Messages in this thread | | | Subject | mmap() scalability in the presence of the MAP_POPULATE flag | From | Roman Dubtsov <> | Date | Wed, 02 Jan 2013 23:50:18 +0700 |
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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?
Regards, Roma
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