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?
..
CC'ing Neil Brown.
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