On Sat 12-08-17 00:46:18, Tetsuo Handa wrote: > Michal Hocko wrote: > > On Fri 11-08-17 16:54:36, Tetsuo Handa wrote: > > > Michal Hocko wrote: > > > > On Fri 11-08-17 11:28:52, Tetsuo Handa wrote: > > > > > Will you explain the mechanism why random values are written instead of zeros > > > > > so that this patch can actually fix the race problem? > > > > > > > > I am not sure what you mean here. Were you able to see a write with an > > > > unexpected content? > > > > > > Yes. See http://lkml.kernel.org/r/201708072228.FAJ09347.tOOVOFFQJSHMFL@xxxxxxxxxxxxxxxxxxx . > > > > Ahh, I've missed that random part of your output. That is really strange > > because AFAICS the oom reaper shouldn't really interact here. We are > > only unmapping anonymous memory and even if a refault slips through we > > should always get zeros. > > > > Your test case doesn't mmap MAP_PRIVATE of a file so we shouldn't even > > get any uninitialized data from a file by missing CoWed content. The > > only possible explanations would be that a page fault returned a > > non-zero data which would be a bug on its own or that a file write > > extend the file without actually writing to it which smells like a fs > > bug to me. > > As I wrote at http://lkml.kernel.org/r/201708112053.FIG52141.tHJSOQFLOFMFOV@xxxxxxxxxxxxxxxxxxx , > I don't think it is a fs bug. Were you able to reproduce with other filesystems? I wonder what is different in my testing because I cannot reproduce this at all. Well, I had to reduce the number of competing writer threads to 128 because I quickly hit the trashing behavior with more of them (and 4 CPUs). I will try on a larger machine. -- Michal Hocko SUSE Labs -- 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>
