Messages in this thread | | | Subject | Re: mmap() scalability in the presence of the MAP_POPULATE flag | From | Roman Dubtsov <> | Date | Fri, 04 Jan 2013 00:09:37 +0700 |
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On Wed, 2013-01-02 at 16:09 -0800, Michel Lespinasse wrote: > > 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)
I applied the patches on top of 3.7.1. Here're the results for 4 threads concurrently mmap()-ing 10 64MB buffers in a loop without munmap()-s. The data is from a Nehalem i7-920 single-socket 4-core CPU. I've also added the older data I have for the 3.6.11 (patched and not) for reference.
3.6.11 vanilla, do not populate: 0.001 seconds 3.6.11 vanilla, populate via a loop: 0.216 seconds 3.6.11 vanilla, populate via MAP_POPULATE: 0.358 seconds
3.6.11 + crude patch, do not populate: 0.002 seconds 3.6.11 + crude patch, populate via loop: 0.215 seconds 3.6.11 + crude patch, populate via MAP_POPULATE: 0.217 seconds
3.7.1 vanilla, do not populate: 0.001 seconds 3.7.1 vanilla, populate via a loop: 0.216 seconds 3.7.1 vanilla, populate via MAP_POPULATE: 0.411 seconds
3.7.1 + patch series, do not populate: 0.001 seconds 3.7.1 + patch series, populate via loop: 0.216 seconds 3.7.1 + patch series, populate via MAP_POPULATE: 0.273 seconds
So, the patch series mentioned above do improve performance but as far as I can read the benchmarking data there's still some performance left on the table.
Regards, Roma
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