On Thu, Jul 31, 2025 at 9:36 PM Kanchana P Sridhar <kanchana.p.sridhar@xxxxxxxxx> wrote: > > This patch sets up zswap for allocating per-CPU resources optimally for > non-batching and batching compressors. > > A new ZSWAP_MAX_BATCH_SIZE constant is defined as 8U, to set an upper > limit on the number of pages in large folios that will be batch > compressed. > > As per Herbert's comments in [2] in response to the > crypto_acomp_batch_compress() and crypto_acomp_batch_decompress() API > proposed in [1], this series does not create new crypto_acomp batching > API. Instead, zswap compression batching uses the existing > crypto_acomp_compress() API in combination with the "void *kernel_data" > member added to "struct acomp_req" earlier in this series. > > It is up to the compressor to manage multiple requests, as needed, to > accomplish batch parallelism. zswap only needs to allocate the per-CPU > dst buffers according to the batch size supported by the compressor. > > A "u8 compr_batch_size" member is added to "struct zswap_pool", as per > Yosry's suggestion. pool->compr_batch_size is set as the minimum of the > compressor's max batch-size and ZSWAP_MAX_BATCH_SIZE. Accordingly, it > proceeds to allocate the necessary compression dst buffers in the > per-CPU acomp_ctx. > > Another "u8 batch_size" member is added to "struct zswap_pool" to store > the unit for batching large folio stores: for batching compressors, this > is the pool->compr_batch_size. For non-batching compressors, this is > ZSWAP_MAX_BATCH_SIZE. > > zswap does not use more than one dst buffer yet. Follow-up patches will > actually utilize the multiple acomp_ctx buffers for batch > compression/decompression of multiple pages. > > Thus, ZSWAP_MAX_BATCH_SIZE limits the amount of extra memory used for > batching. There is a small extra memory overhead of allocating > the acomp_ctx->buffers array for compressors that do not support > batching: On x86_64, the overhead is 1 pointer per-CPU (i.e. 8 bytes). > > [1]: https://patchwork.kernel.org/project/linux-mm/patch/20250508194134.28392-11-kanchana.p.sridhar@xxxxxxxxx/ > [2]: https://patchwork.kernel.org/comment/26382610 > > Signed-off-by: Kanchana P Sridhar <kanchana.p.sridhar@xxxxxxxxx> Mostly LGTM. Just a couple of questions below: > --- > mm/zswap.c | 82 +++++++++++++++++++++++++++++++++++++++++------------- > 1 file changed, 63 insertions(+), 19 deletions(-) > > diff --git a/mm/zswap.c b/mm/zswap.c > index efd501a7fe294..63a997b999537 100644 > --- a/mm/zswap.c > +++ b/mm/zswap.c > @@ -80,6 +80,9 @@ static bool zswap_pool_reached_full; > > #define ZSWAP_PARAM_UNSET "" > > +/* Limit the batch size to limit per-CPU memory usage for dst buffers. */ > +#define ZSWAP_MAX_BATCH_SIZE 8U > + > static int zswap_setup(void); > > /* Enable/disable zswap */ > @@ -147,7 +150,7 @@ struct crypto_acomp_ctx { > struct crypto_acomp *acomp; > struct acomp_req *req; > struct crypto_wait wait; > - u8 *buffer; > + u8 **buffers; > struct mutex mutex; > bool is_sleepable; > }; > @@ -166,6 +169,8 @@ struct zswap_pool { > struct work_struct release_work; > struct hlist_node node; > char tfm_name[CRYPTO_MAX_ALG_NAME]; > + u8 compr_batch_size; > + u8 batch_size; Apologies if this is explained elsewhere, but I'm very confused - why do we need both of these two fields? Seems like batch_size is defined below, and never changed: pool->batch_size = (pool->compr_batch_size > 1) ? pool->compr_batch_size : ZSWAP_MAX_BATCH_SIZE; Can we just determine this in zswap_store() as a local variable? > }; > > /* Global LRU lists shared by all zswap pools. */ > @@ -258,8 +263,10 @@ static void __zswap_pool_empty(struct percpu_ref *ref); > * zswap_cpu_comp_prepare(), not others. > * - Cleanup acomp_ctx resources on all cores in zswap_pool_destroy(). > */ > -static void acomp_ctx_dealloc(struct crypto_acomp_ctx *acomp_ctx) > +static void acomp_ctx_dealloc(struct crypto_acomp_ctx *acomp_ctx, u8 nr_buffers) > { > + u8 i; > + > if (IS_ERR_OR_NULL(acomp_ctx)) > return; > > @@ -269,7 +276,11 @@ static void acomp_ctx_dealloc(struct crypto_acomp_ctx *acomp_ctx) > if (!IS_ERR_OR_NULL(acomp_ctx->acomp)) > crypto_free_acomp(acomp_ctx->acomp); > > - kfree(acomp_ctx->buffer); > + if (acomp_ctx->buffers) { > + for (i = 0; i < nr_buffers; ++i) > + kfree(acomp_ctx->buffers[i]); > + kfree(acomp_ctx->buffers); > + } > } > > static struct zswap_pool *zswap_pool_create(char *type, char *compressor) > @@ -290,6 +301,7 @@ static struct zswap_pool *zswap_pool_create(char *type, char *compressor) > return NULL; > } > > + /* Many things rely on the zero-initialization. */ > pool = kzalloc(sizeof(*pool), GFP_KERNEL); > if (!pool) > return NULL; > @@ -352,13 +364,28 @@ static struct zswap_pool *zswap_pool_create(char *type, char *compressor) > goto ref_fail; > INIT_LIST_HEAD(&pool->list); > > + /* > + * Set the unit of compress batching for large folios, for quick > + * retrieval in the zswap_compress() fast path: > + * If the compressor is sequential (@pool->compr_batch_size is 1), > + * large folios will be compressed in batches of ZSWAP_MAX_BATCH_SIZE > + * pages, where each page in the batch is compressed sequentially. > + * We see better performance by processing the folio in batches of > + * ZSWAP_MAX_BATCH_SIZE, due to cache locality of working set > + * structures. > + */ > + pool->batch_size = (pool->compr_batch_size > 1) ? > + pool->compr_batch_size : ZSWAP_MAX_BATCH_SIZE; > + > zswap_pool_debug("created", pool); > > return pool; > > ref_fail: > for_each_possible_cpu(cpu) > - acomp_ctx_dealloc(per_cpu_ptr(pool->acomp_ctx, cpu)); > + acomp_ctx_dealloc(per_cpu_ptr(pool->acomp_ctx, cpu), > + pool->compr_batch_size); > + > error: > if (pool->acomp_ctx) > free_percpu(pool->acomp_ctx); > @@ -417,7 +444,8 @@ static void zswap_pool_destroy(struct zswap_pool *pool) > zswap_pool_debug("destroying", pool); > > for_each_possible_cpu(cpu) > - acomp_ctx_dealloc(per_cpu_ptr(pool->acomp_ctx, cpu)); > + acomp_ctx_dealloc(per_cpu_ptr(pool->acomp_ctx, cpu), > + pool->compr_batch_size); > > free_percpu(pool->acomp_ctx); > > @@ -876,6 +904,7 @@ 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; > > /* > * The per-CPU pool->acomp_ctx is zero-initialized on allocation. > @@ -888,10 +917,6 @@ static int zswap_cpu_comp_prepare(unsigned int cpu, struct hlist_node *node) > if (!IS_ERR_OR_NULL(acomp_ctx->acomp)) > return 0; > > - acomp_ctx->buffer = kmalloc_node(PAGE_SIZE * 2, GFP_KERNEL, cpu_to_node(cpu)); > - if (!acomp_ctx->buffer) > - return ret; > - > acomp_ctx->acomp = crypto_alloc_acomp_node(pool->tfm_name, 0, 0, cpu_to_node(cpu)); > if (IS_ERR_OR_NULL(acomp_ctx->acomp)) { > pr_err("could not alloc crypto acomp %s : %ld\n", > @@ -904,17 +929,36 @@ static int zswap_cpu_comp_prepare(unsigned int cpu, struct hlist_node *node) > acomp_ctx->req = acomp_request_alloc(acomp_ctx->acomp); > if (IS_ERR_OR_NULL(acomp_ctx->req)) { > pr_err("could not alloc crypto acomp_request %s\n", > - pool->tfm_name); > + pool->tfm_name); Is this intentional? :) > goto fail; > } > > - crypto_init_wait(&acomp_ctx->wait); > + /* > + * Allocate up to ZSWAP_MAX_BATCH_SIZE dst buffers if the > + * compressor supports batching. > + */ > + pool->compr_batch_size = min(ZSWAP_MAX_BATCH_SIZE, > + crypto_acomp_batch_size(acomp_ctx->acomp)); > + > + acomp_ctx->buffers = kcalloc_node(pool->compr_batch_size, sizeof(u8 *), > + GFP_KERNEL, cpu_to_node(cpu)); > + if (!acomp_ctx->buffers) > + goto fail; > + > + for (i = 0; i < pool->compr_batch_size; ++i) { > + acomp_ctx->buffers[i] = kmalloc_node(PAGE_SIZE * 2, GFP_KERNEL, > + cpu_to_node(cpu)); > + if (!acomp_ctx->buffers[i]) > + goto fail; > + } > > /* > * if the backend of acomp is async zip, crypto_req_done() will wakeup > * crypto_wait_req(); if the backend of acomp is scomp, the callback > * won't be called, crypto_wait_req() will return without blocking. > */ > + crypto_init_wait(&acomp_ctx->wait); > + > acomp_request_set_callback(acomp_ctx->req, CRYPTO_TFM_REQ_MAY_BACKLOG, > crypto_req_done, &acomp_ctx->wait); > > @@ -922,7 +966,7 @@ static int zswap_cpu_comp_prepare(unsigned int cpu, struct hlist_node *node) > return 0; > > fail: > - acomp_ctx_dealloc(acomp_ctx); > + acomp_ctx_dealloc(acomp_ctx, pool->compr_batch_size); > return ret; > } > > @@ -942,7 +986,7 @@ static bool zswap_compress(struct page *page, struct zswap_entry *entry, > > mutex_lock(&acomp_ctx->mutex); > > - dst = acomp_ctx->buffer; > + dst = acomp_ctx->buffers[0]; > sg_init_table(&input, 1); > sg_set_page(&input, page, PAGE_SIZE, 0); > > @@ -1003,19 +1047,19 @@ static bool zswap_decompress(struct zswap_entry *entry, struct folio *folio) > > acomp_ctx = raw_cpu_ptr(entry->pool->acomp_ctx); > mutex_lock(&acomp_ctx->mutex); > - obj = zpool_obj_read_begin(zpool, entry->handle, acomp_ctx->buffer); > + obj = zpool_obj_read_begin(zpool, entry->handle, acomp_ctx->buffers[0]); > > /* > * zpool_obj_read_begin() might return a kmap address of highmem when > - * acomp_ctx->buffer is not used. However, sg_init_one() does not > - * handle highmem addresses, so copy the object to acomp_ctx->buffer. > + * acomp_ctx->buffers[0] is not used. However, sg_init_one() does not > + * handle highmem addresses, so copy the object to acomp_ctx->buffers[0]. > */ > if (virt_addr_valid(obj)) { > src = obj; > } else { > - WARN_ON_ONCE(obj == acomp_ctx->buffer); > - memcpy(acomp_ctx->buffer, obj, entry->length); > - src = acomp_ctx->buffer; > + WARN_ON_ONCE(obj == acomp_ctx->buffers[0]); > + memcpy(acomp_ctx->buffers[0], obj, entry->length); > + src = acomp_ctx->buffers[0]; > } > > sg_init_one(&input, src, entry->length); > -- > 2.27.0 >
