Hi Michel, > Hello, > > > I would like to resurect this, as I am seeing problems during a large > > mlock (many GB). The mlock takes a long time to complete > > (__mlock_vma_pages_range() is loading pages from disk), there is > > memory pressure as some pages have to be evicted to make room for the > > large mlock, and the LRU algorithm performs badly with the high amount > > of pages still on LRU list - PageMlocked has not been set yet - while > > their VMA is already VM_LOCKED. > > > > One approach I am considering would be to modify > > __mlock_vma_pages_range() and it call sites so the mmap sem is only > > read-owned while __mlock_vma_pages_range() runs. The mlock handling > > code in try_to_unmap_one() would then be able to acquire the > > mmap_sem() and help, as it is designed to do. > > I would like to talk historical story a bit. Originally, Lee designed it as you proposed. > but Linus refused it. He thought ro-rwsem is bandaid fix. That is one of reason that > some developers seeks proper mmap_sem dividing way. While in airplane to come back from KS and LPC, I was thinking this issue. now I think we can solve this issue. can you please hear my idea? Now, mlock has following call flow sys_mlock down_write(mmap_sem) do_mlock() for-each-vma mlock_fixup() __mlock_vma_pages_range() __get_user_pages() up_write(mmap_sem) And, someone tried following change and Linus refuse it because releasing mmap_sem while mlock() syscall can makes nasty race issue. He storongly requested we don't release mmap_sem while processing mlock(). sys_mlock down_write(mmap_sem) do_mlock() for-each-vma downgrade_write(mmap_sem) mlock_fixup() __mlock_vma_pages_range() __get_user_pages() up_read(mmap_sem) // race here down_write(mmap_sem) up_write(mmap_sem) Then, I'd propose two phase mlock. that said, sys_mlock down_write(mmap_sem) do_mlock() for-each-vma turn on VM_LOCKED and merge/split vma downgrade_write(mmap_sem) for-each-vma mlock_fixup() __mlock_vma_pages_range() up_read(mmap_sem) Usually, kernel developers strongly dislike two phase thing beucase it's slow. but at least _I_ think it's ok in this case. because mlock is really really slow syscall, it often take a few *miniture*. then, A few microsecond slower is not big matter. What do you think? -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom policy in Canada: sign http://dissolvethecrtc.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>