The patch titled
Subject: mm/memory: optimize unmap/zap with PTE-mapped THP
has been added to the -mm mm-unstable branch. Its filename is
mm-memory-optimize-unmap-zap-with-pte-mapped-thp.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-memory-optimize-unmap-zap-with-pte-mapped-thp.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
b) Prefer to cc a suitable mailing list as well
c) Ideally: find the original patch on the mailing list and do a
reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next via the mm-everything
branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there every 2-3 working days
------------------------------------------------------
From: David Hildenbrand <david@xxxxxxxxxx>
Subject: mm/memory: optimize unmap/zap with PTE-mapped THP
Date: Wed, 14 Feb 2024 21:44:35 +0100
Similar to how we optimized fork(), let's implement PTE batching when
consecutive (present) PTEs map consecutive pages of the same large folio.
Most infrastructure we need for batching (mmu gather, rmap) is already
there. We only have to add get_and_clear_full_ptes() and
clear_full_ptes(). Similarly, extend zap_install_uffd_wp_if_needed() to
process a PTE range.
We won't bother sanity-checking the mapcount of all subpages, but only
check the mapcount of the first subpage we process. If there is a real
problem hiding somewhere, we can trigger it simply by using small folios,
or when we zap single pages of a large folio. Ideally, we had that check
in rmap code (including for delayed rmap), but then we cannot print the
PTE. Let's keep it simple for now. If we ever have a cheap
folio_mapcount(), we might just want to check for underflows there.
To keep small folios as fast as possible force inlining of a specialized
variant using __always_inline with nr=1.
Link: https://lkml.kernel.org/r/20240214204435.167852-11-david@xxxxxxxxxx
Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
Reviewed-by: Ryan Roberts <ryan.roberts@xxxxxxx>
Cc: Alexander Gordeev <agordeev@xxxxxxxxxxxxx>
Cc: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxx>
Cc: Arnd Bergmann <arnd@xxxxxxxx>
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Christian Borntraeger <borntraeger@xxxxxxxxxxxxx>
Cc: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
Cc: Heiko Carstens <hca@xxxxxxxxxxxxx>
Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: "Naveen N. Rao" <naveen.n.rao@xxxxxxxxxxxxx>
Cc: Nicholas Piggin <npiggin@xxxxxxxxx>
Cc: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: Sven Schnelle <svens@xxxxxxxxxxxxx>
Cc: Vasily Gorbik <gor@xxxxxxxxxxxxx>
Cc: Will Deacon <will@xxxxxxxxxx>
Cc: Yin Fengwei <fengwei.yin@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/pgtable.h | 70 ++++++++++++++++++++++++++++
mm/memory.c | 92 +++++++++++++++++++++++++++-----------
2 files changed, 136 insertions(+), 26 deletions(-)
--- a/include/linux/pgtable.h~mm-memory-optimize-unmap-zap-with-pte-mapped-thp
+++ a/include/linux/pgtable.h
@@ -580,6 +580,76 @@ static inline pte_t ptep_get_and_clear_f
}
#endif
+#ifndef get_and_clear_full_ptes
+/**
+ * get_and_clear_full_ptes - Clear present PTEs that map consecutive pages of
+ * the same folio, collecting dirty/accessed bits.
+ * @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 clear.
+ * @full: Whether we are clearing a full mm.
+ *
+ * May be overridden by the architecture; otherwise, implemented as a simple
+ * loop over ptep_get_and_clear_full(), merging dirty/accessed bits into the
+ * returned PTE.
+ *
+ * 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.
+ */
+static inline pte_t get_and_clear_full_ptes(struct mm_struct *mm,
+ unsigned long addr, pte_t *ptep, unsigned int nr, int full)
+{
+ pte_t pte, tmp_pte;
+
+ pte = ptep_get_and_clear_full(mm, addr, ptep, full);
+ while (--nr) {
+ ptep++;
+ addr += PAGE_SIZE;
+ tmp_pte = ptep_get_and_clear_full(mm, addr, ptep, full);
+ if (pte_dirty(tmp_pte))
+ pte = pte_mkdirty(pte);
+ if (pte_young(tmp_pte))
+ pte = pte_mkyoung(pte);
+ }
+ return pte;
+}
+#endif
+
+#ifndef clear_full_ptes
+/**
+ * clear_full_ptes - Clear present 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 clear.
+ * @full: Whether we are clearing a full mm.
+ *
+ * May be overridden by the architecture; otherwise, implemented as a simple
+ * loop over ptep_get_and_clear_full().
+ *
+ * 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.
+ */
+static inline void clear_full_ptes(struct mm_struct *mm, unsigned long addr,
+ pte_t *ptep, unsigned int nr, int full)
+{
+ for (;;) {
+ ptep_get_and_clear_full(mm, addr, ptep, full);
+ if (--nr == 0)
+ break;
+ ptep++;
+ addr += PAGE_SIZE;
+ }
+}
+#endif
/*
* If two threads concurrently fault at the same page, the thread that
--- a/mm/memory.c~mm-memory-optimize-unmap-zap-with-pte-mapped-thp
+++ a/mm/memory.c
@@ -1515,7 +1515,7 @@ static inline bool zap_drop_file_uffd_wp
*/
static inline void
zap_install_uffd_wp_if_needed(struct vm_area_struct *vma,
- unsigned long addr, pte_t *pte,
+ unsigned long addr, pte_t *pte, int nr,
struct zap_details *details, pte_t pteval)
{
/* Zap on anonymous always means dropping everything */
@@ -1525,20 +1525,27 @@ zap_install_uffd_wp_if_needed(struct vm_
if (zap_drop_file_uffd_wp(details))
return;
- pte_install_uffd_wp_if_needed(vma, addr, pte, pteval);
+ for (;;) {
+ /* the PFN in the PTE is irrelevant. */
+ pte_install_uffd_wp_if_needed(vma, addr, pte, pteval);
+ if (--nr == 0)
+ break;
+ pte++;
+ addr += PAGE_SIZE;
+ }
}
-static inline void zap_present_folio_pte(struct mmu_gather *tlb,
+static __always_inline void zap_present_folio_ptes(struct mmu_gather *tlb,
struct vm_area_struct *vma, struct folio *folio,
- struct page *page, pte_t *pte, pte_t ptent, unsigned long addr,
- struct zap_details *details, int *rss, bool *force_flush,
- bool *force_break)
+ struct page *page, pte_t *pte, pte_t ptent, unsigned int nr,
+ unsigned long addr, struct zap_details *details, int *rss,
+ bool *force_flush, bool *force_break)
{
struct mm_struct *mm = tlb->mm;
bool delay_rmap = false;
if (!folio_test_anon(folio)) {
- ptent = ptep_get_and_clear_full(mm, addr, pte, tlb->fullmm);
+ ptent = get_and_clear_full_ptes(mm, addr, pte, nr, tlb->fullmm);
if (pte_dirty(ptent)) {
folio_mark_dirty(folio);
if (tlb_delay_rmap(tlb)) {
@@ -1548,36 +1555,49 @@ static inline void zap_present_folio_pte
}
if (pte_young(ptent) && likely(vma_has_recency(vma)))
folio_mark_accessed(folio);
- rss[mm_counter(folio)]--;
+ rss[mm_counter(folio)] -= nr;
} else {
/* We don't need up-to-date accessed/dirty bits. */
- ptep_get_and_clear_full(mm, addr, pte, tlb->fullmm);
- rss[MM_ANONPAGES]--;
+ clear_full_ptes(mm, addr, pte, nr, tlb->fullmm);
+ rss[MM_ANONPAGES] -= nr;
}
+ /* Checking a single PTE in a batch is sufficient. */
arch_check_zapped_pte(vma, ptent);
- tlb_remove_tlb_entry(tlb, pte, addr);
+ tlb_remove_tlb_entries(tlb, pte, nr, addr);
if (unlikely(userfaultfd_pte_wp(vma, ptent)))
- zap_install_uffd_wp_if_needed(vma, addr, pte, details, ptent);
+ zap_install_uffd_wp_if_needed(vma, addr, pte, nr, details,
+ ptent);
if (!delay_rmap) {
- folio_remove_rmap_pte(folio, page, vma);
+ folio_remove_rmap_ptes(folio, page, nr, vma);
+
+ /* Only sanity-check the first page in a batch. */
if (unlikely(page_mapcount(page) < 0))
print_bad_pte(vma, addr, ptent, page);
}
- if (unlikely(__tlb_remove_page(tlb, page, delay_rmap))) {
+ if (unlikely(__tlb_remove_folio_pages(tlb, page, nr, delay_rmap))) {
*force_flush = true;
*force_break = true;
}
}
-static inline void zap_present_pte(struct mmu_gather *tlb,
+/*
+ * Zap or skip at least one present PTE, trying to batch-process subsequent
+ * PTEs that map consecutive pages of the same folio.
+ *
+ * Returns the number of processed (skipped or zapped) PTEs (at least 1).
+ */
+static inline int zap_present_ptes(struct mmu_gather *tlb,
struct vm_area_struct *vma, pte_t *pte, pte_t ptent,
- unsigned long addr, struct zap_details *details,
- int *rss, bool *force_flush, bool *force_break)
+ unsigned int max_nr, unsigned long addr,
+ struct zap_details *details, int *rss, bool *force_flush,
+ bool *force_break)
{
+ const fpb_t fpb_flags = FPB_IGNORE_DIRTY | FPB_IGNORE_SOFT_DIRTY;
struct mm_struct *mm = tlb->mm;
struct folio *folio;
struct page *page;
+ int nr;
page = vm_normal_page(vma, addr, ptent);
if (!page) {
@@ -1587,14 +1607,29 @@ static inline void zap_present_pte(struc
tlb_remove_tlb_entry(tlb, pte, addr);
VM_WARN_ON_ONCE(userfaultfd_wp(vma));
ksm_might_unmap_zero_page(mm, ptent);
- return;
+ return 1;
}
folio = page_folio(page);
if (unlikely(!should_zap_folio(details, folio)))
- return;
- zap_present_folio_pte(tlb, vma, folio, page, pte, ptent, addr, details,
- rss, force_flush, force_break);
+ return 1;
+
+ /*
+ * Make sure that the common "small folio" case is as fast as possible
+ * by keeping the batching logic separate.
+ */
+ if (unlikely(folio_test_large(folio) && max_nr != 1)) {
+ nr = folio_pte_batch(folio, addr, pte, ptent, max_nr, fpb_flags,
+ NULL);
+
+ zap_present_folio_ptes(tlb, vma, folio, page, pte, ptent, nr,
+ addr, details, rss, force_flush,
+ force_break);
+ return nr;
+ }
+ zap_present_folio_ptes(tlb, vma, folio, page, pte, ptent, 1, addr,
+ details, rss, force_flush, force_break);
+ return 1;
}
static unsigned long zap_pte_range(struct mmu_gather *tlb,
@@ -1609,6 +1644,7 @@ static unsigned long zap_pte_range(struc
pte_t *start_pte;
pte_t *pte;
swp_entry_t entry;
+ int nr;
tlb_change_page_size(tlb, PAGE_SIZE);
init_rss_vec(rss);
@@ -1622,7 +1658,9 @@ static unsigned long zap_pte_range(struc
pte_t ptent = ptep_get(pte);
struct folio *folio;
struct page *page;
+ int max_nr;
+ nr = 1;
if (pte_none(ptent))
continue;
@@ -1630,10 +1668,12 @@ static unsigned long zap_pte_range(struc
break;
if (pte_present(ptent)) {
- zap_present_pte(tlb, vma, pte, ptent, addr, details,
- rss, &force_flush, &force_break);
+ max_nr = (end - addr) / PAGE_SIZE;
+ nr = zap_present_ptes(tlb, vma, pte, ptent, max_nr,
+ addr, details, rss, &force_flush,
+ &force_break);
if (unlikely(force_break)) {
- addr += PAGE_SIZE;
+ addr += nr * PAGE_SIZE;
break;
}
continue;
@@ -1687,8 +1727,8 @@ static unsigned long zap_pte_range(struc
WARN_ON_ONCE(1);
}
pte_clear_not_present_full(mm, addr, pte, tlb->fullmm);
- zap_install_uffd_wp_if_needed(vma, addr, pte, details, ptent);
- } while (pte++, addr += PAGE_SIZE, addr != end);
+ zap_install_uffd_wp_if_needed(vma, addr, pte, 1, details, ptent);
+ } while (pte += nr, addr += PAGE_SIZE * nr, addr != end);
add_mm_rss_vec(mm, rss);
arch_leave_lazy_mmu_mode();
_
Patches currently in -mm which might be from david@xxxxxxxxxx are
arm-pgtable-define-pfn_pte_shift.patch
nios2-pgtable-define-pfn_pte_shift.patch
powerpc-pgtable-define-pfn_pte_shift.patch
riscv-pgtable-define-pfn_pte_shift.patch
s390-pgtable-define-pfn_pte_shift.patch
sparc-pgtable-define-pfn_pte_shift.patch
mm-pgtable-make-pte_next_pfn-independent-of-set_ptes.patch
arm-mm-use-pte_next_pfn-in-set_ptes.patch
powerpc-mm-use-pte_next_pfn-in-set_ptes.patch
mm-memory-factor-out-copying-the-actual-pte-in-copy_present_pte.patch
mm-memory-pass-pte-to-copy_present_pte.patch
mm-memory-optimize-fork-with-pte-mapped-thp.patch
mm-memory-ignore-dirty-accessed-soft-dirty-bits-in-folio_pte_batch.patch
mm-memory-ignore-writable-bit-in-folio_pte_batch.patch
mm-memory-factor-out-zapping-of-present-pte-into-zap_present_pte.patch
mm-memory-handle-page-case-in-zap_present_pte-separately.patch
mm-memory-further-separate-anon-and-pagecache-folio-handling-in-zap_present_pte.patch
mm-memory-factor-out-zapping-folio-pte-into-zap_present_folio_pte.patch
mm-mmu_gather-pass-delay_rmap-instead-of-encoded-page-to-__tlb_remove_page_size.patch
mm-mmu_gather-define-encoded_page_flag_delay_rmap.patch
mm-mmu_gather-add-tlb_remove_tlb_entries.patch
mm-mmu_gather-add-__tlb_remove_folio_pages.patch
mm-mmu_gather-improve-cond_resched-handling-with-large-folios-and-expensive-page-freeing.patch
mm-memory-optimize-unmap-zap-with-pte-mapped-thp.patch
