Messages in this thread | | | Date | Tue, 3 Oct 2023 09:13:09 -0400 | From | Johannes Weiner <> | Subject | Re: [PATCH v2 2/2] mm: memcg: normalize the value passed into memcg_rstat_updated() |
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On Fri, Sep 22, 2023 at 05:57:40PM +0000, Yosry Ahmed wrote: > memcg_rstat_updated() uses the value of the state update to keep track > of the magnitude of pending updates, so that we only do a stats flush > when it's worth the work. Most values passed into memcg_rstat_updated() > are in pages, however, a few of them are actually in bytes or KBs. > > To put this into perspective, a 512 byte slab allocation today would > look the same as allocating 512 pages. This may result in premature > flushes, which means unnecessary work and latency.
Yikes.
I'm somewhat less concerned about the performance as I am about the variance in flushing cost that could be quite difficult to pinpoint. IMO this is a correctness fix and a code cleanup, not a performance thing.
> Normalize all the state values passed into memcg_rstat_updated() to > pages. Round up non-zero sub-page to 1 page, because > memcg_rstat_updated() ignores 0 page updates. > > Fixes: 5b3be698a872 ("memcg: better bounds on the memcg stats updates") > Signed-off-by: Yosry Ahmed <yosryahmed@google.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
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