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Thu, 12 Nov 2026 08:21:32 -0800 (PST) Date: Thu, 12 Nov 2026 11:21:31 -0500 From: Johannes Weiner To: Usama Arif Cc: Herbert Xu , davem@davemloft.net, terrelln@fb.com, dsterba@suse.com, yosry@kernel.org, nphamcs@gmail.com, chengming.zhou@linux.dev, Andrew Morton , linux-crypto@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, riel@surriel.com, shakeel.butt@linux.dev, kernel-team@meta.com Subject: Re: [PATCH 1/2] crypto: zstd - use vmalloc() for stream workspaces Message-ID: References: <20261111153532.1036709-1-usama.arif@linux.dev> <20261111153532.1036709-2-usama.arif@linux.dev> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261111153532.1036709-2-usama.arif@linux.dev> X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 514E3A000C X-Spam-Status: No, score=-10.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS autolearn=ham autolearn_force=no version=4.0.1 X-Stat-Signature: z4tceb1cfwjaccu4fmcf97k5mnxhe763 X-HE-Tag: 1794500495-284861 X-HE-Meta: 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 lB56w9xs NB+939YXH+vDH2Pa8CfwY06PVrONHjmjfBTpN8gRSae3H1QjIN70ryni2q5IxBPKqillt1aQtSOFJckWs1S0Yima8DfkRyiRtisPry+WHuQz2L75dMwrCdxjTyTevGmLni2FfyNTsdriU18PqzuOkTYf9lGABtyy8tRvNVPx/BS3IP9o6mivtfG1R7TAuFcxkMl44xHlyoyokGeCdN2wq4XuYQIAlELb5d63d8gu+8pR4Yz9SnWVe7wdRzHQSjzi6LAExVUQYN0xEggzUUG55k+QuJgnFZ/owo+z28LUDNpzGvmj0DkKiwieIht7HsRHw28M+nodaCM67nfEXWVv+NGektMApPGr7LSKRaPIOIYxV8t0lB0XBfkBeBDGRn3SURUhMRuQ7FcVNGOOPYPeMxxwKx0ob5qrdIw949ff1Ogb1zvU= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On Wed, Nov 11, 2026 at 07:07:39AM -0800, Usama Arif wrote: > The zstd acomp streams retain their workspaces after the last transform > has been freed. The first is allocated during transform initialization; > additional per-CPU streams are allocated on demand. They are released > when the algorithm is unregistered. > > In a 4 KiB-page x86-64 build, each stream requests 1,566,281 bytes. > If kvmalloc() succeeds via kmalloc(), it occupies an order-9 block > (2 MiB). vmalloc() needs 383 backing pages (1,532 KiB), 516 KiB fewer > per stream. Across 384 populated streams, that is 193.5 MiB less > workspace backing if all would have used kmalloc(). There is no such > gain when kvmalloc() already falls back to vmalloc(). > > Use vmalloc() and vfree() directly to avoid the high-order allocation. > This uses vmalloc address space, page tables and bookkeeping; the > figures above compare workspace backing only. > > Signed-off-by: Usama Arif Nice catch. Given the lifetime of these streams, there really isn't enough turnover to justify the kmalloc optimization to begin with. Reviewed-by: Johannes Weiner