Hi, David, On Tue, Jun 30, 2020 at 02:05:24PM -0700, David Rientjes wrote: > On Tue, 30 Jun 2020, Peter Xu wrote: > > > @@ -4408,6 +4440,34 @@ vm_fault_t handle_mm_fault(struct vm_area_struct *vma, unsigned long address, > > mem_cgroup_oom_synchronize(false); > > } > > > > + if (ret & (VM_FAULT_RETRY | VM_FAULT_ERROR)) > > + return ret; > > + > > + /* > > + * Do accounting in the common code, to avoid unnecessary > > + * architecture differences or duplicated code. > > + * > > + * We arbitrarily make the rules be: > > + * > > + * - Unsuccessful faults do not count (e.g. when the address wasn't > > + * valid). That includes arch_vma_access_permitted() failing above. > > + * > > + * So this is expressly not a "this many hardware page faults" > > + * counter. Use the hw profiling for that. > > + * > > + * - Incomplete faults do not count (e.g. RETRY). They will only > > + * count once completed. > > + * > > + * - The fault counts as a "major" fault when the final successful > > + * fault is VM_FAULT_MAJOR, or if it was a retry (which implies that > > + * we couldn't handle it immediately previously). > > + * > > + * - If the fault is done for GUP, regs will be NULL and no accounting > > + * will be done. > > + */ > > + mm_account_fault(regs, address, (ret & VM_FAULT_MAJOR) || > > + (flags & FAULT_FLAG_TRIED)); > > + > > return ret; > > } > > EXPORT_SYMBOL_GPL(handle_mm_fault); > > Just a nit, likely not important: I wonder if it would be cleaner to pass > the vm_fault_t into mm_account_fault() and then do the VM_FAULT_RETRY and > VM_FAULT_ERROR checks there as well as putting the comment about how > accounting is handled in that function. Your comment is great. Yes that seems to be cleaner so handle_mm_fault is shorter (btw, I "stole" the comment block majorly from Linus :). But this change will also need to touch patch 25 again or it won't apply cleanly. So I think I'll see whether Andrew would like me to repost the whole series then I'll adopt the change when I repost, or another alternative is maybe we can also do that on top, depending on whether there's further comments.. Thanks! -- Peter Xu
