working in 2.6.24 ?
    On Thu, Dec 13 2007, Mark Lord wrote:
    > Mark Lord wrote:
    > >Jens Axboe wrote:
    > >>On Thu, Dec 13 2007, Mark Lord wrote:
    > >>>Matthew Wilcox wrote:
    > >>>>On Thu, Dec 13, 2007 at 01:48:18PM -0500, Mark Lord wrote:
    > >>>>>Problem confirmed. 2.6.23.8 regularly generates segments up to
    > >>>>>64KB for libata,
    > >>>>>but 2.6.24 uses only 4KB segments and a *few* 8KB segments.
    > >>>>Just a suspicion ... could this be slab vs slub? ie check your configs
    > >>>>are the same / similar between the two kernels.
    > >>>..
    > >>>
    > >>>Mmmm.. a good thought, that one.
    > >>>But I just rechecked, and both have CONFIG_SLAB=y
    > >>>
    > >>>My guess is that something got changed around when Jens
    > >>>reworked the block layer for 2.6.24.
    > >>>I'm going to dig around in there now.
    > >>
    > >>I didn't rework the block layer for 2.6.24 :-). The core block layer
    > >>changes since 2.6.23 are:
    > >>
    > >>- Support for empty barriers. Not a likely candidate.
    > >>- Shared tag queue fixes. Totally unlikely.
    > >>- sg chaining support. Not likely.
    > >>- The bio changes from Neil. Of the bunch, the most likely suspects in
    > >> this area, since it changes some of the code involved with merges and
    > >> blk_rq_map_sg().
    > >>- Lots of simple stuff, again very unlikely.
    > >>
    > >>Anyway, it sounds odd for this to be a block layer problem if you do see
    > >>occasional segments being merged. So it sounds more like the input data
    > >>having changed.
    > >>
    > >>Why not just bisect it?
    > >..
    > >
    > >Because the early 2.6.24 series failed to boot on this machine
    > >due to bugs in the block layer -- so the code that caused this regression
    > >is probably in the stuff from before the kernels became usable here.
    > ..
    >
    > That sounds more harsh than intended --> the earlier 2.6.24 kernels (up to
    > the first couple of -rc* ones failed here because of incompatibilities
    > between the block/bio changes and libata.
    >
    > That's better, I think!

    No worries, I didn't pick it up as harsh just as an odd conclusion :-)

    If I were you, I'd just start from the first -rc that booted for you. If
    THAT has the bug, then we'll think of something else. If you don't get
    anywhere, I can run some tests tomorrow and see if I can reproduce it
    here.

    --
    Jens Axboe



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