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Message-ID: <dde5a9135710d8d883e30e0acadcbf1ae754bf7a.1763976541.git.baolin.wang@linux.alibaba.com>
Date: Tue, 25 Nov 2025 08:56:51 +0800
From: Baolin Wang <baolin.wang@...ux.alibaba.com>
To: akpm@...ux-foundation.org,
david@...nel.org,
catalin.marinas@....com,
will@...nel.org
Cc: lorenzo.stoakes@...cle.com,
ryan.roberts@....com,
Liam.Howlett@...cle.com,
vbabka@...e.cz,
rppt@...nel.org,
surenb@...gle.com,
mhocko@...e.com,
riel@...riel.com,
harry.yoo@...cle.com,
jannh@...gle.com,
willy@...radead.org,
baohua@...nel.org,
baolin.wang@...ux.alibaba.com,
linux-mm@...ck.org,
linux-arm-kernel@...ts.infradead.org,
linux-kernel@...r.kernel.org
Subject: [PATCH 2/2] mm: rmap: support batched checks of the references for large folios
Currently, folio_referenced_one() always checks the young flag for each PTE
sequentially, which is inefficient for large folios. This inefficiency is
especially noticeable when reclaiming clean file-backed large folios, where
folio_referenced() is observed as a significant performance hotspot.
Moreover, on Arm architecture, which supports contiguous PTEs, there is already
an optimization to clear the young flags for PTEs within a contiguous range.
However, this is not sufficient. We can extend this to perform batched operations
for the entire large folio (which might exceed the contiguous range: CONT_PTE_SIZE).
Introduce a new API: clear_flush_young_ptes() to facilitate batched checking
of the young flags and flushing TLB entries, thereby improving performance
during large folio reclamation.
Performance testing:
Allocate 10G clean file-backed folios by mmap() in a memory cgroup, and try to
reclaim 8G file-backed folios via the memory.reclaim interface. I can observe
33% performance improvement on my Arm64 32-core server (and 10%+ improvement
on my X86 machine). Meanwhile, the hotspot folio_check_references() dropped
from approximately 35% to around 5%.
W/o patchset:
real 0m1.518s
user 0m0.000s
sys 0m1.518s
W/ patchset:
real 0m1.018s
user 0m0.000s
sys 0m1.018s
Signed-off-by: Baolin Wang <baolin.wang@...ux.alibaba.com>
---
arch/arm64/include/asm/pgtable.h | 11 +++++++++++
include/linux/mmu_notifier.h | 9 +++++----
include/linux/pgtable.h | 19 +++++++++++++++++++
mm/rmap.c | 22 ++++++++++++++++++++--
4 files changed, 55 insertions(+), 6 deletions(-)
diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index e03034683156..a865bd8c46a3 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -1869,6 +1869,17 @@ static inline int ptep_clear_flush_young(struct vm_area_struct *vma,
return contpte_clear_flush_young_ptes(vma, addr, ptep, CONT_PTES);
}
+#define clear_flush_young_ptes clear_flush_young_ptes
+static inline int clear_flush_young_ptes(struct vm_area_struct *vma,
+ unsigned long addr, pte_t *ptep,
+ unsigned int nr)
+{
+ if (likely(nr == 1))
+ return __ptep_clear_flush_young(vma, addr, ptep);
+
+ return contpte_clear_flush_young_ptes(vma, addr, ptep, nr);
+}
+
#define wrprotect_ptes wrprotect_ptes
static __always_inline void wrprotect_ptes(struct mm_struct *mm,
unsigned long addr, pte_t *ptep, unsigned int nr)
diff --git a/include/linux/mmu_notifier.h b/include/linux/mmu_notifier.h
index d1094c2d5fb6..be594b274729 100644
--- a/include/linux/mmu_notifier.h
+++ b/include/linux/mmu_notifier.h
@@ -515,16 +515,17 @@ static inline void mmu_notifier_range_init_owner(
range->owner = owner;
}
-#define ptep_clear_flush_young_notify(__vma, __address, __ptep) \
+#define ptep_clear_flush_young_notify(__vma, __address, __ptep, __nr) \
({ \
int __young; \
struct vm_area_struct *___vma = __vma; \
unsigned long ___address = __address; \
- __young = ptep_clear_flush_young(___vma, ___address, __ptep); \
+ unsigned int ___nr = __nr; \
+ __young = clear_flush_young_ptes(___vma, ___address, __ptep, ___nr); \
__young |= mmu_notifier_clear_flush_young(___vma->vm_mm, \
___address, \
___address + \
- PAGE_SIZE); \
+ nr * PAGE_SIZE); \
__young; \
})
@@ -650,7 +651,7 @@ static inline void mmu_notifier_subscriptions_destroy(struct mm_struct *mm)
#define mmu_notifier_range_update_to_read_only(r) false
-#define ptep_clear_flush_young_notify ptep_clear_flush_young
+#define ptep_clear_flush_young_notify clear_flush_young_ptes
#define pmdp_clear_flush_young_notify pmdp_clear_flush_young
#define ptep_clear_young_notify ptep_test_and_clear_young
#define pmdp_clear_young_notify pmdp_test_and_clear_young
diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
index b13b6f42be3c..c7d0fd228cb7 100644
--- a/include/linux/pgtable.h
+++ b/include/linux/pgtable.h
@@ -947,6 +947,25 @@ static inline void wrprotect_ptes(struct mm_struct *mm, unsigned long addr,
}
#endif
+#ifndef clear_flush_young_ptes
+static inline int clear_flush_young_ptes(struct vm_area_struct *vma,
+ unsigned long addr, pte_t *ptep,
+ unsigned int nr)
+{
+ int young = 0;
+
+ for (;;) {
+ young |= ptep_clear_flush_young(vma, addr, ptep);
+ if (--nr == 0)
+ break;
+ ptep++;
+ addr += PAGE_SIZE;
+ }
+
+ return young;
+}
+#endif
+
/*
* On some architectures hardware does not set page access bit when accessing
* memory page, it is responsibility of software setting this bit. It brings
diff --git a/mm/rmap.c b/mm/rmap.c
index f955f02d570e..3833b8557a6f 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -827,9 +827,11 @@ static bool folio_referenced_one(struct folio *folio,
struct folio_referenced_arg *pra = arg;
DEFINE_FOLIO_VMA_WALK(pvmw, folio, vma, address, 0);
int ptes = 0, referenced = 0;
+ unsigned int nr;
while (page_vma_mapped_walk(&pvmw)) {
address = pvmw.address;
+ nr = 1;
if (vma->vm_flags & VM_LOCKED) {
ptes++;
@@ -874,9 +876,21 @@ static bool folio_referenced_one(struct folio *folio,
if (lru_gen_look_around(&pvmw))
referenced++;
} else if (pvmw.pte) {
+ if (folio_test_large(folio)) {
+ unsigned long end_addr = pmd_addr_end(address, vma->vm_end);
+ unsigned int max_nr = (end_addr - address) >> PAGE_SHIFT;
+ pte_t pteval = ptep_get(pvmw.pte);
+
+ nr = folio_pte_batch(folio, pvmw.pte, pteval, max_nr);
+ }
+
+ ptes += nr;
if (ptep_clear_flush_young_notify(vma, address,
- pvmw.pte))
+ pvmw.pte, nr))
referenced++;
+ /* Skip the batched PTEs */
+ pvmw.pte += nr - 1;
+ pvmw.address += (nr - 1) * PAGE_SIZE;
} else if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE)) {
if (pmdp_clear_flush_young_notify(vma, address,
pvmw.pmd))
@@ -886,7 +900,11 @@ static bool folio_referenced_one(struct folio *folio,
WARN_ON_ONCE(1);
}
- pra->mapcount--;
+ pra->mapcount -= nr;
+ if (ptes == pvmw.nr_pages) {
+ page_vma_mapped_walk_done(&pvmw);
+ break;
+ }
}
if (referenced)
--
2.47.3
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