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Btrfs: avoid IO stalls behind congested devices in a multi-device FS
The btrfs IO submission threads try to service a bunch of devices with a small number of threads. They do a congestion check to try and avoid waiting on requests for a busy device. The checks make sure we've sent a few requests down to a given device just so that we aren't bouncing between busy devices without actually sending down any IO. The counter used to decide if we can switch to the next device is somewhat overloaded. It is also being used to decide if we've done a good batch of requests between the WRITE_SYNC or regular priority lists. It may get reset to zero often, leaving us hammering on a busy device instead of moving on to another disk. This commit adds a new counter for the number of bios sent while servicing a device. It doesn't get reset or fiddled with. On multi-device filesystems, this fixes IO stalls in streaming write workloads. Signed-off-by: Chris Mason <chris.mason@oracle.com>
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parent
d84275c938
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d644d8a1e3
1 changed files with 4 additions and 1 deletions
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@ -161,6 +161,7 @@ static noinline int run_scheduled_bios(struct btrfs_device *device)
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int again = 0;
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int again = 0;
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unsigned long num_run;
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unsigned long num_run;
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unsigned long num_sync_run;
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unsigned long num_sync_run;
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unsigned long batch_run = 0;
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unsigned long limit;
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unsigned long limit;
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unsigned long last_waited = 0;
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unsigned long last_waited = 0;
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int force_reg = 0;
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int force_reg = 0;
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@ -257,6 +258,8 @@ static noinline int run_scheduled_bios(struct btrfs_device *device)
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BUG_ON(atomic_read(&cur->bi_cnt) == 0);
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BUG_ON(atomic_read(&cur->bi_cnt) == 0);
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submit_bio(cur->bi_rw, cur);
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submit_bio(cur->bi_rw, cur);
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num_run++;
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num_run++;
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batch_run++;
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if (bio_sync(cur))
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if (bio_sync(cur))
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num_sync_run++;
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num_sync_run++;
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@ -273,7 +276,7 @@ static noinline int run_scheduled_bios(struct btrfs_device *device)
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* is now congested. Back off and let other work structs
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* is now congested. Back off and let other work structs
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* run instead
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* run instead
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*/
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*/
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if (pending && bdi_write_congested(bdi) && num_run > 16 &&
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if (pending && bdi_write_congested(bdi) && batch_run > 32 &&
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fs_info->fs_devices->open_devices > 1) {
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fs_info->fs_devices->open_devices > 1) {
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struct io_context *ioc;
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struct io_context *ioc;
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