On Wed, Mar 11, 2026 at 9:07 PM Li Wang <[email protected]> wrote: > > In attempt_writeback(), a memsize of 4M only covers 64 pages on 64K > page size systems. When memory.reclaim is called, the kernel prefers > reclaiming clean file pages (binary, libc, linker, etc.) over swapping > anonymous pages. With only 64 pages of anonymous memory, the reclaim > target can be largely or entirely satisfied by dropping file pages, > resulting in very few or zero anonymous pages being pushed into zswap. > > This causes zswap_usage to be extremely small or zero, making > zswap_usage/2 insufficient to create meaningful writeback pressure. > The test then fails because no writeback is triggered. > > On 4K page size systems this is not an issue because 4M covers 1024 > pages, and file pages are a small fraction of the reclaim target. > > Fix this by always allocating 1024 pages regardless of page size. > This ensures enough anonymous pages to reliably populate zswap and > trigger writeback, while keeping the original 4M allocation on 4K > page size systems. > > === Error Log === > # uname -rm > 6.12.0-211.el10.ppc64le ppc64le > > # getconf PAGESIZE > 65536 > > # ./test_zswap > TAP version 13 > 1..7 > ok 1 test_zswap_usage > ok 2 test_swapin_nozswap > ok 3 test_zswapin > not ok 4 test_zswap_writeback_enabled > ... > > Signed-off-by: Li Wang <[email protected]> > Cc: Johannes Weiner <[email protected]> > Cc: Michal Hocko <[email protected]> > Cc: Michal Koutný <[email protected]> > Cc: Muchun Song <[email protected]> > Cc: Nhat Pham <[email protected]> > Cc: Tejun Heo <[email protected]> > Cc: Roman Gushchin <[email protected]> > Cc: Shakeel Butt <[email protected]> > Cc: Yosry Ahmed <[email protected]>
Acked-by: Yosry Ahmed <[email protected]>
