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[34.125.181.99]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2a2f3c82a10sm30046535ad.26.2025.12.19.12.07.11 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 19 Dec 2025 12:07:12 -0800 (PST) Date: Fri, 19 Dec 2025 20:07:08 +0000 From: Sami Tolvanen To: Eric Biggers Cc: dm-devel@lists.linux.dev, Alasdair Kergon , Mike Snitzer , Mikulas Patocka , Benjamin Marzinski , Eran Messeri , linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 2/7] dm-verity: make dm_verity_fec_io::bufs variable-length Message-ID: <20251219200708.GA2662043@google.com> References: <20251219192909.385494-1-ebiggers@kernel.org> <20251219192909.385494-3-ebiggers@kernel.org> Precedence: bulk X-Mailing-List: dm-devel@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20251219192909.385494-3-ebiggers@kernel.org> On Fri, Dec 19, 2025 at 11:29:04AM -0800, Eric Biggers wrote: > When correcting a data block, the FEC code performs optimally when it > has enough buffers to hold all the needed RS blocks. That number of > buffers is '1 << (v->data_dev_block_bits - DM_VERITY_FEC_BUF_RS_BITS)'. > > However, since v->data_dev_block_bits isn't a compile-time constant, the > code actually used PAGE_SHIFT instead. > > With the traditional PAGE_SIZE == data_block_size == 4096, this was > fine. However, when PAGE_SIZE > data_block_size, this wastes space. > E.g., with data_block_size == 4096 && PAGE_SIZE == 16384, struct > dm_verity_fec_io is 9240 bytes, when in fact only 3096 bytes are needed. > > Fix this by making dm_verity_fec_io::bufs a variable-length array. > > This makes the macros DM_VERITY_FEC_BUF_MAX and > fec_for_each_extra_buffer() no longer apply, so remove them. For > consistency, and because DM_VERITY_FEC_BUF_PREALLOC is fixed at 1 and > was already assumed to be 1 (considering that mempool_alloc() shouldn't > be called in a loop), also remove the related macros > DM_VERITY_FEC_BUF_PREALLOC and fec_for_each_prealloc_buffer(). > > Signed-off-by: Eric Biggers Reviewed-by: Sami Tolvanen Sami