The patch titled
Subject: mm/vmscan: avoid split PMD-mapped THP during shrink_folio_list()
has been added to the -mm mm-unstable branch. Its filename is
mm-vmscan-avoid-split-pmd-mapped-thp-during-shrink_folio_list.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-vmscan-avoid-split-pmd-mapped-thp-during-shrink_folio_list.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Lance Yang <ioworker0@xxxxxxxxx>
Subject: mm/vmscan: avoid split PMD-mapped THP during shrink_folio_list()
Date: Mon, 22 Apr 2024 13:52:13 +0800
When the user no longer requires the pages, they would use
madvise(MADV_FREE) to mark the pages as lazy free. IMO, they would not
typically rewrite to the given range.
At present, PMD-mapped THPs that are marked as lazyfree during
shrink_folio_list() are unconditionally split, which may be unnecessary.
If the THP is clean, its PMD is also clean, and there are no unexpected
references, then we can attempt to remove the PMD mapping from it. This
change will improve the efficiency of memory reclamation in this case.
On an Intel i5 CPU, reclaiming 1GiB of PMD-mapped THPs using
mem_cgroup_force_empty() results in the following runtimes in seconds
(shorter is better):
--------------------------------------------
| Old | New | Change |
--------------------------------------------
| 0.683426 | 0.049197 | -92.80% |
--------------------------------------------
Link: https://lkml.kernel.org/r/20240422055213.60231-1-ioworker0@xxxxxxxxx
Signed-off-by: Lance Yang <ioworker0@xxxxxxxxx>
Cc: Barry Song <21cnbao@xxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Fangrui Song <maskray@xxxxxxxxxx>
Cc: Jeff Xie <xiehuan09@xxxxxxxxx>
Cc: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>
Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Minchan Kim <minchan@xxxxxxxxxx>
Cc: Muchun Song <songmuchun@xxxxxxxxxxxxx>
Cc: Peter Xu <peterx@xxxxxxxxxx>
Cc: Yang Shi <shy828301@xxxxxxxxx>
Cc: Yin Fengwei <fengwei.yin@xxxxxxxxx>
Cc: Zach O'Keefe <zokeefe@xxxxxxxxxx>
Cc: Zi Yan <ziy@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/huge_mm.h | 2
include/linux/rmap.h | 2
mm/huge_memory.c | 88 ++++++++++++++++++++++++++++++++++++++
mm/rmap.c | 6 ++
mm/vmscan.c | 7 +++
5 files changed, 105 insertions(+)
--- a/include/linux/huge_mm.h~mm-vmscan-avoid-split-pmd-mapped-thp-during-shrink_folio_list
+++ a/include/linux/huge_mm.h
@@ -36,6 +36,8 @@ bool move_huge_pmd(struct vm_area_struct
int change_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
pmd_t *pmd, unsigned long addr, pgprot_t newprot,
unsigned long cp_flags);
+bool discard_trans_pmd(struct vm_area_struct *vma, unsigned long addr,
+ struct folio *folio);
vm_fault_t vmf_insert_pfn_pmd(struct vm_fault *vmf, pfn_t pfn, bool write);
vm_fault_t vmf_insert_pfn_pud(struct vm_fault *vmf, pfn_t pfn, bool write);
--- a/include/linux/rmap.h~mm-vmscan-avoid-split-pmd-mapped-thp-during-shrink_folio_list
+++ a/include/linux/rmap.h
@@ -100,6 +100,8 @@ enum ttu_flags {
* do a final flush if necessary */
TTU_RMAP_LOCKED = 0x80, /* do not grab rmap lock:
* caller holds it */
+ TTU_LAZYFREE_THP = 0x100, /* avoid splitting PMD-mapped THPs
+ * that are marked as lazyfree. */
};
#ifdef CONFIG_MMU
--- a/mm/huge_memory.c~mm-vmscan-avoid-split-pmd-mapped-thp-during-shrink_folio_list
+++ a/mm/huge_memory.c
@@ -1810,6 +1810,94 @@ static inline void zap_deposited_table(s
mm_dec_nr_ptes(mm);
}
+bool discard_trans_pmd(struct vm_area_struct *vma, unsigned long addr,
+ struct folio *folio)
+{
+ struct mm_struct *mm = vma->vm_mm;
+ struct mmu_notifier_range range;
+ int ref_count, map_count;
+ struct mmu_gather tlb;
+ pmd_t *pmdp, orig_pmd;
+ struct page *page;
+ bool ret = false;
+ spinlock_t *ptl;
+
+ VM_WARN_ON_FOLIO(!folio_test_anon(folio), folio);
+ VM_WARN_ON_FOLIO(!folio_test_locked(folio), folio);
+ VM_WARN_ON_FOLIO(folio_test_swapbacked(folio), folio);
+ VM_WARN_ON_FOLIO(!folio_test_pmd_mappable(folio), folio);
+
+ /* Perform best-effort early checks before acquiring the PMD lock */
+ if (folio_ref_count(folio) != folio_mapcount(folio) + 1 ||
+ folio_test_dirty(folio))
+ return false;
+
+ pmdp = mm_find_pmd(mm, addr);
+ if (unlikely(!pmdp))
+ return false;
+ if (pmd_dirty(*pmdp))
+ return false;
+
+ tlb_gather_mmu(&tlb, mm);
+ mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, mm,
+ addr & HPAGE_PMD_MASK,
+ (addr & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE);
+ mmu_notifier_invalidate_range_start(&range);
+
+ ptl = pmd_lock(mm, pmdp);
+ orig_pmd = *pmdp;
+ if (unlikely(!pmd_present(orig_pmd) || !pmd_trans_huge(orig_pmd)))
+ goto out;
+
+ page = pmd_page(orig_pmd);
+ if (unlikely(page_folio(page) != folio))
+ goto out;
+
+ orig_pmd = pmdp_huge_get_and_clear(mm, addr, pmdp);
+ tlb_remove_pmd_tlb_entry(&tlb, pmdp, addr);
+
+ /*
+ * Syncing against concurrent GUP-fast:
+ * - clear PMD; barrier; read refcount
+ * - inc refcount; barrier; read PMD
+ */
+ smp_mb();
+
+ ref_count = folio_ref_count(folio);
+ map_count = folio_mapcount(folio);
+
+ /*
+ * Order reads for folio refcount and dirty flag
+ * (see comments in __remove_mapping()).
+ */
+ smp_rmb();
+
+ /*
+ * If the PMD or folio is redirtied at this point, or if there are
+ * unexpected references, we will give up to discard this folio
+ * and remap it.
+ *
+ * The only folio refs must be one from isolation plus the rmap(s).
+ */
+ if (ref_count != map_count + 1 || folio_test_dirty(folio) ||
+ pmd_dirty(orig_pmd)) {
+ set_pmd_at(mm, addr, pmdp, orig_pmd);
+ goto out;
+ }
+
+ folio_remove_rmap_pmd(folio, page, vma);
+ zap_deposited_table(mm, pmdp);
+ add_mm_counter(mm, MM_ANONPAGES, -HPAGE_PMD_NR);
+ folio_put(folio);
+ ret = true;
+
+out:
+ spin_unlock(ptl);
+ mmu_notifier_invalidate_range_end(&range);
+
+ return ret;
+}
+
int zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
pmd_t *pmd, unsigned long addr)
{
--- a/mm/rmap.c~mm-vmscan-avoid-split-pmd-mapped-thp-during-shrink_folio_list
+++ a/mm/rmap.c
@@ -1631,6 +1631,12 @@ static bool try_to_unmap_one(struct foli
if (flags & TTU_SYNC)
pvmw.flags = PVMW_SYNC;
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+ if (flags & TTU_LAZYFREE_THP)
+ if (discard_trans_pmd(vma, address, folio))
+ return true;
+#endif
+
if (flags & TTU_SPLIT_HUGE_PMD)
split_huge_pmd_address(vma, address, false, folio);
--- a/mm/vmscan.c~mm-vmscan-avoid-split-pmd-mapped-thp-during-shrink_folio_list
+++ a/mm/vmscan.c
@@ -1260,6 +1260,13 @@ retry:
if (folio_test_pmd_mappable(folio))
flags |= TTU_SPLIT_HUGE_PMD;
+
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+ if (folio_test_anon(folio) && !was_swapbacked &&
+ (flags & TTU_SPLIT_HUGE_PMD))
+ flags |= TTU_LAZYFREE_THP;
+#endif
+
/*
* Without TTU_SYNC, try_to_unmap will only begin to
* hold PTL from the first present PTE within a large
_
Patches currently in -mm which might be from ioworker0@xxxxxxxxx are
mm-madvise-introduce-clear_young_dirty_ptes-batch-helper.patch
mm-arm64-override-clear_young_dirty_ptes-batch-helper.patch
mm-memory-add-any_dirty-optional-pointer-to-folio_pte_batch.patch
mm-madvise-optimize-lazyfreeing-with-mthp-in-madvise_free.patch
mm-vmscan-avoid-split-pmd-mapped-thp-during-shrink_folio_list.patch
