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Date:   Thu, 14 Jan 2021 09:04:26 +0000 (UTC)
From:   Christoph Lameter <>
To:     Jann Horn <>
cc:     Vlastimil Babka <>,
        Pekka Enberg <>,
        David Rientjes <>,
        Joonsoo Kim <>,
        Andrew Morton <>,
        Linux-MM <>,
        kernel list <>,
        Thomas Gleixner <>,
        Sebastian Andrzej Siewior <>,
        Roman Gushchin <>,
        Johannes Weiner <>,
        Shakeel Butt <>,
        Suren Baghdasaryan <>,
        Minchan Kim <>,
        Michal Hocko <>
Subject: Re: SLUB: percpu partial object count is highly inaccurate, causing
 some memory wastage and maybe also worse tail latencies?

On Wed, 13 Jan 2021, Jann Horn wrote:

> Some brainstorming:
> Maybe you could have an atomic counter in kmem_cache_cpu that tracks
> the number of empty frozen pages that are associated with a specific
> CPU? So the freeing slowpath would do its cmpxchg_double, and if the

The latencies of these functions are so low that any additional counter
will have significant performance impacts. An atomic counter would be waay
out there.

> You could additionally have a plain percpu counter, not tied to the

The performance critical counters are already all per cpu. I enhanced the
percpu subsystem specifically to support latency critical operations in
the fast path of the slab allocators.

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