On 10/14/24 16:49, Meir Elisha wrote:
> Enlarging the hash table size can significantly improve transaction
> manager hash operations. This commit adds the tm_hash_table_size
> module_param that sets the hash size.
>
> For demonstration, I've created a thin volume, filled it with 4.8TiB of
> sequential data and took a snapshot. then, I overwritten the volume in a
> way that caused a maximum btree nodes to be allocated. I've repeated the
> process for 5 snapshots and measured the first snapshot deletion time.
>
> When using 128k hash size (instead of the 256 default value) I was able
> to reduce snapshot deletion time from 42min to 4min (10x improvement).
>
> Signed-off-by: Meir Elisha <meir.elisha@xxxxxxxxxxx>
> ---
>
> Script used for demonstration attached below.
>
> .../persistent-data/dm-transaction-manager.c | 51 ++++++++++++++++---
> 1 file changed, 43 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/md/persistent-data/dm-transaction-manager.c b/drivers/md/persistent-data/dm-transaction-manager.c
> index c7ba4e6cbbc7..8d486b1e6693 100644
> --- a/drivers/md/persistent-data/dm-transaction-manager.c
> +++ b/drivers/md/persistent-data/dm-transaction-manager.c
> @@ -10,6 +10,7 @@
> #include "dm-space-map-metadata.h"
> #include "dm-persistent-data-internal.h"
>
> +#include <linux/moduleparam.h>
> #include <linux/export.h>
> #include <linux/mutex.h>
> #include <linux/hash.h>
> @@ -84,8 +85,35 @@ struct shadow_info {
> /*
> * It would be nice if we scaled with the size of transaction.
> */
> -#define DM_HASH_SIZE 256
> -#define DM_HASH_MASK (DM_HASH_SIZE - 1)
> +static uint tm_hash_table_size = 256;
> +
> +static int param_set_hash_size(const char *val, const struct kernel_param *kp)
> +{
> + unsigned int num;
> + int ret;
> +
> + if (!val)
> + return -EINVAL;
> +
> + ret = kstrtouint(val, 0, &num);
> + if (ret)
> + return ret;
> +
> + /* Hash size must be a power of 2 */
> + if (!(num && !(num & (num - 1))))
> + return -EINVAL;
> +
> + *((unsigned int *)kp->arg) = num;
> + return 0;
> +}
> +
> +static const struct kernel_param_ops tm_hash_table_size_ops = {
> + .set = param_set_hash_size,
> + .get = param_get_uint
> +};
> +
> +module_param_cb(tm_hash_table_size, &tm_hash_table_size_ops, &tm_hash_table_size, 0644);
> +MODULE_PARM_DESC(tm_hash_table_size, "transaction manager hash size");
>
> struct dm_transaction_manager {
> int is_clone;
> @@ -95,8 +123,9 @@ struct dm_transaction_manager {
> struct dm_space_map *sm;
>
> spinlock_t lock;
> - struct hlist_head buckets[DM_HASH_SIZE];
> -
> + struct hlist_head *buckets;
> + uint hash_size;
> + uint hash_mask;
> struct prefetch_set prefetches;
> };
>
> @@ -105,7 +134,7 @@ struct dm_transaction_manager {
> static int is_shadow(struct dm_transaction_manager *tm, dm_block_t b)
> {
> int r = 0;
> - unsigned int bucket = dm_hash_block(b, DM_HASH_MASK);
> + unsigned int bucket = dm_hash_block(b, tm->hash_mask);
> struct shadow_info *si;
>
> spin_lock(&tm->lock);
> @@ -131,7 +160,7 @@ static void insert_shadow(struct dm_transaction_manager *tm, dm_block_t b)
> si = kmalloc(sizeof(*si), GFP_NOIO);
> if (si) {
> si->where = b;
> - bucket = dm_hash_block(b, DM_HASH_MASK);
> + bucket = dm_hash_block(b, tm->hash_mask);
> spin_lock(&tm->lock);
> hlist_add_head(&si->hlist, tm->buckets + bucket);
> spin_unlock(&tm->lock);
> @@ -146,7 +175,7 @@ static void wipe_shadow_table(struct dm_transaction_manager *tm)
> int i;
>
> spin_lock(&tm->lock);
> - for (i = 0; i < DM_HASH_SIZE; i++) {
> + for (i = 0; i < tm->hash_size; i++) {
> bucket = tm->buckets + i;
> hlist_for_each_entry_safe(si, tmp, bucket, hlist)
> kfree(si);
> @@ -169,13 +198,19 @@ static struct dm_transaction_manager *dm_tm_create(struct dm_block_manager *bm,
> if (!tm)
> return ERR_PTR(-ENOMEM);
>
> + tm->hash_size = tm_hash_table_size;
> + tm->buckets = kmalloc_array(tm->hash_size, sizeof(*tm->buckets), GFP_KERNEL);
> + if (!tm->buckets)
> + return ERR_PTR(-ENOMEM);
> +
> tm->is_clone = 0;
> tm->real = NULL;
> tm->bm = bm;
> tm->sm = sm;
> + tm->hash_mask = tm->hash_size - 1;
>
> spin_lock_init(&tm->lock);
> - for (i = 0; i < DM_HASH_SIZE; i++)
> + for (i = 0; i < tm->hash_size; i++)
> INIT_HLIST_HEAD(tm->buckets + i);
>
> prefetch_init(&tm->prefetches);
Hi all,
I wanted to follow up on this patch.
Could you please review it when you have a chance?
If you need any additional information or have concerns, let me know.
Thanks for your time.
