On 2015-12-20 23:44, Kent Overstreet wrote:
On Sun, Dec 20, 2015 at 07:18:01PM +0100, Christoph Hellwig wrote:
On Sun, Dec 20, 2015 at 09:51:14AM -0800, Linus Torvalds wrote:
> Kent, Jens, Christoph et al,
ie please see this bugzilla:
>o
> httpps://bugzilla.kernel.org/show_bug.cgi?id=109661
>
> where Artem Tashkinov bisected his problems with 4.3 down to commit
> b54ffb73cadc ("block: remove bio_get_nr_vecs()") that you've all
> signed off on.
Artem,
can you re-check the commits around this series again? I would be
extremtly surprised if it's really this particular commit and not
one just before it causing the problem - it just allocates bios
to the biggest possible instead of only allocating up to what
bio_add_page would accept.
pretty sure it's something with how blk_bio_segment_split() decides
what
segments are mergable and not. bio_get_nr_vecs() was just returning
nr_pages ==
queue_max_segments (ignoring sectors for the moment) - so wait, wtf?
that's
basically assuming no segment merging can ever happen, if it does then
this was
causing us to send smaller requests to the device than we could have
been.
so actually two possibilities I can see:
- in blk_bio_segment_split(), something's screwed up with how it
decides what
segments are going to be mergable or not. but I don't think that's
likely
since it's doing the exact same thing the rest of the segment
merging code
does.
- or, the driver was lying in its queue limits, using
queue_max_segments for
"the maximum number of pages I can possibly take", and that bug
lurked
undiscovered because of the screwed-upness in bio_get_nr_vecs().
Offhand I don't know where to start digging in the driver code to look
into the
second theory though. Tejun, you got any ideas?
Here's an actual bisect log which Linus was missing:
git bisect start
# bad: [6a13feb9c82803e2b815eca72fa7a9f5561d7861] Linux 4.3
git bisect bad 6a13feb9c82803e2b815eca72fa7a9f5561d7861
# good: [64291f7db5bd8150a74ad2036f1037e6a0428df2] Linux 4.2
git bisect good 64291f7db5bd8150a74ad2036f1037e6a0428df2
# bad: [807249d3ada1ff28a47c4054ca4edd479421b671] Merge branch
'upstream' of git://git.linux-mips.org/pub/scm/ralf/upstream-linus
git bisect bad 807249d3ada1ff28a47c4054ca4edd479421b671
# good: [102178108e2246cb4b329d3fb7872cd3d7120205] Merge tag
'armsoc-drivers' of
git://git.kernel.org/pub/scm/linux/kernel/git/arm/arm-soc
git bisect good 102178108e2246cb4b329d3fb7872cd3d7120205
# good: [62da98656b62a5ca57f22263705175af8ded5aa1] netfilter:
nf_conntrack: make nf_ct_zone_dflt built-in
git bisect good 62da98656b62a5ca57f22263705175af8ded5aa1
# good: [f1a3c0b933e7ff856223d6fcd7456d403e54e4e5] Merge tag
'devicetree-for-4.3' of
git://git.kernel.org/pub/scm/linux/kernel/git/robh/linux
git bisect good f1a3c0b933e7ff856223d6fcd7456d403e54e4e5
# bad: [9cbf22b37ae0592dea809cb8d424990774c21786] Merge tag 'dlm-4.3' of
git://git.kernel.org/pub/scm/linux/kernel/git/teigland/linux-dlm
git bisect bad 9cbf22b37ae0592dea809cb8d424990774c21786
# good: [8bdc69b764013a9b5ebeef7df8f314f1066c5d79] Merge branch
'for-4.3' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup
git bisect good 8bdc69b764013a9b5ebeef7df8f314f1066c5d79
# good: [df910390e2db07a76c87f258475f6c96253cee6c] Merge tag 'scsi-misc'
of git://git.kernel.org/pub/scm/linux/kernel/git/jejb/scsi
git bisect good df910390e2db07a76c87f258475f6c96253cee6c
# bad: [d975f309a8b250e67b66eabeb56be6989c783629] Merge branch
'for-4.3/sg' of git://git.kernel.dk/linux-block
git bisect bad d975f309a8b250e67b66eabeb56be6989c783629
# bad: [89e2a8404e4415da1edbac6ca4f7332b4a74fae2] crypto/omap-sham:
remove an open coded access to ->page_link
git bisect bad 89e2a8404e4415da1edbac6ca4f7332b4a74fae2
# good: [0e28997ec476bad4c7dbe0a08775290051325f53] btrfs: remove bio
splitting and merge_bvec_fn() calls
git bisect good 0e28997ec476bad4c7dbe0a08775290051325f53
# bad: [2ec3182f9c20a9eef0dacc0512cf2ca2df7be5ad] Documentation: update
notes in biovecs about arbitrarily sized bios
git bisect bad 2ec3182f9c20a9eef0dacc0512cf2ca2df7be5ad
# good: [7140aafce2fc14c5af02fdb7859b6bea0108be3d] md/raid5: get rid of
bio_fits_rdev()
git bisect good 7140aafce2fc14c5af02fdb7859b6bea0108be3d
# good: [6cf66b4caf9c71f64a5486cadbd71ab58d0d4307] fs: use helper
bio_add_page() instead of open coding on bi_io_vec
git bisect good 6cf66b4caf9c71f64a5486cadbd71ab58d0d4307
# bad: [b54ffb73cadcdcff9cc1ae0e11f502407e3e2e4c] block: remove
bio_get_nr_vecs()
git bisect bad b54ffb73cadcdcff9cc1ae0e11f502407e3e2e4c
And like he said since the step before the last one was good and the
very last one was bad there was no way I could have made a mistake.
--
To unsubscribe from this list: send the line "unsubscribe linux-ide" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
