Re: [PATCH] mm: zswap: multiple zpool support

Yosry Ahmed
2023-05-31T02:33:11Z

On Tue, May 30, 2023 at 7:29 PM Yosry Ahmed <yosryahmed@google.com> wrote:
>
> Support using multiple zpools of the same type in zswap, for concurrency
> purposes. Add CONFIG_ZSWAP_NR_ZPOOLS_ORDER to control the number of
> zpools. The order is specific by the config rather than the absolute
> number to guarantee a power of 2. This is useful so that we can use
> deterministically link each entry to a zpool by hashing the zswap_entry
> pointer.
>
> On a setup with zswap and zsmalloc, comparing a single zpool (current
> default) to 32 zpools (by setting CONFIG_ZSWAP_NR_ZPOOLS_ORDER=32) shows
> improvements in the zsmalloc lock contention, especially on the swap out
> path.
>
> The following shows the perf analysis of the swapout path when 10
> workloads are simulatenously reclaiming and refaulting tmpfs pages.
> There are some improvements on the swapin path as well, but much less
> significant.
>
> 1 zpool:
>
> |--28.99%--zswap_frontswap_store
> | |
> <snip>
> | |
> | |--8.98%--zpool_map_handle
> | | |
> | | --8.98%--zs_zpool_map
> | | |
> | | --8.95%--zs_map_object
> | | |
> | | --8.38%--_raw_spin_lock
> | | |
> | | --7.39%--queued_spin_lock_slowpath
> | |
> | |--8.82%--zpool_malloc
> | | |
> | | --8.82%--zs_zpool_malloc
> | | |
> | | --8.80%--zs_malloc
> | | |
> | | |--7.21%--_raw_spin_lock
> | | | |
> | | | --6.81%--queued_spin_lock_slowpath
> <snip>
>
> 32 zpools:
>
> |--16.73%--zswap_frontswap_store
> | |
> <snip>
> | |
> | |--1.81%--zpool_malloc
> | | |
> | | --1.81%--zs_zpool_malloc
> | | |
> | | --1.79%--zs_malloc
> | | |
> | | --0.73%--obj_malloc
> | |
> | |--1.06%--zswap_update_total_size
> | |
> | |--0.59%--zpool_map_handle
> | | |
> | | --0.59%--zs_zpool_map
> | | |
> | | --0.57%--zs_map_object
> | | |
> | | --0.51%--_raw_spin_lock
> <snip>
>
> Suggested-by: Yu Zhao <yuzhao@google.com>
> Signed-off-by: Yosry Ahmed <yosryahmed@google.com>
> ---
> mm/Kconfig | 12 +++++++
> mm/zswap.c | 95 ++++++++++++++++++++++++++++++++++++------------------
> 2 files changed, 76 insertions(+), 31 deletions(-)
>
> diff --git a/mm/Kconfig b/mm/Kconfig
> index 92c30879bf67..de1da56d2c07 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -59,6 +59,18 @@ config ZSWAP_EXCLUSIVE_LOADS
> The cost is that if the page was never dirtied and needs to be
> swapped out again, it will be re-compressed.
>
> +config ZSWAP_NR_ZPOOLS_ORDER
> + int "Number of zpools in zswap, as power of 2"
> + default 0
> + depends on ZSWAP
> + help
> + This options determines the number of zpools to use for zswap, it
> + will be 1 << CONFIG_ZSWAP_NR_ZPOOLS_ORDER.
> +
> + Having multiple zpools helps with concurrency and lock contention
> + on the swap in and swap out paths, but uses a little bit of extra
> + space.
> +
> choice
> prompt "Default compressor"
> depends on ZSWAP
> diff --git a/mm/zswap.c b/mm/zswap.c
> index fba80330afd1..7111036f8aa5 100644
> --- a/mm/zswap.c
> +++ b/mm/zswap.c
> @@ -137,6 +137,9 @@ static bool zswap_non_same_filled_pages_enabled = true;
> module_param_named(non_same_filled_pages_enabled, zswap_non_same_filled_pages_enabled,
> bool, 0644);
>
> +/* Order of zpools for global pool when memcg is enabled */

This comment is an artifact of an older implementation, please ignore.

> +static unsigned int zswap_nr_zpools = 1 << CONFIG_ZSWAP_NR_ZPOOLS_ORDER;
> +
> /*********************************
> * data structures
> **********************************/
> @@ -150,7 +153,6 @@ struct crypto_acomp_ctx {
> };
>
> struct zswap_pool {
> - struct zpool *zpool;
> struct crypto_acomp_ctx __percpu *acomp_ctx;
> struct kref kref;
> struct list_head list;
> @@ -158,6 +160,7 @@ struct zswap_pool {
> struct work_struct shrink_work;
> struct hlist_node node;
> char tfm_name[CRYPTO_MAX_ALG_NAME];
> + struct zpool *zpools[];
> };
>
> /*
> @@ -236,7 +239,7 @@ static bool zswap_has_pool;
>
> #define zswap_pool_debug(msg, p) \
> pr_debug("%s pool %s/%s\n", msg, (p)->tfm_name, \
> - zpool_get_type((p)->zpool))
> + zpool_get_type((p)->zpools[0]))
>
> static int zswap_writeback_entry(struct zpool *pool, unsigned long handle);
> static int zswap_pool_get(struct zswap_pool *pool);
> @@ -263,11 +266,13 @@ static void zswap_update_total_size(void)
> {
> struct zswap_pool *pool;
> u64 total = 0;
> + int i;
>
> rcu_read_lock();
>
> list_for_each_entry_rcu(pool, &zswap_pools, list)
> - total += zpool_get_total_size(pool->zpool);
> + for (i = 0; i < zswap_nr_zpools; i++)
> + total += zpool_get_total_size(pool->zpools[i]);
>
> rcu_read_unlock();
>
> @@ -350,6 +355,16 @@ static void zswap_rb_erase(struct rb_root *root, struct zswap_entry *entry)
> }
> }
>
> +static struct zpool *zswap_find_zpool(struct zswap_entry *entry)
> +{
> + int i;
> +
> + i = zswap_nr_zpools == 1 ? 0 :
> + hash_ptr(entry, ilog2(zswap_nr_zpools));
> +
> + return entry->pool->zpools[i];
> +}
> +
> /*
> * Carries out the common pattern of freeing and entry's zpool allocation,
> * freeing the entry itself, and decrementing the number of stored pages.
> @@ -363,7 +378,7 @@ static void zswap_free_entry(struct zswap_entry *entry)
> if (!entry->length)
> atomic_dec(&zswap_same_filled_pages);
> else {
> - zpool_free(entry->pool->zpool, entry->handle);
> + zpool_free(zswap_find_zpool(entry), entry->handle);
> zswap_pool_put(entry->pool);
> }
> zswap_entry_cache_free(entry);
> @@ -572,7 +587,8 @@ static struct zswap_pool *zswap_pool_find_get(char *type, char *compressor)
> list_for_each_entry_rcu(pool, &zswap_pools, list) {
> if (strcmp(pool->tfm_name, compressor))
> continue;
> - if (strcmp(zpool_get_type(pool->zpool), type))
> + /* all zpools share the same type */
> + if (strcmp(zpool_get_type(pool->zpools[0]), type))
> continue;
> /* if we can't get it, it's about to be destroyed */
> if (!zswap_pool_get(pool))
> @@ -587,14 +603,17 @@ static void shrink_worker(struct work_struct *w)
> {
> struct zswap_pool *pool = container_of(w, typeof(*pool),
> shrink_work);
> + int i;
>
> - if (zpool_shrink(pool->zpool, 1, NULL))
> - zswap_reject_reclaim_fail++;
> + for (i = 0; i < zswap_nr_zpools; i++)
> + if (zpool_shrink(pool->zpools[i], 1, NULL))
> + zswap_reject_reclaim_fail++;
> zswap_pool_put(pool);
> }
>
> static struct zswap_pool *zswap_pool_create(char *type, char *compressor)
> {
> + int i;
> struct zswap_pool *pool;
> char name[38]; /* 'zswap' + 32 char (max) num + \0 */
> gfp_t gfp = __GFP_NORETRY | __GFP_NOWARN | __GFP_KSWAPD_RECLAIM;
> @@ -611,19 +630,25 @@ static struct zswap_pool *zswap_pool_create(char *type, char *compressor)
> return NULL;
> }
>
> - pool = kzalloc(sizeof(*pool), GFP_KERNEL);
> + pool = kzalloc(sizeof(*pool) +
> + sizeof(pool->zpools[0]) * zswap_nr_zpools,
> + GFP_KERNEL);
> if (!pool)
> return NULL;
>
> - /* unique name for each pool specifically required by zsmalloc */
> - snprintf(name, 38, "zswap%x", atomic_inc_return(&zswap_pools_count));
> + for (i = 0; i < zswap_nr_zpools; i++) {
> + /* unique name for each pool specifically required by zsmalloc */
> + snprintf(name, 38, "zswap%x",
> + atomic_inc_return(&zswap_pools_count));
>
> - pool->zpool = zpool_create_pool(type, name, gfp, &zswap_zpool_ops);
> - if (!pool->zpool) {
> - pr_err("%s zpool not available\n", type);
> - goto error;
> + pool->zpools[i] = zpool_create_pool(type, name, gfp,
> + &zswap_zpool_ops);
> + if (!pool->zpools[i]) {
> + pr_err("%s zpool not available\n", type);
> + goto error;
> + }
> }
> - pr_debug("using %s zpool\n", zpool_get_type(pool->zpool));
> + pr_debug("using %s zpool\n", zpool_get_type(pool->zpools[0]));
>
> strscpy(pool->tfm_name, compressor, sizeof(pool->tfm_name));
>
> @@ -653,8 +678,8 @@ static struct zswap_pool *zswap_pool_create(char *type, char *compressor)
> error:
> if (pool->acomp_ctx)
> free_percpu(pool->acomp_ctx);
> - if (pool->zpool)
> - zpool_destroy_pool(pool->zpool);
> + while (i--)
> + zpool_destroy_pool(pool->zpools[i]);
> kfree(pool);
> return NULL;
> }
> @@ -703,11 +728,14 @@ static struct zswap_pool *__zswap_pool_create_fallback(void)
>
> static void zswap_pool_destroy(struct zswap_pool *pool)
> {
> + int i;
> +
> zswap_pool_debug("destroying", pool);
>
> cpuhp_state_remove_instance(CPUHP_MM_ZSWP_POOL_PREPARE, &pool->node);
> free_percpu(pool->acomp_ctx);
> - zpool_destroy_pool(pool->zpool);
> + for (i = 0; i < zswap_nr_zpools; i++)
> + zpool_destroy_pool(pool->zpools[i]);
> kfree(pool);
> }
>
> @@ -1160,6 +1188,7 @@ static int zswap_frontswap_store(unsigned type, pgoff_t offset,
> unsigned long handle, value;
> char *buf;
> u8 *src, *dst;
> + struct zpool *zpool;
> struct zswap_header zhdr = { .swpentry = swp_entry(type, offset) };
> gfp_t gfp;
>
> @@ -1259,11 +1288,13 @@ static int zswap_frontswap_store(unsigned type, pgoff_t offset,
> }
>
> /* store */
> - hlen = zpool_evictable(entry->pool->zpool) ? sizeof(zhdr) : 0;
> + zpool = zswap_find_zpool(entry);
> + hlen = zpool_evictable(zpool) ? sizeof(zhdr) : 0;
> gfp = __GFP_NORETRY | __GFP_NOWARN | __GFP_KSWAPD_RECLAIM;
> - if (zpool_malloc_support_movable(entry->pool->zpool))
> + if (zpool_malloc_support_movable(zpool))
> gfp |= __GFP_HIGHMEM | __GFP_MOVABLE;
> - ret = zpool_malloc(entry->pool->zpool, hlen + dlen, gfp, &handle);
> + ret = zpool_malloc(zpool, hlen + dlen, gfp, &handle);
> +
> if (ret == -ENOSPC) {
> zswap_reject_compress_poor++;
> goto put_dstmem;
> @@ -1272,10 +1303,10 @@ static int zswap_frontswap_store(unsigned type, pgoff_t offset,
> zswap_reject_alloc_fail++;
> goto put_dstmem;
> }
> - buf = zpool_map_handle(entry->pool->zpool, handle, ZPOOL_MM_WO);
> + buf = zpool_map_handle(zpool, handle, ZPOOL_MM_WO);
> memcpy(buf, &zhdr, hlen);
> memcpy(buf + hlen, dst, dlen);
> - zpool_unmap_handle(entry->pool->zpool, handle);
> + zpool_unmap_handle(zpool, handle);
> mutex_unlock(acomp_ctx->mutex);
>
> /* populate entry */
> @@ -1353,6 +1384,7 @@ static int zswap_frontswap_load(unsigned type, pgoff_t offset,
> u8 *src, *dst, *tmp;
> unsigned int dlen;
> int ret;
> + struct zpool *zpool;
>
> /* find */
> spin_lock(&tree->lock);
> @@ -1372,7 +1404,8 @@ static int zswap_frontswap_load(unsigned type, pgoff_t offset,
> goto stats;
> }
>
> - if (!zpool_can_sleep_mapped(entry->pool->zpool)) {
> + zpool = zswap_find_zpool(entry);
> + if (!zpool_can_sleep_mapped(zpool)) {
> tmp = kmalloc(entry->length, GFP_KERNEL);
> if (!tmp) {
> ret = -ENOMEM;
> @@ -1382,14 +1415,14 @@ static int zswap_frontswap_load(unsigned type, pgoff_t offset,
>
> /* decompress */
> dlen = PAGE_SIZE;
> - src = zpool_map_handle(entry->pool->zpool, entry->handle, ZPOOL_MM_RO);
> - if (zpool_evictable(entry->pool->zpool))
> + src = zpool_map_handle(zpool, entry->handle, ZPOOL_MM_RO);
> + if (zpool_evictable(zpool))
> src += sizeof(struct zswap_header);
>
> - if (!zpool_can_sleep_mapped(entry->pool->zpool)) {
> + if (!zpool_can_sleep_mapped(zpool)) {
> memcpy(tmp, src, entry->length);
> src = tmp;
> - zpool_unmap_handle(entry->pool->zpool, entry->handle);
> + zpool_unmap_handle(zpool, entry->handle);
> }
>
> acomp_ctx = raw_cpu_ptr(entry->pool->acomp_ctx);
> @@ -1401,8 +1434,8 @@ static int zswap_frontswap_load(unsigned type, pgoff_t offset,
> ret = crypto_wait_req(crypto_acomp_decompress(acomp_ctx->req), &acomp_ctx->wait);
> mutex_unlock(acomp_ctx->mutex);
>
> - if (zpool_can_sleep_mapped(entry->pool->zpool))
> - zpool_unmap_handle(entry->pool->zpool, entry->handle);
> + if (zpool_can_sleep_mapped(zpool))
> + zpool_unmap_handle(zpool, entry->handle);
> else
> kfree(tmp);
>
> @@ -1558,7 +1591,7 @@ static int zswap_setup(void)
> pool = __zswap_pool_create_fallback();
> if (pool) {
> pr_info("loaded using pool %s/%s\n", pool->tfm_name,
> - zpool_get_type(pool->zpool));
> + zpool_get_type(pool->zpools[0]));
> list_add(&pool->list, &zswap_pools);
> zswap_has_pool = true;
> } else {
> --
> 2.41.0.rc0.172.g3f132b7071-goog
>