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NeilBrown fd16f2e848 md/raid10: stop using bi_phys_segments
raid10 currently repurposes bi_phys_segments on each
incoming bio to count how many r10bio was used to encode the
request.

We need to know when the number of attached r10bio reaches
zero to:
1/ call bio_endio() when all IO on the bio is finished
2/ decrement ->nr_pending so that resync IO can proceed.

Now that the bio has its own __bi_remaining counter, that
can be used instead. We can call bio_inc_remaining to
increment the counter and call bio_endio() every time an
r10bio completes, rather than only when bi_phys_segments
reaches zero.

This addresses point 1, but not point 2.  bio_endio()
doesn't (and cannot) report when the last r10bio has
finished, so a different approach is needed.

So: instead of counting bios in ->nr_pending, count r10bios.
i.e. every time we attach a bio, increment nr_pending.
Every time an r10bio completes, decrement nr_pending.

Normally we only increment nr_pending after first checking
that ->barrier is zero, or some other non-trivial tests and
possible waiting.  When attaching multiple r10bios to a bio,
we only need the tests and the waiting once.  After the
first increment, subsequent increments can happen
unconditionally as they are really all part of the one
request.

So introduce inc_pending() which can be used when we know
that nr_pending is already elevated.

Note that this fixes a bug.  freeze_array() contains the line
	atomic_read(&conf->nr_pending) == conf->nr_queued+extra,
which implies that the units for ->nr_pending, ->nr_queued and extra
are the same.
->nr_queue and extra count r10_bios, but prior to this patch,
->nr_pending counted bios.  If a bio ever resulted in multiple
r10_bios (due to bad blocks), freeze_array() would not work correctly.
Now it does.

Signed-off-by: NeilBrown <neilb@suse.com>
Signed-off-by: Shaohua Li <shli@fb.com>
2017-03-22 19:17:41 -07:00
arch arm64 fixes/cleanups: 2017-03-16 11:47:28 -07:00
block blk-mq-sched: don't run the queue async from blk_mq_try_issue_directly() 2017-03-14 11:51:59 -06:00
certs
crypto
Documentation md: add sysfs entries for PPL 2017-03-16 16:55:55 -07:00
drivers md/raid10: stop using bi_phys_segments 2017-03-22 19:17:41 -07:00
firmware
fs Changes since last time: 2017-03-16 12:30:43 -07:00
include raid5-ppl: Partial Parity Log write logging implementation 2017-03-16 16:55:54 -07:00
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kernel Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2017-03-14 21:31:23 -07:00
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mm Merge branch 'for-4.11-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/percpu 2017-03-14 14:48:50 -07:00
net Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2017-03-14 21:31:23 -07:00
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tools Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2017-03-14 21:31:23 -07:00
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Linux kernel
============

This file was moved to Documentation/admin-guide/README.rst

Please notice that there are several guides for kernel developers and users.
These guides can be rendered in a number of formats, like HTML and PDF.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.