On Mon, Aug 24, 2015 at 4:30 PM, Vlastimil Babka <vbabka@xxxxxxx> wrote: > On 08/24/2015 12:17 PM, Konstantin Khlebnikov wrote: >>> >>> >>> I am in the middle of implementing lock on fault this way, but I cannot >>> see how we will hanlde mremap of a lock on fault region. Say we have >>> the following: >>> >>> addr = mmap(len, MAP_ANONYMOUS, ...); >>> mlock(addr, len, MLOCK_ONFAULT); >>> ... >>> mremap(addr, len, 2 * len, ...) >>> >>> There is no way for mremap to know that the area being remapped was lock >>> on fault so it will be locked and prefaulted by remap. How can we avoid >>> this without tracking per vma if it was locked with lock or lock on >>> fault? >> >> >> remap can count filled ptes and prefault only completely populated areas. > > > Does (and should) mremap really prefault non-present pages? Shouldn't it > just prepare the page tables and that's it? As I see mremap prefaults pages when it extends mlocked area. Also quote from manpage : If the memory segment specified by old_address and old_size is locked : (using mlock(2) or similar), then this lock is maintained when the segment is : resized and/or relocated. As a consequence, the amount of memory locked : by the process may change. > >> There might be a problem after failed populate: remap will handle them >> as lock on fault. In this case we can fill ptes with swap-like non-present >> entries to remember that fact and count them as should-be-locked pages. > > > I don't think we should strive to have mremap try to fix the inherent > unreliability of mmap (MAP_POPULATE)? I don't think so. MAP_POPULATE works only when mmap happens. Flag MREMAP_POPULATE might be a good idea. Just for symmetry. -- 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>