Re: [PATCH 2/2] mm/migration: Make rmap_walk_anon() andtry_to_unmap_anon() more scalable

[Michel Lespinasse]

On Mon, Dec 3, 2012 at 6:17 AM, Mel Gorman <mgorman@xxxxxxx> wrote:
> On Sat, Dec 01, 2012 at 09:15:38PM +0100, Ingo Molnar wrote:
>> @@ -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 ?

-- 
Michel "Walken" Lespinasse
A program is never fully debugged until the last user dies.
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