We have a threaded page fault scaling test that is performing very poorly due to the use of the page_table_lock in the THP fault code path. By replacing the page_table_lock with the ptl on the pud_page (need CONFIG_SPLIT_PTLOCKS for this to work), we're able to increase the granularity of the locking here by a factor of 512, i.e. instead of locking all 256TB of addressable memory, we only lock the 512GB that is handled by a single pud_page. The test I'm running creates 512 threads, pins each thread to a cpu, has the threads allocate 512mb of memory each and then touch the first byte of each 4k chunk of the allocated memory. Here are the timings from this test on 3.11-rc7, clean, THP on: real 22m50.904s user 15m26.072s sys 11430m19.120s And here are the timings with my modified kernel, THP on: real 0m37.018s user 21m39.164s sys 155m9.132s As you can see, we get a huge performance boost by locking a more targeted chunk of memory instead of locking the whole page table. At this point, I'm comfortable saying that there are obvious benefits to increasing the granularity of the locking, but I'm not sure that I've done this in the best way possible. Mainly, I'm not positive that using the pud_page lock actually protects everything that we're concerned about locking here. I'm hoping that everyone can provide some input on whether or not this seems like a reasonable move to make and, if so, confirm that I've locked things appropriately. As a side note, we still have some pretty significant scaling issues with this test, both with THP on, and off. I'm cleaning up the locking here first as this is causing the biggest performance hit. Alex Thorlton (1): Change THP code to use pud_page(pud)->ptl lock instead of page_table_lock mm/huge_memory.c | 4 ++-- mm/memory.c | 6 +++--- 2 files changed, 5 insertions(+), 5 deletions(-) -- 1.7.12.4 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx"> email@xxxxxxxxx </a>