Re: [PATCH v2 00/28] Eliminate Dying Memory Cgroup

[Harry Yoo]

On Wed, Dec 24, 2025 at 02:51:12PM +0000, Yosry Ahmed wrote:
> December 24, 2025 at 12:43 AM, "Harry Yoo" <harry.yoo@xxxxxxxxxx> wrote:
> 
> 
> > 
> > On Tue, Dec 23, 2025 at 08:04:50PM +0000, Yosry Ahmed wrote:
> > 
> > > 
> > > I think there might be a problem with non-hierarchical stats on cgroup
> > >  v1, I brought it up previously [*]. I am not sure if this was addressed
> > >  but I couldn't immediately find anything.
> > > 
> > Hi, Yosry. Thanks for bringing this up!
> > 
> > > 
> > > In short, if memory is charged to a dying cgroup at the time of
> > >  reparenting, when the memory gets uncharged the stats updates will occur
> > >  at the parent. This will update both hierarchical and non-hierarchical
> > >  stats of the parent, which would corrupt the parent's non-hierarchical
> > >  stats (because those counters were never incremented when the memory was
> > >  charged).
> > > 
> > Hmm, I wonder if this only applies to LRU pages.
> > 
> > In theory we should have this problem for NR_SLAB{UN,}RECLAIMABLE_B
> > because we already reparent objcgs, or am I missing something?
> 
> We do, but we don't expose these stats in cgroup v1, and we don't expose non-hierarchical stats in cgroup v2.

Oops, right.
I was missing that. Thanks!

-- 
Cheers,
Harry / Hyeonggon