This patch optimizes lazyfreeing with PTE-mapped mTHP[1]
(Inspired by David Hildenbrand[2]). We aim to avoid unnecessary
folio splitting if the large folio is entirely within the given
range.
On an Intel I5 CPU, lazyfreeing a 1GiB VMA backed by
PTE-mapped folios of the same size results in the following
runtimes for madvise(MADV_FREE) in seconds (shorter is better):
Folio Size | Old | New | Change
------------------------------------------
4KiB | 0.590251 | 0.590259 | 0%
16KiB | 2.990447 | 0.185655 | -94%
32KiB | 2.547831 | 0.104870 | -95%
64KiB | 2.457796 | 0.052812 | -97%
128KiB | 2.281034 | 0.032777 | -99%
256KiB | 2.230387 | 0.017496 | -99%
512KiB | 2.189106 | 0.010781 | -99%
1024KiB | 2.183949 | 0.007753 | -99%
2048KiB | 0.002799 | 0.002804 | 0%
[1] https://lkml.kernel.org/r/20231207161211.2374093-5-ryan.roberts@xxxxxxx
[2] https://lore.kernel.org/linux-mm/20240214204435.167852-1-david@xxxxxxxxxx
Signed-off-by: Lance Yang <ioworker0@xxxxxxxxx>
---
This patch is rebased on Ryan's patchset[3] and follows a similar pattern to
madvise_cold_or_pageout_pte_range() for madvise_free_pte_range().
[3] https://lore.kernel.org/linux-mm/20240311150058.1122862-1-ryan.roberts@xxxxxxx
The performance numbers are from v2. I did a quick benchmark run of v3 and
nothing significantly changed.
v2 -> v3:
* Only skip all the PTEs for nr_pages when the number of batched PTEs matches
nr_pages per Barry Song
* Change folio_pte_batch() to consume an optional *any_dirty and *any_young
function, per David Hildenbrand
* Move the ptep_get_and_clear_full() loop into refresh_full_ptes(), per
David Hildenbrand
* Follow a similar pattern for madvise_free_pte_range(), per Ryan Roberts
* https://lore.kernel.org/linux-mm/20240307061425.21013-1-ioworker0@xxxxxxxxx
v1 -> v2:
* Update the performance numbers
* Update the changelog, suggested by Ryan Roberts
* Check the COW folio, suggested by Yin Fengwei
* Check if we are mapping all subpages, suggested by Barry Song,
David Hildenbrand, Ryan Roberts
* https://lore.kernel.org/linux-mm/20240225123215.86503-1-ioworker0@xxxxxxxxx
include/linux/pgtable.h | 48 ++++++++++++
mm/internal.h | 17 ++++-
mm/madvise.c | 159 +++++++++++++++++++++-------------------
mm/memory.c | 4 +-
4 files changed, 149 insertions(+), 79 deletions(-)
diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
index 8cf1f2fe2c25..3ca9ae29e653 100644
--- a/include/linux/pgtable.h
+++ b/include/linux/pgtable.h
@@ -736,6 +736,54 @@ static inline void clear_not_present_full_ptes(struct mm_struct *mm,
}
#endif
+/* Flags for refresh_full_ptes(). */
+typedef int __bitwise rfp_t;
+
+/* Refresh PTEs after pte_mkold(), droping the accessed bit. */
+#define RFP_CLEAR_YOUNG ((__force rfp_t)BIT(0))
+
+/* Refresh PTEs after pte_mkclean(), droping the dirty bit. */
+#define RFP_CLEAR_DIRTY ((__force rfp_t)BIT(1))
+
+/**
+ * refresh_full_ptes - refresh 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 refresh.
+ * @flags: Flags to indicate the PTE refresh semantics.
+ * @full: Whether we are clearing a full mm.
+ *
+ * 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 refresh_full_ptes(struct mm_struct *mm, unsigned long addr,
+ pte_t *ptep, unsigned int nr, rfp_t flags, int full)
+{
+ pte_t ptent;
+
+ for (;;) {
+ ptent = ptep_get_and_clear_full(mm, addr, ptep, full);
+
+ if (flags & RFP_CLEAR_YOUNG)
+ ptent = pte_mkold(ptent);
+
+ if (flags & RFP_CLEAR_DIRTY)
+ ptent = pte_mkclean(ptent);
+
+ set_pte_at(mm, addr, ptep, ptent);
+
+ if (--nr == 0)
+ break;
+ ptep++;
+ addr += PAGE_SIZE;
+ }
+}
+
#ifndef __HAVE_ARCH_PTEP_CLEAR_FLUSH
extern pte_t ptep_clear_flush(struct vm_area_struct *vma,
unsigned long address,
diff --git a/mm/internal.h b/mm/internal.h
index 9256d440a080..3610f2f65f8e 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -130,16 +130,20 @@ static inline pte_t __pte_batch_clear_ignored(pte_t pte, fpb_t flags)
*/
static inline int folio_pte_batch(struct folio *folio, unsigned long addr,
pte_t *start_ptep, pte_t pte, int max_nr, fpb_t flags,
- bool *any_writable)
+ bool *any_writable, bool *any_young, bool *any_dirty)
{
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, *ptep;
- bool writable;
+ bool writable, young, dirty;
int nr;
if (any_writable)
*any_writable = false;
+ if (any_young)
+ *any_young = false;
+ if (any_dirty)
+ *any_dirty = false;
VM_WARN_ON_FOLIO(!pte_present(pte), folio);
VM_WARN_ON_FOLIO(!folio_test_large(folio) || max_nr < 1, folio);
@@ -153,6 +157,11 @@ static inline int folio_pte_batch(struct folio *folio, unsigned long addr,
pte = ptep_get(ptep);
if (any_writable)
writable = !!pte_write(pte);
+ if (any_young)
+ young = !!pte_young(pte);
+ if (any_dirty)
+ dirty = !!pte_dirty(pte);
+
pte = __pte_batch_clear_ignored(pte, flags);
if (!pte_same(pte, expected_pte))
@@ -168,6 +177,10 @@ static inline int folio_pte_batch(struct folio *folio, unsigned long addr,
if (any_writable)
*any_writable |= writable;
+ if (any_young)
+ *any_young |= young;
+ if (any_dirty)
+ *any_dirty |= dirty;
nr = pte_batch_hint(ptep, pte);
expected_pte = pte_advance_pfn(expected_pte, nr);
diff --git a/mm/madvise.c b/mm/madvise.c
index 56c7ba7bd558..f88b4d7d75cb 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -321,6 +321,38 @@ static inline bool can_do_file_pageout(struct vm_area_struct *vma)
file_permission(vma->vm_file, MAY_WRITE) == 0;
}
+static inline int madvise_folio_pte_batch(unsigned long addr, unsigned long end,
+ struct folio *folio, pte_t *pte,
+ bool *any_young, bool *any_dirty)
+{
+ int max_nr = (end - addr) / PAGE_SIZE;
+ const fpb_t fpb_flags = FPB_IGNORE_DIRTY | FPB_IGNORE_SOFT_DIRTY;
+
+ return folio_pte_batch(folio, addr, pte, ptep_get(pte), max_nr,
+ fpb_flags, NULL, any_young, any_dirty);
+}
+
+static inline bool madvise_split_folio(struct mm_struct *mm, pmd_t *pmd,
+ unsigned long addr, struct folio *folio,
+ pte_t **pte, spinlock_t **ptl)
+{
+ int err;
+
+ if (!folio_trylock(folio))
+ return false;
+
+ folio_get(folio);
+ pte_unmap_unlock(*pte, *ptl);
+ *pte = NULL;
+ err = split_folio(folio);
+ folio_unlock(folio);
+ folio_put(folio);
+
+ *pte = pte_offset_map_lock(mm, pmd, addr, ptl);
+
+ return err == 0;
+}
+
static int madvise_cold_or_pageout_pte_range(pmd_t *pmd,
unsigned long addr, unsigned long end,
struct mm_walk *walk)
@@ -334,9 +366,10 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *pmd,
spinlock_t *ptl;
struct folio *folio = NULL;
LIST_HEAD(folio_list);
- bool pageout_anon_only_filter;
+ bool pageout_anon_only_filter, any_young;
unsigned int batch_count = 0;
int nr;
+ const rfp_t rfp_flags = RFP_CLEAR_YOUNG;
if (fatal_signal_pending(current))
return -EINTR;
@@ -456,39 +489,25 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *pmd,
* next pte in the range.
*/
if (folio_test_large(folio)) {
- const fpb_t fpb_flags = FPB_IGNORE_DIRTY |
- FPB_IGNORE_SOFT_DIRTY;
- int max_nr = (end - addr) / PAGE_SIZE;
-
- nr = folio_pte_batch(folio, addr, pte, ptent, max_nr,
- fpb_flags, NULL);
-
+ nr = madvise_folio_pte_batch(addr, end, folio, pte,
+ &any_young, NULL);
+ if (folio_estimated_sharers(folio) > 1)
+ continue;
if (nr < folio_nr_pages(folio)) {
- int err;
-
- if (folio_estimated_sharers(folio) > 1)
- continue;
if (pageout_anon_only_filter && !folio_test_anon(folio))
continue;
- if (!folio_trylock(folio))
- continue;
- folio_get(folio);
arch_leave_lazy_mmu_mode();
- pte_unmap_unlock(start_pte, ptl);
- start_pte = NULL;
- err = split_folio(folio);
- folio_unlock(folio);
- folio_put(folio);
- if (err)
- continue;
- start_pte = pte =
- pte_offset_map_lock(mm, pmd, addr, &ptl);
+ if (madvise_split_folio(mm, pmd, addr, folio,
+ &start_pte, &ptl))
+ nr = 0;
if (!start_pte)
break;
+ pte = start_pte;
arch_enter_lazy_mmu_mode();
- nr = 0;
continue;
}
+ if (any_young)
+ ptent = pte_mkyoung(ptent);
}
/*
@@ -504,11 +523,9 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *pmd,
if (pageout_anon_only_filter && !folio_test_anon(folio))
continue;
- if (!pageout) {
- for (; nr != 0; nr--, pte++, addr += PAGE_SIZE) {
- if (ptep_test_and_clear_young(vma, addr, pte))
- tlb_remove_tlb_entry(tlb, pte, addr);
- }
+ if (!pageout && pte_young(ptent)) {
+ refresh_full_ptes(mm, addr, pte, nr, rfp_flags, tlb->fullmm);
+ tlb_remove_tlb_entries(tlb, pte, nr, addr);
}
/*
@@ -642,6 +659,8 @@ static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr,
int nr_swap = 0;
unsigned long next;
int nr, max_nr;
+ bool any_young, any_dirty;
+ const rfp_t rfp_flags = RFP_CLEAR_YOUNG | RFP_CLEAR_DIRTY;
next = pmd_addr_end(addr, end);
if (pmd_trans_huge(*pmd))
@@ -654,7 +673,7 @@ static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr,
return 0;
flush_tlb_batched_pending(mm);
arch_enter_lazy_mmu_mode();
- for (; addr != end; pte += nr, addr += PAGE_SIZE * nr) {
+ for (; addr < end; pte += nr, addr += PAGE_SIZE * nr) {
nr = 1;
ptent = ptep_get(pte);
@@ -687,57 +706,52 @@ static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr,
continue;
/*
- * If pmd isn't transhuge but the folio is large and
- * is owned by only this process, split it and
- * deactivate all pages.
+ * If we encounter a large folio, only split it if it is not
+ * fully mapped within the range we are operating on. Otherwise
+ * leave it as is so that it can be marked as lazyfree. If we
+ * fail to split a folio, leave it in place and advance to the
+ * next pte in the range.
*/
if (folio_test_large(folio)) {
- int err;
+ nr = madvise_folio_pte_batch(addr, end, folio, pte,
+ &any_young, &any_dirty);
+ if (folio_estimated_sharers(folio) > 1)
+ continue;
+ if (nr < folio_nr_pages(folio)) {
+ arch_leave_lazy_mmu_mode();
+ if (madvise_split_folio(mm, pmd, addr, folio,
+ &start_pte, &ptl))
+ nr = 0;
+ if (!start_pte)
+ break;
+ pte = start_pte;
+ arch_enter_lazy_mmu_mode();
+ continue;
+ }
+ if (any_young || any_dirty)
+ ptent = pte_mkyoung(pte_mkdirty(ptent));
+ }
- if (folio_estimated_sharers(folio) != 1)
- break;
- if (!folio_trylock(folio))
- break;
- folio_get(folio);
- arch_leave_lazy_mmu_mode();
- pte_unmap_unlock(start_pte, ptl);
- start_pte = NULL;
- err = split_folio(folio);
+ if (!folio_trylock(folio))
+ continue;
+ /*
+ * If we have a large folio at this point, we know it is fully mapped
+ * so if its mapcount is the same as its number of pages, it must be
+ * exclusive.
+ */
+ if (folio_mapcount(folio) != folio_nr_pages(folio)) {
folio_unlock(folio);
- folio_put(folio);
- if (err)
- break;
- start_pte = pte =
- pte_offset_map_lock(mm, pmd, addr, &ptl);
- if (!start_pte)
- break;
- arch_enter_lazy_mmu_mode();
- pte--;
- addr -= PAGE_SIZE;
continue;
}
-
if (folio_test_swapcache(folio) || folio_test_dirty(folio)) {
- if (!folio_trylock(folio))
- continue;
- /*
- * If folio is shared with others, we mustn't clear
- * the folio's dirty flag.
- */
- if (folio_mapcount(folio) != 1) {
- folio_unlock(folio);
- continue;
- }
-
if (folio_test_swapcache(folio) &&
!folio_free_swap(folio)) {
folio_unlock(folio);
continue;
}
-
folio_clear_dirty(folio);
- folio_unlock(folio);
}
+ folio_unlock(folio);
if (pte_young(ptent) || pte_dirty(ptent)) {
/*
@@ -746,13 +760,8 @@ static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr,
* the portability, remap the pte with old|clean
* after pte clearing.
*/
- ptent = ptep_get_and_clear_full(mm, addr, pte,
- tlb->fullmm);
-
- ptent = pte_mkold(ptent);
- ptent = pte_mkclean(ptent);
- set_pte_at(mm, addr, pte, ptent);
- tlb_remove_tlb_entry(tlb, pte, addr);
+ refresh_full_ptes(mm, addr, pte, nr, rfp_flags, tlb->fullmm);
+ tlb_remove_tlb_entries(tlb, pte, nr, addr);
}
folio_mark_lazyfree(folio);
}
diff --git a/mm/memory.c b/mm/memory.c
index 25c0ef1c7ff3..7121e5cc74d9 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -989,7 +989,7 @@ copy_present_ptes(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma
flags |= FPB_IGNORE_SOFT_DIRTY;
nr = folio_pte_batch(folio, addr, src_pte, pte, max_nr, flags,
- &any_writable);
+ &any_writable, NULL, NULL);
folio_ref_add(folio, nr);
if (folio_test_anon(folio)) {
if (unlikely(folio_try_dup_anon_rmap_ptes(folio, page,
@@ -1551,7 +1551,7 @@ static inline int zap_present_ptes(struct mmu_gather *tlb,
*/
if (unlikely(folio_test_large(folio) && max_nr != 1)) {
nr = folio_pte_batch(folio, addr, pte, ptent, max_nr, fpb_flags,
- NULL);
+ NULL, NULL, NULL);
zap_present_folio_ptes(tlb, vma, folio, page, pte, ptent, nr,
addr, details, rss, force_flush,
--
2.33.1
