Messages in this thread |  | | From | Yu Zhao <> | Date | Sun, 15 Jan 2023 15:46:54 -0700 | Subject | Re: [PATCH v1] mm: multi-gen LRU: reduce repeated scans in rmap |
| |
On Sun, Jan 15, 2023 at 5:57 AM Jinyu Tang <tjytimi@163.com> wrote: > > The folio is physically and virtually contiguous. If a folio have > more than one pages, lru_gen_look_around() will run several times in > the while loop in folio_referenced_one(), but most of times is > unnecessary. Because these pages always belong to the same pmd and > vma, lru_gen_look_around() will scan the same range.
Thanks -- the commit message is quite clear, so I think I understand what you're thinking.
Let me clarify: 1. First of all, there are no repeated scans, because after lru_gen_look_around() clears the A-bit in a range, the pte_young() test stops it from going into the same range again. 2. Of course, pte_young() can become true later, but this is not a problem because it's cache hot. 3. Physically and virtually contiguous mapping existed before folios: a THP can be mapped by 512 PTEs.
> while (page_vma_mapped_walk(&pvmw)) { > address = pvmw.address; > @@ -825,7 +826,13 @@ static bool folio_referenced_one(struct folio *folio, > if (pvmw.pte) { > if (lru_gen_enabled() && pte_young(*pvmw.pte) && > !(vma->vm_flags & (VM_SEQ_READ | VM_RAND_READ))) { > - lru_gen_look_around(&pvmw); > + unsigned long pmd_now = pvmw.address & PMD_MASK; > + unsigned long pmd_former = former_address & PMD_MASK; > + > + if ((!former_address) || (pmd_now != pmd_former)) { > + lru_gen_look_around(&pvmw); > + former_address = pvmw.address; > + } > referenced++; > }
|  |