On Thu, Feb 15, 2024 at 10:32:03AM +0000, Ryan Roberts wrote: > When core code iterates over a range of ptes and calls ptep_get() for > each of them, if the range happens to cover contpte mappings, the number > of pte reads becomes amplified by a factor of the number of PTEs in a > contpte block. This is because for each call to ptep_get(), the > implementation must read all of the ptes in the contpte block to which > it belongs to gather the access and dirty bits. > > This causes a hotspot for fork(), as well as operations that unmap > memory such as munmap(), exit and madvise(MADV_DONTNEED). Fortunately we > can fix this by implementing pte_batch_hint() which allows their > iterators to skip getting the contpte tail ptes when gathering the batch > of ptes to operate on. This results in the number of PTE reads returning > to 1 per pte. > > Acked-by: Mark Rutland <mark.rutland@xxxxxxx> > Reviewed-by: David Hildenbrand <david@xxxxxxxxxx> > Tested-by: John Hubbard <jhubbard@xxxxxxxxxx> > Signed-off-by: Ryan Roberts <ryan.roberts@xxxxxxx> Acked-by: Catalin Marinas <catalin.marinas@xxxxxxx>
