Commit 84890c03 authored by Shaohua Li's avatar Shaohua Li
Browse files

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: default avatarShaohua Li <shli@fb.com>
parent 535ae4eb

drivers/md/raid5-cache.c

+3 −3
Original line number Diff line number Diff line
@@ -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

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