On Tue, 1 Sep 2026 14:04:22 -0400 Nhat Pham <[email protected]> wrote:
> On Tue, Sep 1, 2026 at 12:13 PM Joshua Hahn <[email protected]> wrote: > > > > The test_no_invasive_cgroup_shrink selftest checks that when a cgroup > > has zswapped out more pages than memory.zswap.max, that it does not > > trigger writeback for other cgroups. To do this, it compares the > > writeback count in a control cgroup and makes sure that it is 0, > > and compares it to the writeback count in a aggressor cgroup who > > does expect to see writeback. > > > > When the zswap shrinker is enabled however, there is an additional path > > to zswap writeback, which can happen independently of reaching the > > memory.zswap.max limit. > > > > The writeback counter cannot distinguish between invasive noisy-neighbor > > driven writeback and the zswap shrinker work, so the test becomes > > invalid. Hi Nhat! Thanks for the quick review on this. > I think writeback in the control group (zw_group) happens right during > the first round of memory allocation, but there shouldn't be any on > the second round (as the second round involves writing to wb_group > only). So if we read zswap writeback counter of that cgroup (zw_group) > right after that first allocation round, and make sure delta = 0 after > the second round, then that should work for both shrinker_enabled = Y > v.s N. That is very smart and much better than just skipping the test, I'll take your approach. I've sent a v2 in [1]. Have a great day Nhat! Thank you again! Joshua [1] https://lore.kernel.org/all/[email protected]/
