Hello.
On Thu, Mar 30, 2023 at 07:17:57PM +0000, Yosry Ahmed <yosryahmed@xxxxxxxxxx> wrote:
> static void __mem_cgroup_flush_stats(void)
> {
> - unsigned long flag;
> -
> - if (!spin_trylock_irqsave(&stats_flush_lock, flag))
> + /*
> + * We always flush the entire tree, so concurrent flushers can just
> + * skip. This avoids a thundering herd problem on the rstat global lock
> + * from memcg flushers (e.g. reclaim, refault, etc).
> + */
> + if (atomic_read(&stats_flush_ongoing) ||
> + atomic_xchg(&stats_flush_ongoing, 1))
> return;
I'm curious about why this instead of
if (atomic_xchg(&stats_flush_ongoing, 1))
return;
Is that some microarchitectural cleverness?
Thanks,
Michal
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