Wei Yang <richard.weiyang@xxxxxxxxx> writes: > On Wed, May 06, 2020 at 04:22:54PM +0800, Huang, Ying wrote: >>Wei Yang <richard.weiyang@xxxxxxxxx> writes: >> >>> On Fri, May 01, 2020 at 03:48:53PM -0700, Andrew Morton wrote: >>>>On Fri, 1 May 2020 01:52:59 +0000 Wei Yang <richard.weiyang@xxxxxxxxx> wrote: >>>> >>>>> When the condition is true, there are two possibilities: >>>> >>>>I'm struggling with this one. >>>> >>>>> 1. count == SWAP_MAP_BAD >>>>> 2. count == (SWAP_MAP_MAX & COUNT_CONTINUED) == SWAP_MAP_SHMEM >>>> >>>>I'm not sure what 2. is trying to say. For a start, (SWAP_MAP_MAX & >>>>COUNT_CONTINUED) is zero. I guess it meant "|"? >>> >>> Oops, you are right. It should be (SWAP_MAP_MAX | COUNT_CONTINUED). >>> >>> Sorry for the confusion. >>> >>>> >>>>Also, the return value documentation says we return EINVAL for migration >>>>entries. Where's that happening, or is the comment out of date? >>>> >>> >>> Not paid attention to this. >>> >>> Take look into the code, I don't find a relationship between the swap count >>> and migration. Seems we just make a migration entry but not duplicate it. >>> If my understanding is correct. >> >>Per my understanding, one functionality of the error path is to catch >>the behavior that shouldn't happen at all. For example, if >>__swap_duplicate() is called for the migration entry because of some >>race condition. >> > > If __swap_duplicate() run for a migration entry, it returns since > get_swap_entry() couldn't find a swap_info_struct. So the return value is > -EINVAL. > > While when this situation would happen? And the race condition you mean is? Sorry for confusing. I don't mean there are some known race conditions in current kernel that will trigger the error code path. I mean we may use the error path to identify some race conditions in the future. I remember that Matthew thought that the swap code should work reasonably even for garbage PTE. Best Regards, Huang, Ying >>Best Regards, >>Huang, Ying
