On Fri, May 08, 2020 at 07:48:01AM +0800, Huang, Ying wrote: >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 Where's that happening, or is the comment out of date?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. > Yep, NP. For the code itself, do you have some comment? >I remember that Matthew thought that the swap code should work >reasonably even for garbage PTE. > >Best Regards, >Huang, Ying > >>>Best Regards, >>>Huang, Ying -- Wei Yang Help you, Help me
