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SubjectRe: [PATCH v8 03/17] mm: Assign id to every memcg-aware shrinker
On Tue, Jul 03, 2018 at 10:47:44AM -0700, Matthew Wilcox wrote:
> On Tue, Jul 03, 2018 at 08:46:28AM -0700, Shakeel Butt wrote:
> > On Tue, Jul 3, 2018 at 8:27 AM Matthew Wilcox <willy@infradead.org> wrote:
> > > This will actually reduce the size of each shrinker and be more
> > > cache-efficient when calling the shrinkers. I think we can also get
> > > rid of the shrinker_rwsem eventually, but let's leave it for now.
> >
> > Can you explain how you envision shrinker_rwsem can be removed? I am
> > very much interested in doing that.
>
> Sure. Right now we have 3 uses of shrinker_rwsem -- two for adding and
> removing shrinkers to the list and one for walking the list. If we switch
> to an IDR then we can use a spinlock for adding/removing shrinkers and
> the RCU read lock for looking up an entry in the IDR each iteration of
> the loop.
>
> We'd need to stop the shrinker from disappearing underneath us while we
> drop the RCU lock, so we'd need a refcount in the shrinker, and to free
> the shrinkers using RCU. We do similar things for other data structures,
> so this is all pretty well understood.

<censored>
struct super_block {
...
struct shrinker s_shrink; /* per-sb shrinker handle */
...
}
<censored>

What was that about refcount in the shrinker and taking over the lifetime
rules of the objects it might be embedded into, again?

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