[PATCH v8 13/14] mm: zswap: Allocate pool batching resources if the compressor supports batching.

Kanchana P Sridhar
2025-03-03T08:47:43Z

This patch adds support for the per-CPU acomp_ctx to track multiple
compression/decompression requests and multiple compression destination
buffers. The zswap_cpu_comp_prepare() CPU onlining code will get the
maximum batch-size the compressor supports. If so, it will allocate the
necessary batching resources.

However, zswap does not use more than one request yet. Follow-up patches
will actually utilize the multiple acomp_ctx requests/buffers for batch
compression/decompression of multiple pages.

The newly added ZSWAP_MAX_BATCH_SIZE limits the amount of extra memory used
for batching. There is a small extra memory overhead of allocating the
"reqs" and "buffers" arrays for compressors that do not support batching.

Signed-off-by: Kanchana P Sridhar <kanchana.p.sridhar@intel.com>
---
mm/zswap.c | 99 +++++++++++++++++++++++++++++++++++++-----------------
1 file changed, 69 insertions(+), 30 deletions(-)

diff --git a/mm/zswap.c b/mm/zswap.c
index cff96df1df8b..fae59d6d5147 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -78,6 +78,16 @@ static bool zswap_pool_reached_full;

#define ZSWAP_PARAM_UNSET ""

+/*
+ * For compression batching of large folios:
+ * Maximum number of acomp compress requests that will be processed
+ * in a batch, iff the zswap compressor supports batching.
+ * This limit exists because we preallocate enough requests and buffers
+ * in the per-cpu acomp_ctx accordingly. Hence, a higher limit means higher
+ * memory usage.
+ */
+#define ZSWAP_MAX_BATCH_SIZE 8U
+
static int zswap_setup(void);

/* Enable/disable zswap */
@@ -143,8 +153,8 @@ bool zswap_never_enabled(void)

struct crypto_acomp_ctx {
struct crypto_acomp *acomp;
- struct acomp_req *req;
- u8 *buffer;
+ struct acomp_req **reqs;
+ u8 **buffers;
u8 nr_reqs;
struct crypto_wait wait;
struct mutex mutex;
@@ -251,13 +261,22 @@ static void __zswap_pool_empty(struct percpu_ref *ref);
static void acomp_ctx_dealloc(struct crypto_acomp_ctx *acomp_ctx)
{
if (!IS_ERR_OR_NULL(acomp_ctx) && acomp_ctx->nr_reqs) {
+ u8 i;
+
+ if (acomp_ctx->reqs) {
+ for (i = 0; i < acomp_ctx->nr_reqs; ++i)
+ if (!IS_ERR_OR_NULL(acomp_ctx->reqs[i]))
+ acomp_request_free(acomp_ctx->reqs[i]);
+ kfree(acomp_ctx->reqs);
+ acomp_ctx->reqs = NULL;
+ }

- if (!IS_ERR_OR_NULL(acomp_ctx->req))
- acomp_request_free(acomp_ctx->req);
- acomp_ctx->req = NULL;
-
- kfree(acomp_ctx->buffer);
- acomp_ctx->buffer = NULL;
+ if (acomp_ctx->buffers) {
+ for (i = 0; i < acomp_ctx->nr_reqs; ++i)
+ kfree(acomp_ctx->buffers[i]);
+ kfree(acomp_ctx->buffers);
+ acomp_ctx->buffers = NULL;
+ }

if (!IS_ERR_OR_NULL(acomp_ctx->acomp))
crypto_free_acomp(acomp_ctx->acomp);
@@ -271,6 +290,7 @@ static int zswap_cpu_comp_prepare(unsigned int cpu, struct hlist_node *node)
struct zswap_pool *pool = hlist_entry(node, struct zswap_pool, node);
struct crypto_acomp_ctx *acomp_ctx = per_cpu_ptr(pool->acomp_ctx, cpu);
int ret = -ENOMEM;
+ u8 i;

/*
* Just to be even more fail-safe against changes in assumptions and/or
@@ -292,22 +312,41 @@ static int zswap_cpu_comp_prepare(unsigned int cpu, struct hlist_node *node)
goto fail;
}

- acomp_ctx->nr_reqs = 1;
+ acomp_ctx->nr_reqs = min(ZSWAP_MAX_BATCH_SIZE,
+ crypto_acomp_batch_size(acomp_ctx->acomp));

- acomp_ctx->req = acomp_request_alloc(acomp_ctx->acomp);
- if (!acomp_ctx->req) {
- pr_err("could not alloc crypto acomp_request %s\n",
- pool->tfm_name);
- ret = -ENOMEM;
+ acomp_ctx->reqs = kcalloc_node(acomp_ctx->nr_reqs, sizeof(struct acomp_req *),
+ GFP_KERNEL, cpu_to_node(cpu));
+ if (!acomp_ctx->reqs)
goto fail;
+
+ for (i = 0; i < acomp_ctx->nr_reqs; ++i) {
+ acomp_ctx->reqs[i] = acomp_request_alloc(acomp_ctx->acomp);
+ if (!acomp_ctx->reqs[i]) {
+ pr_err("could not alloc crypto acomp_request reqs[%d] %s\n",
+ i, pool->tfm_name);
+ goto fail;
+ }
}

- acomp_ctx->buffer = kmalloc_node(PAGE_SIZE * 2, GFP_KERNEL, cpu_to_node(cpu));
- if (!acomp_ctx->buffer) {
- ret = -ENOMEM;
+ acomp_ctx->buffers = kcalloc_node(acomp_ctx->nr_reqs, sizeof(u8 *),
+ GFP_KERNEL, cpu_to_node(cpu));
+ if (!acomp_ctx->buffers)
goto fail;
+
+ for (i = 0; i < acomp_ctx->nr_reqs; ++i) {
+ acomp_ctx->buffers[i] = kmalloc_node(PAGE_SIZE * 2, GFP_KERNEL,
+ cpu_to_node(cpu));
+ if (!acomp_ctx->buffers[i])
+ goto fail;
}

+ /*
+ * The crypto_wait is used only in fully synchronous, i.e., with scomp
+ * or non-poll mode of acomp, hence there is only one "wait" per
+ * acomp_ctx, with callback set to reqs[0], under the assumption that
+ * there is at least 1 request per acomp_ctx.
+ */
crypto_init_wait(&acomp_ctx->wait);

/*
@@ -315,7 +354,7 @@ static int zswap_cpu_comp_prepare(unsigned int cpu, struct hlist_node *node)
* crypto_wait_req(); if the backend of acomp is scomp, the callback
* won't be called, crypto_wait_req() will return without blocking.
*/
- acomp_request_set_callback(acomp_ctx->req, CRYPTO_TFM_REQ_MAY_BACKLOG,
+ acomp_request_set_callback(acomp_ctx->reqs[0], CRYPTO_TFM_REQ_MAY_BACKLOG,
crypto_req_done, &acomp_ctx->wait);

acomp_ctx->is_sleepable = acomp_is_async(acomp_ctx->acomp);
@@ -407,8 +446,8 @@ static struct zswap_pool *zswap_pool_create(char *type, char *compressor)
struct crypto_acomp_ctx *acomp_ctx = per_cpu_ptr(pool->acomp_ctx, cpu);

acomp_ctx->acomp = NULL;
- acomp_ctx->req = NULL;
- acomp_ctx->buffer = NULL;
+ acomp_ctx->reqs = NULL;
+ acomp_ctx->buffers = NULL;
acomp_ctx->__online = false;
acomp_ctx->nr_reqs = 0;
mutex_init(&acomp_ctx->mutex);
@@ -1026,7 +1065,7 @@ static bool zswap_compress(struct page *page, struct zswap_entry *entry,
u8 *dst;

acomp_ctx = acomp_ctx_get_cpu_lock(pool);
- dst = acomp_ctx->buffer;
+ dst = acomp_ctx->buffers[0];
sg_init_table(&input, 1);
sg_set_page(&input, page, PAGE_SIZE, 0);

@@ -1036,7 +1075,7 @@ static bool zswap_compress(struct page *page, struct zswap_entry *entry,
* giving the dst buffer with enough length to avoid buffer overflow.
*/
sg_init_one(&output, dst, PAGE_SIZE * 2);
- acomp_request_set_params(acomp_ctx->req, &input, &output, PAGE_SIZE, dlen);
+ acomp_request_set_params(acomp_ctx->reqs[0], &input, &output, PAGE_SIZE, dlen);

/*
* it maybe looks a little bit silly that we send an asynchronous request,
@@ -1050,8 +1089,8 @@ static bool zswap_compress(struct page *page, struct zswap_entry *entry,
* but in different threads running on different cpu, we have different
* acomp instance, so multiple threads can do (de)compression in parallel.
*/
- comp_ret = crypto_wait_req(crypto_acomp_compress(acomp_ctx->req), &acomp_ctx->wait);
- dlen = acomp_ctx->req->dlen;
+ comp_ret = crypto_wait_req(crypto_acomp_compress(acomp_ctx->reqs[0]), &acomp_ctx->wait);
+ dlen = acomp_ctx->reqs[0]->dlen;
if (comp_ret)
goto unlock;

@@ -1102,19 +1141,19 @@ static void zswap_decompress(struct zswap_entry *entry, struct folio *folio)
*/
if ((acomp_ctx->is_sleepable && !zpool_can_sleep_mapped(zpool)) ||
!virt_addr_valid(src)) {
- memcpy(acomp_ctx->buffer, src, entry->length);
- src = acomp_ctx->buffer;
+ memcpy(acomp_ctx->buffers[0], src, entry->length);
+ src = acomp_ctx->buffers[0];
zpool_unmap_handle(zpool, entry->handle);
}

sg_init_one(&input, src, entry->length);
sg_init_table(&output, 1);
sg_set_folio(&output, folio, PAGE_SIZE, 0);
- acomp_request_set_params(acomp_ctx->req, &input, &output, entry->length, PAGE_SIZE);
- BUG_ON(crypto_wait_req(crypto_acomp_decompress(acomp_ctx->req), &acomp_ctx->wait));
- BUG_ON(acomp_ctx->req->dlen != PAGE_SIZE);
+ acomp_request_set_params(acomp_ctx->reqs[0], &input, &output, entry->length, PAGE_SIZE);
+ BUG_ON(crypto_wait_req(crypto_acomp_decompress(acomp_ctx->reqs[0]), &acomp_ctx->wait));
+ BUG_ON(acomp_ctx->reqs[0]->dlen != PAGE_SIZE);

- if (src != acomp_ctx->buffer)
+ if (src != acomp_ctx->buffers[0])
zpool_unmap_handle(zpool, entry->handle);
acomp_ctx_put_unlock(acomp_ctx);
}
--
2.27.0