On Tue, Apr 29, 2025 at 09:38:28AM +0800, Yu Kuai wrote: > Hi, > > 在 2025/04/29 2:07, Keith Busch 写道: >> On Mon, Apr 28, 2025 at 07:09:50AM -0700, Christoph Hellwig wrote: >>> A lot of complexity in brd stems from the fact that it tries to handle >>> I/O spanning two backing pages. Instead limit the size of a single >>> bvec iteration so that it never crosses a page boundary and remove all >>> the now unneeded code. >> >> Doesn't bio_for_each_segment() already limit bvecs on page boundaries? >> You'd need to use bio_for_each_bvec() to get multi-page bvecs. > > I think it only limit bvecs on page boundaries on the issue side, not > disk side. > > For example, if user issue an IO (2k + 4k), will bio_for_each_segment() > split this IO into (2k + 2k) and (4k + 2k), I do not test yet, but I > think the answer is no. Exactly. I got this wrong with zram, where it only triggers with larger than 4k page sizes, and I got this wrong here on my first attempt as well. Fortunately testing found it quickly. I thought the comment and commit message document the issue well enough, but I'm open to better wording.
