On Wed, Mar 20, 2024 at 06:55:05PM +0800, Pavel Tikhomirov wrote: > > > On 20/03/2024 18:28, Michal Hocko wrote: > > On Wed 20-03-24 18:03:30, Pavel Tikhomirov wrote: > > > In memory_max_write() we first set memcg->memory.max and only then > > > try to enforce it in loop. What if while we are in loop someone else > > > have changed memcg->memory.max but we are still trying to enforce > > > the old value? I believe this can lead to nasty consequence like getting > > > an oom on perfectly fine cgroup within it's limits or excess reclaim. > > > > I would argue that uncoordinated hard limit configuration can cause > > problems on their own. > > Sorry, didn't know that. > > > Beside how is this any different from changing > > the high limit while we are inside the reclaim loop? > > I believe reclaim loop rereads limits on each iteration, e.g. in > reclaim_high(), so it should always be enforcing the right limit. > > > > > > We also have exactly the same thing in memory_high_write(). > > > > > > So let's stop enforcing old limits if we already have a new ones. > > > > I do see any reasons why this would be harmful I just do not see why > > this is a real thing or why the new behavior is any better for racing > > updaters as those are not deterministic anyway. If you have any actual > > usecase then more details would really help to justify this change. > > > > The existing behavior makes some sense as it enforces the given limit > > deterministically. > > I don't have any actual problem, usecase or reproduce at hand, I only see a > potential problem: If the problem is only potential and also not very severe (it's not a crash or memory corruption or something like this), I'd say let's keep things as they are. Thanks!
