On Fri, Apr 14, 2023 at 4:49 PM Suren Baghdasaryan <surenb@xxxxxxxxxx> wrote: > > On Fri, Apr 14, 2023 at 3:35 PM Peter Xu <peterx@xxxxxxxxxx> wrote: > > > > Hi, Suren, > > > > On Fri, Apr 14, 2023 at 03:14:23PM -0700, Suren Baghdasaryan wrote: > > > > It also already ignores invalid faults: > > > > > > > > if (ret & (VM_FAULT_ERROR | VM_FAULT_RETRY)) > > > > return; > > > > > > Can there be a case of (!VM_FAULT_ERROR && VM_FAULT_RETRY) - basically > > > we need to retry but no errors happened? If so then this condition > > > would double-count pagefaults in such cases. > > > > If ret==VM_FAULT_RETRY it should return here already, so I assume > > mm_account_fault() itself is fine regarding fault retries? > > > > Note that I think "ret & (VM_FAULT_ERROR | VM_FAULT_RETRY)" above means > > "either ERROR or RETRY we'll skip the accounting". > > > > IMHO we should have 3 cases here: > > > > - ERROR && !RETRY > > error triggered of any kind > > > > - RETRY && !ERROR > > we need to try one more time > > > > - !RETRY && !ERROR > > we finished the fault > > After looking some more into mm_account_fault(), I think it would be > fine to count the faults which produced errors. IIUC these counters > represent the total number of faults, not the number of valid and > successful faults. If so then I think simply using VM_FAULT_RETRY > should be ok without considering all possible combinations. WDYT? I posted v2 at https://lore.kernel.org/all/20230415000818.1955007-1-surenb@xxxxxxxxxx/ Hopefully it's closer to what we want it to be. > > > > > I don't think ERROR & RETRY can even be set at the same time so I assume > > there's no option 4) - a RETRY should imply no ERROR already, even though > > it's still incomplete so need another attempt. > > > > Thanks, > > > > -- > > Peter Xu > >
