md/r5cache: improve journal device efficiency

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It is important to be able to flush all stripes in raid5-cache.
Therefore, we need reserve some space on the journal device for
these flushes. If flush operation includes pending writes to the
stripe, we need to reserve (conf->raid_disk + 1) pages per stripe
for the flush out. This reduces the efficiency of journal space.
If we exclude these pending writes from flush operation, we only
need (conf->max_degraded + 1) pages per stripe.

With this patch, when log space is critical (R5C_LOG_CRITICAL=1),
pending writes will be excluded from stripe flush out. Therefore,
we can reduce reserved space for flush out and thus improve journal
device efficiency.

Signed-off-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Shaohua Li <shli@fb.com>

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Song Liu 2017-01-24 14:08:23 -08:00 • committed by Shaohua Li

parent 03b047f45c

commit 39b99586b3

2 changed files with 58 additions and 20 deletions

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36

drivers/md/raid5-cache.c

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42

drivers/md/raid5.c

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