On Fri, Jan 03, 2025 at 02:12:36PM -0800, Bart Van Assche wrote: > On 1/2/25 6:01 PM, Ming Lei wrote: > > But why does DMA segment size have to be >= PAGE_SIZE(4KB, 64KB)? > > From the description of patch 5/8 of my patch series: "If the segment > size is smaller than the page size there may be multiple segments per > bvec even if a bvec only contains a single page." The current block > layer implementation is based on the assumption that a single page > fits in a single DMA segment. Please take a look at patch 5/8 of my > patch series. OK, I guess you agree it is one block layer constraint now, which need to be relaxed for both big logical block size and >4k PAGE_SIZE. Yes, your patch 5/8 is still needed. > > > From the link, you have storage controllers with DMA segment size which > > is less than 4K, which may never get supported by linux kernel. > > As mentioned in the cover letter of that patch series, I came up with > that patch series to support a DMA controller with max_segment_size of > 4 KiB on a system with a PAGE_SIZE of 16 KiB. Probably the conception of subpage need to avoid, because PAGE_SIZE is config option, and not see strong reason to couple with fixed & readable hardware properties with configurable kernel page size. Thanks, Ming
