On Tue, Dec 04, 2012 at 06:37:41AM -0800, Michel Lespinasse wrote:

On Mon, Dec 3, 2012 at 6:17 AM, Mel Gorman [off-list ref] wrote:

quoted

On Sat, Dec 01, 2012 at 09:15:38PM +0100, Ingo Molnar wrote:

quoted

@@ -732,7 +732,7 @@ static int page_referenced_anon(struct p
      struct anon_vma_chain *avc;
      int referenced = 0;

-     anon_vma = page_lock_anon_vma(page);
+     anon_vma = page_lock_anon_vma_read(page);
      if (!anon_vma)
              return referenced;

This is a slightly trickier one as this path is called from reclaim. It does
open the possibility that reclaim can stall something like a parallel fork
or anything that requires the anon_vma rwsem for a period of time. I very
severely doubt it'll really be a problem but keep an eye out for bug reports
related to delayed mmap/fork/anything_needing_write_lock during page reclaim.

I don't see why this would be a problem - rwsem does implement
reader/writer fairness, so having some sites do a read lock instead of
a write lock shouldn't cause the write lock sites to starve. Is this
what you were worried about ?

Yes. I did not expect they would be starved forever, just delayed longer
than they might have been before. I would be very surprised if there is
anything other than a synthetic case that will really care but I've been
"very surprised" before :)

-- 
Mel Gorman
SUSE Labs

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