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From: Yosry Ahmed To: Kanchana P Sridhar Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, hannes@cmpxchg.org, nphamcs@gmail.com, chengming.zhou@linux.dev, usamaarif642@gmail.com, ryan.roberts@arm.com, 21cnbao@gmail.com, ying.huang@linux.alibaba.com, akpm@linux-foundation.org, linux-crypto@vger.kernel.org, herbert@gondor.apana.org.au, davem@davemloft.net, clabbe@baylibre.com, ardb@kernel.org, ebiggers@google.com, surenb@google.com, kristen.c.accardi@intel.com, wajdi.k.feghali@intel.com, vinodh.gopal@intel.com Subject: Re: [PATCH v8 13/14] mm: zswap: Allocate pool batching resources if the compressor supports batching. Message-ID: References: <20250303084724.6490-1-kanchana.p.sridhar@intel.com> <20250303084724.6490-14-kanchana.p.sridhar@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250303084724.6490-14-kanchana.p.sridhar@intel.com> X-Migadu-Flow: FLOW_OUT X-Rspam-User: X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 112D420023 X-Stat-Signature: cj1y6run8yyht5ujty5ajubsbqhqep4s X-HE-Tag: 1741291272-944394 X-HE-Meta: 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 4/gQWv2P Ru2mPDuTNmBybr4M4V2j3RsHbBxStsJT8/ykOh/blqFKxDAgv2TMoNYIiR7T27LgsUcW2L/xmYTsEmD4qJ/dzbo0y5RTu6BKoTHXaQOkOgoXIr/fgDZ2sKdHwnJBMBfKdq9juP54eDniWjbkgARLaUEz8Wx20uljYozstqOo0qV0A4+otXm5luGfxzZvMoTVaAY3hEJbNsJ1IsuFmtWAiewYfEfppxaJBfX6Qnd3YMIcY10yBWeayhdjzi9PiyYPWACbtabLtkmcIwKn7L+MRSKy4Lw== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Mar 03, 2025 at 12:47:23AM -0800, Kanchana P Sridhar wrote: > 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. That's two pointers per-CPU (i.e. 16 bytes on x86_64), right? Please call that out in the commit log. > > Signed-off-by: Kanchana P Sridhar > --- > 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. > + */ That's too verbose. Let's do something like: /* Limit the batch size to limit per-CPU memory usage for reqs and buffers */ #define ZSWAP_MAX_BATCH_SIZE 8U > +#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])) Hmm I just realized we check IS_ERR_OR_NULL() here for the requests, but only a NULL check in zswap_cpu_comp_prepare(). We also check IS_ERR_OR_NULL here for acomp, but only IS_ERR() in zswap_cpu_comp_prepare(). This doesn't make sense. Would you be able to include a patch before this one to make these consistent? I can also send a follow up patch. > + acomp_request_free(acomp_ctx->reqs[i]); Please add braces for the for loop here for readability, since the body has more than one line, even if it's technically not required. > + 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. > + */ I am not sure I understand. Does this say that we assume that scomp or non-poll acomp will never use batching so having a single "wait" is fine? If so, this needs to be enforced at runtime or at least have a warning, and not just mentioned in a comment, in case batching support is ever added for these. Please clarify. We should also probably merge the comments above crypto_init_wait() and acomp_request_set_callback() now. > crypto_init_wait(&acomp_ctx->wait); > > /*