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authorShaohua Li <shli@kernel.org>2012-07-19 16:01:31 +1000
committerNeilBrown <neilb@suse.de>2012-07-19 16:01:31 +1000
commitb17459c05000fdbe8d10946570a26510f86ec0f6 (patch)
tree251a9e640d91a9b9ffc804519ea07ed365035636 /drivers/md/raid5.h
parent7eaf7e8eb31747e4259d60288b44b194fb3d56c7 (diff)
downloadtalos-op-linux-b17459c05000fdbe8d10946570a26510f86ec0f6.tar.gz
talos-op-linux-b17459c05000fdbe8d10946570a26510f86ec0f6.zip
raid5: add a per-stripe lock
Add a per-stripe lock to protect stripe specific data. The purpose is to reduce lock contention of conf->device_lock. stripe ->toread, ->towrite are protected by per-stripe lock. Accessing bio list of the stripe is always serialized by this lock, so adding bio to the lists (add_stripe_bio()) and removing bio from the lists (like ops_run_biofill()) not race. If bio in ->read, ->written ... list are not shared by multiple stripes, we don't need any lock to protect ->read, ->written, because STRIPE_ACTIVE will protect them. If the bio are shared, there are two protections: 1. bi_phys_segments acts as a reference count 2. traverse the list uses r5_next_bio, which makes traverse never access bio not belonging to the stripe Let's have an example: | stripe1 | stripe2 | stripe3 | ...bio1......|bio2|bio3|....bio4..... stripe2 has 4 bios, when it's finished, it will decrement bi_phys_segments for all bios, but only end_bio for bio2 and bio3. bio1->bi_next still points to bio2, but this doesn't matter. When stripe1 is finished, it will not touch bio2 because of r5_next_bio check. Next time stripe1 will end_bio for bio1 and stripe3 will end_bio bio4. before add_stripe_bio() addes a bio to a stripe, we already increament the bio bi_phys_segments, so don't worry other stripes release the bio. Signed-off-by: Shaohua Li <shli@fusionio.com> Signed-off-by: NeilBrown <neilb@suse.de>
Diffstat (limited to 'drivers/md/raid5.h')
-rw-r--r--drivers/md/raid5.h1
1 files changed, 1 insertions, 0 deletions
diff --git a/drivers/md/raid5.h b/drivers/md/raid5.h
index 2164021f3b5f..f03fb3395183 100644
--- a/drivers/md/raid5.h
+++ b/drivers/md/raid5.h
@@ -210,6 +210,7 @@ struct stripe_head {
int disks; /* disks in stripe */
enum check_states check_state;
enum reconstruct_states reconstruct_state;
+ spinlock_t stripe_lock;
/**
* struct stripe_operations
* @target - STRIPE_OP_COMPUTE_BLK target
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