Messages in this thread |  | | Date | Wed, 2 Jan 2013 16:09:04 -0800 | Subject | Re: mmap() scalability in the presence of the MAP_POPULATE flag | From | Michel Lespinasse <> |
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On Wed, Jan 2, 2013 at 8:50 AM, Roman Dubtsov <dubtsov@gmail.com> wrote: > Concurrent mmap() calls from the same process are serialized via downing > mm->mmap_sem for write. This means that operations like populating the > pages which do not alter vmas are also performed serially. Anecdotal > data from two machines I have access to is that populating pages by > touching them in a loop outside of mmap() improves performance of the > synthetic micro-benchmark by ~40% in the worst case. A crude patch that > modifies vm_mmap_pgoff() to call make_pages_present() outside of > do_mmap_pgoff() after upping the semaphore when MAP_POPULATE is present > brings identical performance improvement. > > Is there an interest in fixing this or concurrent mmaps() from the same > process are too much of a corner case to worry about it?
Funny this comes up again. I actually have a patch series that is supposed to do that: [PATCH 0/9] Avoid populating unbounded num of ptes with mmap_sem held
However, the patches are still pending, didn't get much review (probably not enough for Andrew to take them at this point), and I think everyone forgot about them during the winter break.
Care to have a look at that thread and see if it works for you ?
(caveat: you will possibly also need "[PATCH 10/9] mm: make do_mmap_pgoff return populate as a size in bytes, not as a bool" to make the series actually work for you)
-- Michel "Walken" Lespinasse A program is never fully debugged until the last user dies.
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