On 17 Jul 2023, at 11:51, Ryan Roberts wrote: > On 17/07/2023 16:09, Zi Yan wrote: >> On 17 Jul 2023, at 10:31, Ryan Roberts wrote: >> >>> Like page_remove_rmap() but batch-removes the rmap for a range of pages >>> belonging to a folio. This can provide a small speedup due to less >>> manipuation of the various counters. But more crucially, if removing the >>> rmap for all pages of a folio in a batch, there is no need to >>> (spuriously) add it to the deferred split list, which saves significant >>> cost when there is contention for the split queue lock. >>> >>> All contained pages are accounted using the order-0 folio (or base page) >>> scheme. >>> >>> Signed-off-by: Ryan Roberts <ryan.roberts@xxxxxxx> >>> --- >>> include/linux/rmap.h | 2 ++ >>> mm/rmap.c | 65 ++++++++++++++++++++++++++++++++++++++++++++ >>> 2 files changed, 67 insertions(+) >>> >>> diff --git a/include/linux/rmap.h b/include/linux/rmap.h >>> index b87d01660412..f578975c12c0 100644 >>> --- a/include/linux/rmap.h >>> +++ b/include/linux/rmap.h >>> @@ -200,6 +200,8 @@ void page_add_file_rmap(struct page *, struct vm_area_struct *, >>> bool compound); >>> void page_remove_rmap(struct page *, struct vm_area_struct *, >>> bool compound); >>> +void folio_remove_rmap_range(struct folio *folio, struct page *page, >>> + int nr, struct vm_area_struct *vma); >>> >>> void hugepage_add_anon_rmap(struct page *, struct vm_area_struct *, >>> unsigned long address, rmap_t flags); >>> diff --git a/mm/rmap.c b/mm/rmap.c >>> index 2baf57d65c23..1da05aca2bb1 100644 >>> --- a/mm/rmap.c >>> +++ b/mm/rmap.c >>> @@ -1359,6 +1359,71 @@ void page_add_file_rmap(struct page *page, struct vm_area_struct *vma, >>> mlock_vma_folio(folio, vma, compound); >>> } >>> >>> +/* >>> + * folio_remove_rmap_range - take down pte mappings from a range of pages >>> + * belonging to a folio. All pages are accounted as small pages. >>> + * @folio: folio that all pages belong to >>> + * @page: first page in range to remove mapping from >>> + * @nr: number of pages in range to remove mapping from >> >> We might need some checks to make sure [page, page+nr] is in the range of >> the folio. Something like: >> >> page >= &folio->page && page + nr < (&folio->page + folio_nr_pages(folio)) > > No problem. Is a VM_WARN_ON() appropriate for something like this? VM_WARN_ON_ONCE() might be better. -- Best Regards, Yan, Zi
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