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dm: add dm_num_hash_locks()

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Simple helper to use when DM core code needs to appropriately size,
based on num_online_cpus(), its data structures that split locks.

dm_num_hash_locks() rounds up num_online_cpus() to next power of 2
but caps return at DM_HASH_LOCKS_MAX (64).

This heuristic may evolve as warranted, but as-is it will serve as a
more informed basis for sizing the sharded lock structs in dm-bufio's
dm_buffer_cache (buffer_trees) and dm-bio-prison-v1's dm_bio_prison
(prison_regions).

Signed-off-by: Mike Snitzer <snitzer@kernel.org>
This commit is contained in:
Mike Snitzer 2023-03-27 13:59:25 -04:00
parent 3f8d3f5432
commit 0bac3f2f28
1 changed files with 10 additions and 0 deletions
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10
drivers/md/dm.h
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@ -20,6 +20,7 @@
#include <linux/completion.h>
#include <linux/kobject.h>
#include <linux/refcount.h>
#include <linux/log2.h>
#include "dm-stats.h"
@ -228,4 +229,13 @@ void dm_free_md_mempools(struct dm_md_mempools *pools);
*/
unsigned int dm_get_reserved_bio_based_ios(void);
#define DM_HASH_LOCKS_MAX 64
static inline unsigned int dm_num_hash_locks(void)
{
unsigned int num_locks = roundup_pow_of_two(num_online_cpus());
return min_t(unsigned int, num_locks, DM_HASH_LOCKS_MAX);
}
#endif