On 2023/12/14 08:18, Nhat Pham wrote: > On Wed, Dec 13, 2023 at 3:34 PM Yosry Ahmed <yosryahmed@xxxxxxxxxx> wrote: >> >> On Tue, Dec 12, 2023 at 8:18 PM Chengming Zhou >> <zhouchengming@xxxxxxxxxxxxx> wrote: >>> >>> Change the dstmem size from 2 * PAGE_SIZE to only one page since >>> we only need at most one page when compress, and the "dlen" is also >>> PAGE_SIZE in acomp_request_set_params(). If the output size > PAGE_SIZE >>> we don't wanna store the output in zswap anyway. >>> >>> So change it to one page, and delete the stale comment. >> >> I couldn't find the history of why we needed 2 * PAGE_SIZE, it would >> be nice if someone has the context, perhaps one of the maintainers. > > It'd be very nice indeed. > >> >> One potential reason is that we used to store a zswap header >> containing the swap entry in the compressed page for writeback >> purposes, but we don't do that anymore. Maybe we wanted to be able to >> handle the case where an incompressible page would exceed PAGE_SIZE >> because of that? > > It could be hmm. I didn't study the old zswap architecture too much, > but it has been 2 * PAGE_SIZE since the time zswap was first merged > last I checked. > I'm not 100% comfortable ACK-ing the undoing of something that looks > so intentional, but FTR, AFAICT, this looks correct to me. Right, there is no any history about the reason why we needed 2 pages. But obviously only one page is needed from the current code and no any problem found in the kernel build stress testing. Thanks!
