Re: [RFC PATCH 16/20] famfs: Add fault counters

Dan Williams
2024-02-24T04:30:26Z

Matthew Wilcox wrote:
> On Fri, Feb 23, 2024 at 03:50:33PM -0800, Dan Williams wrote:
> > Certainly something like that would have satisified this sanity test use
> > case. I will note that mm_account_fault() would need some help to figure
> > out the size of the page table entry that got installed. Maybe
> > extensions to vm_fault_reason to add VM_FAULT_P*D? That compliments
> > VM_FAULT_FALLBACK to indicate whether, for example, the fallback went
> > from PUD to PMD, or all the way back to PTE.
>
> ugh, no, it's more complicated than that. look at the recent changes to
> set_ptes(). we can now install PTEs of many different sizes, depending
> on the architecture. someday i look forward to supporting all the page
> sizes on parisc (4k, 16k, 64k, 256k, ... 4G)

Nice!

There are enough bits in vm_fault_t to represent many page sizes instead
of the entry type as I suggested, but I would defer to you or Dave on
how to make "installed pte size" generically traceable per Dave's
suggestion.