Messages in this thread | | | Date | Mon, 30 May 2022 20:29:30 +0200 | Subject | Re: [PATCH v4] mm: Avoid unnecessary page fault retires on shared memory types | From | Christian Borntraeger <> |
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Am 30.05.22 um 18:00 schrieb Peter Xu: > On Mon, May 30, 2022 at 11:52:54AM -0400, Peter Xu wrote: >> On Mon, May 30, 2022 at 11:35:10AM +0200, Christian Borntraeger wrote: >>> >>> >>> Am 29.05.22 um 22:33 schrieb Heiko Carstens: >>> [...] >>>> >>>> Guess the patch below on top of your patch is what we want. >>>> Just for clarification: if gmap is not NULL then the process is a kvm >>>> process. So, depending on the workload, this optimization makes sense. >>>> >>>> diff --git a/arch/s390/mm/fault.c b/arch/s390/mm/fault.c >>>> index 4608cc962ecf..e1d40ca341b7 100644 >>>> --- a/arch/s390/mm/fault.c >>>> +++ b/arch/s390/mm/fault.c >>>> @@ -436,12 +436,11 @@ static inline vm_fault_t do_exception(struct pt_regs *regs, int access) >>>> /* The fault is fully completed (including releasing mmap lock) */ >>>> if (fault & VM_FAULT_COMPLETED) { >>>> - /* >>>> - * Gmap will need the mmap lock again, so retake it. TODO: >>>> - * only conditionally take the lock when CONFIG_PGSTE set. >>>> - */ >>>> - mmap_read_lock(mm); >>>> - goto out_gmap; >>>> + if (gmap) { >>>> + mmap_read_lock(mm); >>>> + goto out_gmap; >>>> + } >>>> + goto out; > > Hmm, right after I replied I found "goto out" could be problematic, since > all s390 callers of do_exception() will assume it an error condition (side > note: "goto out_gmap" contains one step to clear "fault" to 0). I'll > replace this with "return 0" instead if it looks good to both of you. > > I'll wait for a confirmation before reposting. Thanks,
Yes, that sounds good and thank you for double checking.
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