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authorNeilBrown <neilb@suse.de>2014-05-28 05:39:22 +0200
committerNeilBrown <neilb@suse.de>2014-05-29 08:59:46 +0200
commit67f455486d2ea20b2d94d6adf5b9b783d079e321 (patch)
tree320f360d77b56f03c754b29fa617d61d25d40ec4 /drivers/md/dm-zero.c
parentmd: refuse to change shape of array if it is active but read-only (diff)
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md/raid56: Don't perform reads to support writes until stripe is ready.
If it is found that we need to pre-read some blocks before a write can succeed, we normally set STRIPE_DELAYED and don't actually perform the read until STRIPE_PREREAD_ACTIVE subsequently gets set. However for a degraded RAID6 we currently perform the reads as soon as we see that a write is pending. This significantly hurts throughput. So: - when handle_stripe_dirtying find a block that it wants on a device that is failed, set STRIPE_DELAY, instead of doing nothing, and - when fetch_block detects that a read might be required to satisfy a write, only perform the read if STRIPE_PREREAD_ACTIVE is set, and if we would actually need to read something to complete the write. This also helps RAID5, though less often as RAID5 supports a read-modify-write cycle. For RAID5 the read is performed too early only if the write is not a full 4K aligned write (i.e. no an R5_OVERWRITE). Also clean up a couple of horrible bits of formatting. Reported-by: Patrik HornĂ­k <patrik@dsl.sk> Signed-off-by: NeilBrown <neilb@suse.de>
Diffstat (limited to 'drivers/md/dm-zero.c')
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