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md/raid5-cache: bump flush stripe batch size 

Bump the flush stripe batch size to 2048. For my 12 disks raid
array, the stripes takes:
12 * 4k * 2048 = 96MB

This is still quite small. A hardware raid card generally has 1GB size,
which we suggest the raid5-cache has similar cache size.

The advantage of a big batch size is we can dispatch a lot of IO in the
same time, then we can do some scheduling to make better IO pattern.

Last patch prioritizes stripes, so we don't worry about a big flush
stripe batch will starve normal stripes.

Signed-off-by: Shaohua Li <shli@fb.com>
This commit is contained in:
Shaohua Li 2017-02-15 19:58:05 -08:00
parent 535ae4eb12
commit 84890c03b6
1 changed files with 3 additions and 3 deletions
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6
drivers/md/raid5-cache.c
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@ -43,7 +43,7 @@
/* wake up reclaim thread periodically */
#define R5C_RECLAIM_WAKEUP_INTERVAL (30 * HZ)
/* start flush with these full stripes */
#define R5C_FULL_STRIPE_FLUSH_BATCH 256
#define R5C_FULL_STRIPE_FLUSH_BATCH(conf) (conf->max_nr_stripes / 4)
/* reclaim stripes in groups */
#define R5C_RECLAIM_STRIPE_GROUP (NR_STRIPE_HASH_LOCKS * 2)
@ -381,7 +381,7 @@ void r5c_check_cached_full_stripe(struct r5conf *conf)
* or a full stripe (chunk size / 4k stripes).
*/
if (atomic_read(&conf->r5c_cached_full_stripes) >=
min(R5C_FULL_STRIPE_FLUSH_BATCH,
min(R5C_FULL_STRIPE_FLUSH_BATCH(conf),
conf->chunk_sectors >> STRIPE_SHIFT))
r5l_wake_reclaim(conf->log, 0);
}
@ -1393,7 +1393,7 @@ static void r5c_do_reclaim(struct r5conf *conf)
stripes_to_flush = R5C_RECLAIM_STRIPE_GROUP;
else if (total_cached > conf->min_nr_stripes * 1 / 2 ||
atomic_read(&conf->r5c_cached_full_stripes) - flushing_full >
R5C_FULL_STRIPE_FLUSH_BATCH)
R5C_FULL_STRIPE_FLUSH_BATCH(conf))
/*
* if stripe cache pressure moderate, or if there is many full
* stripes,flush all full stripes