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.
Cheers
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