On 25.01.24 20:32, David Hildenbrand wrote:
Let's implement PTE batching when consecutive (present) PTEs map
consecutive pages of the same large folio, and all other PTE bits besides
the PFNs are equal.
We will optimize folio_pte_batch() separately, to ignore selected
PTE bits. This patch is based on work by Ryan Roberts.
Use __always_inline for __copy_present_ptes() and keep the handling for
single PTEs completely separate from the multi-PTE case: we really want
the compiler to optimize for the single-PTE case with small folios, to
not degrade performance.
Note that PTE batching will never exceed a single page table and will
always stay within VMA boundaries.
Further, processing PTE-mapped THP that maybe pinned and have
PageAnonExclusive set on at least one subpage should work as expected,
but there is room for improvement: We will repeatedly (1) detect a PTE
batch (2) detect that we have to copy a page (3) fall back and allocate a
single page to copy a single page. For now we won't care as pinned pages
are a corner case, and we should rather look into maintaining only a
single PageAnonExclusive bit for large folios.
Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
---
include/linux/pgtable.h | 31 +++++++++++
mm/memory.c | 112 +++++++++++++++++++++++++++++++++-------
2 files changed, 124 insertions(+), 19 deletions(-)
diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
index 351cd9dc7194f..891ed246978a4 100644
--- a/include/linux/pgtable.h
+++ b/include/linux/pgtable.h
@@ -650,6 +650,37 @@ static inline void ptep_set_wrprotect(struct mm_struct *mm, unsigned long addres
}
#endif
+#ifndef wrprotect_ptes
+/**
+ * wrprotect_ptes - Write-protect consecutive pages that are mapped to a
+ * contiguous range of addresses.
+ * @mm: Address space to map the pages into.
+ * @addr: Address the first page is mapped at.
+ * @ptep: Page table pointer for the first entry.
+ * @nr: Number of pages to write-protect.
+ *
+ * May be overridden by the architecture; otherwise, implemented as a simple
+ * loop over ptep_set_wrprotect().
+ *
+ * Note that PTE bits in the PTE range besides the PFN can differ. For example,
+ * some PTEs might already be write-protected.
+ *
+ * Context: The caller holds the page table lock. The pages all belong
+ * to the same folio. The PTEs are all in the same PMD.
+ */
After writing documentation for another two such functions, I'll change this to:
/**
* wrprotect_ptes - Write-protect PTEs that map consecutive pages of the same
* folio.
* @mm: Address space the pages are mapped into.
* @addr: Address the first page is mapped at.
* @ptep: Page table pointer for the first entry.
* @nr: Number of entries to write-protect.
*
* May be overridden by the architecture; otherwise, implemented as a simple
* loop over ptep_set_wrprotect().
*
* Note that PTE bits in the PTE range besides the PFN can differ. For example,
* some PTEs might be write-protected.
*
* Context: The caller holds the page table lock. The PTEs map consecutive
* pages that belong to the same folio. The PTEs are all in the same PMD.
*/
--
Cheers,
David / dhildenb
