From c6ec76a2ebc5829e5826b218d2e1475ec11b333e Mon Sep 17 00:00:00 2001 From: Ryan Roberts Date: Thu, 15 Feb 2024 10:32:02 +0000 Subject: mm: add pte_batch_hint() to reduce scanning in folio_pte_batch() Some architectures (e.g. arm64) can tell from looking at a pte, if some follow-on ptes also map contiguous physical memory with the same pgprot. (for arm64, these are contpte mappings). Take advantage of this knowledge to optimize folio_pte_batch() so that it can skip these ptes when scanning to create a batch. By default, if an arch does not opt-in, folio_pte_batch() returns a compile-time 1, so the changes are optimized out and the behaviour is as before. arm64 will opt-in to providing this hint in the next patch, which will greatly reduce the cost of ptep_get() when scanning a range of contptes. Link: https://lkml.kernel.org/r/20240215103205.2607016-16-ryan.roberts@arm.com Signed-off-by: Ryan Roberts Acked-by: David Hildenbrand Tested-by: John Hubbard Cc: Alistair Popple Cc: Andrey Ryabinin Cc: Ard Biesheuvel Cc: Barry Song <21cnbao@gmail.com> Cc: Borislav Petkov (AMD) Cc: Catalin Marinas Cc: Dave Hansen Cc: "H. Peter Anvin" Cc: Ingo Molnar Cc: James Morse Cc: Kefeng Wang Cc: Marc Zyngier Cc: Mark Rutland Cc: Matthew Wilcox (Oracle) Cc: Thomas Gleixner Cc: Will Deacon Cc: Yang Shi Cc: Zi Yan Signed-off-by: Andrew Morton --- mm/memory.c | 19 ++++++++++++------- 1 file changed, 12 insertions(+), 7 deletions(-) (limited to 'mm/memory.c') diff --git a/mm/memory.c b/mm/memory.c index 465ada39c2b7..642b4f2be523 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -988,16 +988,20 @@ static inline int folio_pte_batch(struct folio *folio, unsigned long addr, { unsigned long folio_end_pfn = folio_pfn(folio) + folio_nr_pages(folio); const pte_t *end_ptep = start_ptep + max_nr; - pte_t expected_pte = __pte_batch_clear_ignored(pte_next_pfn(pte), flags); - pte_t *ptep = start_ptep + 1; + pte_t expected_pte, *ptep; bool writable; + int nr; if (any_writable) *any_writable = false; VM_WARN_ON_FOLIO(!pte_present(pte), folio); - while (ptep != end_ptep) { + nr = pte_batch_hint(start_ptep, pte); + expected_pte = __pte_batch_clear_ignored(pte_advance_pfn(pte, nr), flags); + ptep = start_ptep + nr; + + while (ptep < end_ptep) { pte = ptep_get(ptep); if (any_writable) writable = !!pte_write(pte); @@ -1011,17 +1015,18 @@ static inline int folio_pte_batch(struct folio *folio, unsigned long addr, * corner cases the next PFN might fall into a different * folio. */ - if (pte_pfn(pte) == folio_end_pfn) + if (pte_pfn(pte) >= folio_end_pfn) break; if (any_writable) *any_writable |= writable; - expected_pte = pte_next_pfn(expected_pte); - ptep++; + nr = pte_batch_hint(ptep, pte); + expected_pte = pte_advance_pfn(expected_pte, nr); + ptep += nr; } - return ptep - start_ptep; + return min(ptep - start_ptep, max_nr); } /* -- cgit v1.2.3-70-g09d2