Re: [PATCH v2] vmscan: limit concurrent reclaimers in shrink_zone

[Rik van Riel]

On 12/18/2009 05:27 AM, KOSAKI Motohiro wrote:
> > KOSAKI Motohiro wrote:

> > Finally, having said all that, the system still struggles reclaiming
> > memory with
> > ~10000 processes trying at the same time, you fix one bottleneck and it
> > moves
> > somewhere else.  The latest run showed all but one running process
> > spinning in
> > page_lock_anon_vma() trying for the anon_vma_lock.  I noticed that there
> > are
> > ~5000 vma's linked to one anon_vma, this seems excessive!!!
> >
> > I changed the anon_vma->lock to a rwlock_t and page_lock_anon_vma() to use
> > read_lock() so multiple callers could execute the page_reference_anon code.
> > This seems to help quite a bit.
>
> Ug. no. rw-spinlock is evil. please don't use it. rw-spinlock has bad
> performance characteristics, plenty read_lock block write_lock for very
> long time.
>
> and I would like to confirm one thing. anon_vma design didn't change
> for long year. Is this really performance regression? Do we strike
> right regression point?

In 2.6.9 and 2.6.18 the system would hit different contention
points before getting to the anon_vma lock.  Now that we've
gotten the other contention points out of the way, this one
has finally been exposed.

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