https://vmlinuz.pl/en/tags/nvme/ Recent content in Nvme on vmlinuz Hugo en 2025-2026 vmlinuz.pl Tue, 23 Jun 2026 10:00:00 +0100 https://vmlinuz.pl/en/posts/iomap-memset-iops/ Tue, 23 Jun 2026 10:00:00 +0100 https://vmlinuz.pl/en/posts/iomap-memset-iops/ <p>Sometimes you do not need a new driver or a rewritten subsystem to speed up the kernel. Sometimes it is enough to move a couple of lines that were doing pointless work for years. That is exactly what Fengnan Chang from ByteDance did: he moved a <code>memset()</code> call in the iomap layer and squeezed out about 5% more IOPS on ext4 and XFS. The change lands in Linux 7.2.</p> <h2 id="what-iomap-is">What iomap Is</h2> <p>iomap is the kernel&rsquo;s shared I/O mapping layer. Filesystems like ext4, XFS and exFAT use it to translate a file offset into a concrete location on the block device. The heart of the layer is the <code>iomap_iter()</code> loop: for a given file range it asks the filesystem to fill in a <code>struct iomap</code> describing the next contiguous chunk, performs the I/O, then asks for the next chunk until the range is done.</p>