Messages in this thread | | | Date | Thu, 27 Apr 2006 16:39:23 +0200 | From | Jens Axboe <> | Subject | Re: [PATCH] likely cleanup: revert unlikely in ll_back_merge_fn |
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On Wed, Apr 26 2006, James Bottomley wrote: > On Wed, 2006-04-26 at 15:55 +0200, Jens Axboe wrote: > > On Wed, Apr 26 2006, James Bottomley wrote: > > > On Wed, 2006-04-26 at 07:20 +0200, Jens Axboe wrote: > > > > But blk_recount_segments() sets the BIO_SEG_VALID flag. Ugh ok > > > > __bio_add_page() basically kills the flag. James, I think you are the > > > > author of that addition, does it really need to be so restrictive? > > > > > > > > /* If we may be able to merge these biovecs, force a recount */ > > > > if (bio->bi_vcnt && (BIOVEC_PHYS_MERGEABLE(bvec-1, bvec) || > > > > BIOVEC_VIRT_MERGEABLE(bvec-1, bvec))) > > > > bio->bi_flags &= ~(1 << BIO_SEG_VALID); > > > > > > Help me out here ... I can't find this chunk of code in the current > > > tree. Where is it? > > > > Sorry, should have mentioned that. Current git tree (or 2.6.16 should be > > the same), fs/bio.c:__bio_add_page():401. > > OK, that's this change. > > http://www.kernel.org/git/?p=linux/kernel/git/tglx/history.git;a=commit;h=2fed84384a0b084d78252aa14d6bfae03deb268f > > I think the reason for this is that the bi_hw_back_size and bi_hw_front > size aren't updated without a segment recount, so you could get rid of > the valid flag clearing if you introduce a heuristic to update them.
Hmm yes, I'll ponder that a bit. Do you have any ideas on how to best handle that? I guess it's not a huge deal, would be nice to avoid the repeat segment calculations though.
-- Jens Axboe
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