On Mon, 9 Jun 2025 10:56:46 +0200 Vlastimil Babka <vbabka@xxxxxxx> wrote: > On 6/9/25 10:52 AM, Vlastimil Babka wrote: > > On 6/9/25 10:31 AM, Ritesh Harjani (IBM) wrote: > >> Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx> writes: > >> > >>> On 2025/6/9 15:35, Michal Hocko wrote: > >>>> On Mon 09-06-25 10:57:41, Ritesh Harjani wrote: > >>>>> > >>>>> Any reason why we dropped the Fixes tag? I see there were a series of > >>>>> discussion on v1 and it got concluded that the fix was correct, then why > >>>>> drop the fixes tag? > >>>> > >>>> This seems more like an improvement than a bug fix. > >>> > >>> Yes. I don't have a strong opinion on this, but we (Alibaba) will > >>> backport it manually, > >>> > >>> because some of user-space monitoring tools depend > >>> on these statistics. > >> > >> That sounds like a regression then, isn't it? > > > > Hm if counters were accurate before f1a7941243c1 and not afterwards, and > > this is making them accurate again, and some userspace depends on it, > > then Fixes: and stable is probably warranted then. If this was just a > > perf improvement, then not. But AFAIU f1a7941243c1 was the perf > > improvement... > > Dang, should have re-read the commit log of f1a7941243c1 first. It seems > like the error margin due to batching existed also before f1a7941243c1. > > " This patch converts the rss_stats into percpu_counter to convert the > error margin from (nr_threads * 64) to approximately (nr_cpus ^ 2)." > > so if on some systems this means worse margin than before, the above > "if" chain of thought might still hold. f1a7941243c1 seems like a good enough place to tell -stable maintainers where to insert the patch (why does this sound rude). The patch is simple enough. I'll add fixes:f1a7941243c1 and cc:stable and, as the problem has been there for years, I'll leave the patch in mm-unstable so it will eventually get into LTS, in a well tested state.
