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SubjectRe: [RFC v2 29/34] mm: slub: Move flush_cpu_slab() invocations __free_slab() invocations out of IRQ context
On Thu, Jun 10, 2021 at 10:32:14AM +0200, Vlastimil Babka wrote:
> >> static void flush_all(struct kmem_cache *s)
> >> {
> >> - on_each_cpu_cond(has_cpu_slab, flush_cpu_slab, s, 1);
> >> + struct slub_flush_work *sfw;
> >> + unsigned int cpu;
> >> +
> >> + cpus_read_lock();
> >> + mutex_lock(&flush_lock);
> >> +
> >
> > Hi, Vlastimil! Could you please point why do you lock cpus first and
> > mutex only after? Why not mutex_lock + cpus_read_lock instead?
>
> Good question! I must admit I didn't think about it much and just followed the
> order that was in the original Sebastian's patch [1]
> But there was a good reason for this order as some paths via
> __kmem_cache_shutdown() and __kmem_cache_shrink() were alreadu called under
> cpus_read_lock. Meanwhile mainline (me, actually) removed those, so now it
> doesn't seem to be a need to keep this order anymore and we could switch it.

I bet we should switch :) But we can do that on top later, once series is
settled down and merged.

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