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Peter Anvin" , Steven Rostedt , Masami Hiramatsu , Mathieu Desnoyers , Shaoqin Huang , Gavin Shan , Ricardo Koller , Raghavendra Rao Ananta , Ryan Roberts , David Rientjes , Axel Rasmussen , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, kvm@vger.kernel.org, linux-mm@kvack.org, linux-trace-kernel@vger.kernel.org, James Houghton Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Yu Zhao Use mmu_notifier_{test,clear}_young_bitmap() to handle KVM PTEs in batches when the fast path is supported. This reduces the contention on kvm->mmu_lock when the host is under heavy memory pressure. An existing selftest can quickly demonstrate the effectiveness of this patch. On a generic workstation equipped with 128 CPUs and 256GB DRAM: $ sudo max_guest_memory_test -c 64 -m 250 -s 250 MGLRU run2 ------------------ Before [1] ~64s After ~51s kswapd (MGLRU before) 100.00% balance_pgdat 100.00% shrink_node 100.00% shrink_one 99.99% try_to_shrink_lruvec 99.71% evict_folios 97.29% shrink_folio_list =3D=3D>> 13.05% folio_referenced 12.83% rmap_walk_file 12.31% folio_referenced_one 7.90% __mmu_notifier_clear_young 7.72% kvm_mmu_notifier_clear_young 7.34% _raw_write_lock kswapd (MGLRU after) 100.00% balance_pgdat 100.00% shrink_node 100.00% shrink_one 99.99% try_to_shrink_lruvec 99.59% evict_folios 80.37% shrink_folio_list =3D=3D>> 3.74% folio_referenced 3.59% rmap_walk_file 3.19% folio_referenced_one 2.53% lru_gen_look_around 1.06% __mmu_notifier_test_clear_young [1] "mm: rmap: Don't flush TLB after checking PTE young for page reference" was included so that the comparison is apples to apples. https://lore.kernel.org/r/20220706112041.3831-1-21cnbao@gmail.com/ Signed-off-by: Yu Zhao Signed-off-by: James Houghton --- Documentation/admin-guide/mm/multigen_lru.rst | 6 +- include/linux/mmzone.h | 6 +- mm/rmap.c | 9 +- mm/vmscan.c | 183 ++++++++++++++---- 4 files changed, 159 insertions(+), 45 deletions(-) diff --git a/Documentation/admin-guide/mm/multigen_lru.rst b/Documentation/= admin-guide/mm/multigen_lru.rst index 33e068830497..0ae2a6d4d94c 100644 --- a/Documentation/admin-guide/mm/multigen_lru.rst +++ b/Documentation/admin-guide/mm/multigen_lru.rst @@ -48,6 +48,10 @@ Values Components verified on x86 varieties other than Intel and AMD. If it is disabled, the multi-gen LRU will suffer a negligible performance degradation. +0x0008 Clearing the accessed bit in KVM page table entries in large + batches, when KVM MMU sets it (e.g., on x86_64). This can + improve the performance of guests when the host is under memory + pressure. [yYnN] Apply to all the components above. =3D=3D=3D=3D=3D=3D =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D =20 @@ -56,7 +60,7 @@ E.g., =20 echo y >/sys/kernel/mm/lru_gen/enabled cat /sys/kernel/mm/lru_gen/enabled - 0x0007 + 0x000f echo 5 >/sys/kernel/mm/lru_gen/enabled cat /sys/kernel/mm/lru_gen/enabled 0x0005 diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h index c11b7cde81ef..a98de5106990 100644 --- a/include/linux/mmzone.h +++ b/include/linux/mmzone.h @@ -397,6 +397,7 @@ enum { LRU_GEN_CORE, LRU_GEN_MM_WALK, LRU_GEN_NONLEAF_YOUNG, + LRU_GEN_KVM_MMU_WALK, NR_LRU_GEN_CAPS }; =20 @@ -554,7 +555,7 @@ struct lru_gen_memcg { =20 void lru_gen_init_pgdat(struct pglist_data *pgdat); void lru_gen_init_lruvec(struct lruvec *lruvec); -void lru_gen_look_around(struct page_vma_mapped_walk *pvmw); +bool lru_gen_look_around(struct page_vma_mapped_walk *pvmw); =20 void lru_gen_init_memcg(struct mem_cgroup *memcg); void lru_gen_exit_memcg(struct mem_cgroup *memcg); @@ -573,8 +574,9 @@ static inline void lru_gen_init_lruvec(struct lruvec *l= ruvec) { } =20 -static inline void lru_gen_look_around(struct page_vma_mapped_walk *pvmw) +static inline bool lru_gen_look_around(struct page_vma_mapped_walk *pvmw) { + return false; } =20 static inline void lru_gen_init_memcg(struct mem_cgroup *memcg) diff --git a/mm/rmap.c b/mm/rmap.c index 56b313aa2ebf..41e9fc25684e 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -871,13 +871,10 @@ static bool folio_referenced_one(struct folio *folio, continue; } =20 - if (pvmw.pte) { - if (lru_gen_enabled() && - pte_young(ptep_get(pvmw.pte))) { - lru_gen_look_around(&pvmw); + if (lru_gen_enabled() && pvmw.pte) { + if (lru_gen_look_around(&pvmw)) referenced++; - } - + } else if (pvmw.pte) { if (ptep_clear_flush_young_notify(vma, address, pvmw.pte)) referenced++; diff --git a/mm/vmscan.c b/mm/vmscan.c index 293120fe54f3..fd65f3466dfc 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -56,6 +56,7 @@ #include #include #include +#include =20 #include #include @@ -2596,6 +2597,11 @@ static bool should_clear_pmd_young(void) return arch_has_hw_nonleaf_pmd_young() && get_cap(LRU_GEN_NONLEAF_YOUNG); } =20 +static bool should_walk_kvm_mmu(void) +{ + return get_cap(LRU_GEN_KVM_MMU_WALK); +} + /*************************************************************************= ***** * shorthand helpers *************************************************************************= *****/ @@ -3293,7 +3299,8 @@ static bool get_next_vma(unsigned long mask, unsigned= long size, struct mm_walk return false; } =20 -static unsigned long get_pte_pfn(pte_t pte, struct vm_area_struct *vma, un= signed long addr) +static unsigned long get_pte_pfn(pte_t pte, struct vm_area_struct *vma, un= signed long addr, + struct pglist_data *pgdat) { unsigned long pfn =3D pte_pfn(pte); =20 @@ -3308,10 +3315,15 @@ static unsigned long get_pte_pfn(pte_t pte, struct = vm_area_struct *vma, unsigned if (WARN_ON_ONCE(!pfn_valid(pfn))) return -1; =20 + /* try to avoid unnecessary memory loads */ + if (pfn < pgdat->node_start_pfn || pfn >=3D pgdat_end_pfn(pgdat)) + return -1; + return pfn; } =20 -static unsigned long get_pmd_pfn(pmd_t pmd, struct vm_area_struct *vma, un= signed long addr) +static unsigned long get_pmd_pfn(pmd_t pmd, struct vm_area_struct *vma, un= signed long addr, + struct pglist_data *pgdat) { unsigned long pfn =3D pmd_pfn(pmd); =20 @@ -3326,6 +3338,10 @@ static unsigned long get_pmd_pfn(pmd_t pmd, struct v= m_area_struct *vma, unsigned if (WARN_ON_ONCE(!pfn_valid(pfn))) return -1; =20 + /* try to avoid unnecessary memory loads */ + if (pfn < pgdat->node_start_pfn || pfn >=3D pgdat_end_pfn(pgdat)) + return -1; + return pfn; } =20 @@ -3334,10 +3350,6 @@ static struct folio *get_pfn_folio(unsigned long pfn= , struct mem_cgroup *memcg, { struct folio *folio; =20 - /* try to avoid unnecessary memory loads */ - if (pfn < pgdat->node_start_pfn || pfn >=3D pgdat_end_pfn(pgdat)) - return NULL; - folio =3D pfn_folio(pfn); if (folio_nid(folio) !=3D pgdat->node_id) return NULL; @@ -3352,6 +3364,52 @@ static struct folio *get_pfn_folio(unsigned long pfn= , struct mem_cgroup *memcg, return folio; } =20 +static bool test_spte_young(struct mm_struct *mm, unsigned long addr, unsi= gned long end, + unsigned long *bitmap, unsigned long *last) +{ + if (*last > addr) + goto done; + + *last =3D end - addr > MIN_LRU_BATCH * PAGE_SIZE ? + addr + MIN_LRU_BATCH * PAGE_SIZE - 1 : end - 1; + bitmap_zero(bitmap, MIN_LRU_BATCH); + + mmu_notifier_test_young_bitmap(mm, addr, *last + 1, bitmap); +done: + return test_bit((*last - addr) / PAGE_SIZE, bitmap); +} + +static void clear_spte_young(struct mm_struct *mm, unsigned long addr, + unsigned long *bitmap, unsigned long *last) +{ + int i; + unsigned long start, end =3D *last + 1; + + if (addr + PAGE_SIZE !=3D end) + return; + + i =3D find_last_bit(bitmap, MIN_LRU_BATCH); + if (i =3D=3D MIN_LRU_BATCH) + return; + + start =3D end - (i + 1) * PAGE_SIZE; + + i =3D find_first_bit(bitmap, MIN_LRU_BATCH); + + end -=3D i * PAGE_SIZE; + + mmu_notifier_clear_young_bitmap(mm, start, end, bitmap); +} + +static void skip_spte_young(struct mm_struct *mm, unsigned long addr, + unsigned long *bitmap, unsigned long *last) +{ + if (*last > addr) + __clear_bit((*last - addr) / PAGE_SIZE, bitmap); + + clear_spte_young(mm, addr, bitmap, last); +} + static bool suitable_to_scan(int total, int young) { int n =3D clamp_t(int, cache_line_size() / sizeof(pte_t), 2, 8); @@ -3367,6 +3425,8 @@ static bool walk_pte_range(pmd_t *pmd, unsigned long = start, unsigned long end, pte_t *pte; spinlock_t *ptl; unsigned long addr; + DECLARE_BITMAP(bitmap, MIN_LRU_BATCH); + unsigned long last =3D 0; int total =3D 0; int young =3D 0; struct lru_gen_mm_walk *walk =3D args->private; @@ -3386,6 +3446,7 @@ static bool walk_pte_range(pmd_t *pmd, unsigned long = start, unsigned long end, arch_enter_lazy_mmu_mode(); restart: for (i =3D pte_index(start), addr =3D start; addr !=3D end; i++, addr += =3D PAGE_SIZE) { + bool ret; unsigned long pfn; struct folio *folio; pte_t ptent =3D ptep_get(pte + i); @@ -3393,21 +3454,28 @@ static bool walk_pte_range(pmd_t *pmd, unsigned lon= g start, unsigned long end, total++; walk->mm_stats[MM_LEAF_TOTAL]++; =20 - pfn =3D get_pte_pfn(ptent, args->vma, addr); - if (pfn =3D=3D -1) + pfn =3D get_pte_pfn(ptent, args->vma, addr, pgdat); + if (pfn =3D=3D -1) { + skip_spte_young(args->vma->vm_mm, addr, bitmap, &last); continue; + } =20 - if (!pte_young(ptent)) { + ret =3D test_spte_young(args->vma->vm_mm, addr, end, bitmap, &last); + if (!ret && !pte_young(ptent)) { + skip_spte_young(args->vma->vm_mm, addr, bitmap, &last); walk->mm_stats[MM_LEAF_OLD]++; continue; } =20 folio =3D get_pfn_folio(pfn, memcg, pgdat, walk->can_swap); - if (!folio) + if (!folio) { + skip_spte_young(args->vma->vm_mm, addr, bitmap, &last); continue; + } =20 - if (!ptep_test_and_clear_young(args->vma, addr, pte + i)) - VM_WARN_ON_ONCE(true); + clear_spte_young(args->vma->vm_mm, addr, bitmap, &last); + if (pte_young(ptent)) + ptep_test_and_clear_young(args->vma, addr, pte + i); =20 young++; walk->mm_stats[MM_LEAF_YOUNG]++; @@ -3473,22 +3541,24 @@ static void walk_pmd_range_locked(pud_t *pud, unsig= ned long addr, struct vm_area /* don't round down the first address */ addr =3D i ? (*first & PMD_MASK) + i * PMD_SIZE : *first; =20 - pfn =3D get_pmd_pfn(pmd[i], vma, addr); - if (pfn =3D=3D -1) - goto next; - - if (!pmd_trans_huge(pmd[i])) { - if (should_clear_pmd_young()) + if (pmd_present(pmd[i]) && !pmd_trans_huge(pmd[i])) { + if (should_clear_pmd_young() && !mm_has_notifiers(args->mm)) pmdp_test_and_clear_young(vma, addr, pmd + i); goto next; } =20 + pfn =3D get_pmd_pfn(pmd[i], vma, addr, pgdat); + if (pfn =3D=3D -1) + goto next; + folio =3D get_pfn_folio(pfn, memcg, pgdat, walk->can_swap); if (!folio) goto next; =20 - if (!pmdp_test_and_clear_young(vma, addr, pmd + i)) + if (!pmdp_clear_young_notify(vma, addr, pmd + i)) { + walk->mm_stats[MM_LEAF_OLD]++; goto next; + } =20 walk->mm_stats[MM_LEAF_YOUNG]++; =20 @@ -3545,19 +3615,18 @@ static void walk_pmd_range(pud_t *pud, unsigned lon= g start, unsigned long end, } =20 if (pmd_trans_huge(val)) { - unsigned long pfn =3D pmd_pfn(val); struct pglist_data *pgdat =3D lruvec_pgdat(walk->lruvec); + unsigned long pfn =3D get_pmd_pfn(val, vma, addr, pgdat); =20 walk->mm_stats[MM_LEAF_TOTAL]++; =20 - if (!pmd_young(val)) { - walk->mm_stats[MM_LEAF_OLD]++; + if (pfn =3D=3D -1) continue; - } =20 - /* try to avoid unnecessary memory loads */ - if (pfn < pgdat->node_start_pfn || pfn >=3D pgdat_end_pfn(pgdat)) + if (!pmd_young(val) && !mm_has_notifiers(args->mm)) { + walk->mm_stats[MM_LEAF_OLD]++; continue; + } =20 walk_pmd_range_locked(pud, addr, vma, args, bitmap, &first); continue; @@ -3565,7 +3634,7 @@ static void walk_pmd_range(pud_t *pud, unsigned long = start, unsigned long end, =20 walk->mm_stats[MM_NONLEAF_TOTAL]++; =20 - if (should_clear_pmd_young()) { + if (should_clear_pmd_young() && !mm_has_notifiers(args->mm)) { if (!pmd_young(val)) continue; =20 @@ -3646,6 +3715,9 @@ static void walk_mm(struct mm_struct *mm, struct lru_= gen_mm_walk *walk) struct lruvec *lruvec =3D walk->lruvec; struct mem_cgroup *memcg =3D lruvec_memcg(lruvec); =20 + if (!should_walk_kvm_mmu() && mm_has_notifiers(mm)) + return; + walk->next_addr =3D FIRST_USER_ADDRESS; =20 do { @@ -4011,6 +4083,23 @@ static void lru_gen_age_node(struct pglist_data *pgd= at, struct scan_control *sc) * rmap/PT walk feedback *************************************************************************= *****/ =20 +static bool should_look_around(struct vm_area_struct *vma, unsigned long a= ddr, + pte_t *pte, int *young) +{ + int ret =3D mmu_notifier_clear_young(vma->vm_mm, addr, addr + PAGE_SIZE); + + if (pte_young(ptep_get(pte))) { + ptep_test_and_clear_young(vma, addr, pte); + *young =3D true; + return true; + } + + if (ret) + *young =3D true; + + return ret & MMU_NOTIFIER_YOUNG_FAST; +} + /* * This function exploits spatial locality when shrink_folio_list() walks = the * rmap. It scans the adjacent PTEs of a young PTE and promotes hot pages.= If @@ -4018,12 +4107,14 @@ static void lru_gen_age_node(struct pglist_data *pg= dat, struct scan_control *sc) * the PTE table to the Bloom filter. This forms a feedback loop between t= he * eviction and the aging. */ -void lru_gen_look_around(struct page_vma_mapped_walk *pvmw) +bool lru_gen_look_around(struct page_vma_mapped_walk *pvmw) { int i; unsigned long start; unsigned long end; struct lru_gen_mm_walk *walk; + DECLARE_BITMAP(bitmap, MIN_LRU_BATCH); + unsigned long last =3D 0; int young =3D 0; pte_t *pte =3D pvmw->pte; unsigned long addr =3D pvmw->address; @@ -4040,12 +4131,15 @@ void lru_gen_look_around(struct page_vma_mapped_wal= k *pvmw) lockdep_assert_held(pvmw->ptl); VM_WARN_ON_ONCE_FOLIO(folio_test_lru(folio), folio); =20 + if (!should_look_around(pvmw->vma, addr, pte, &young)) + return young; + if (spin_is_contended(pvmw->ptl)) - return; + return young; =20 /* exclude special VMAs containing anon pages from COW */ if (vma->vm_flags & VM_SPECIAL) - return; + return young; =20 /* avoid taking the LRU lock under the PTL when possible */ walk =3D current->reclaim_state ? current->reclaim_state->mm_walk : NULL; @@ -4053,6 +4147,9 @@ void lru_gen_look_around(struct page_vma_mapped_walk = *pvmw) start =3D max(addr & PMD_MASK, vma->vm_start); end =3D min(addr | ~PMD_MASK, vma->vm_end - 1) + 1; =20 + if (end - start =3D=3D PAGE_SIZE) + return young; + if (end - start > MIN_LRU_BATCH * PAGE_SIZE) { if (addr - start < MIN_LRU_BATCH * PAGE_SIZE / 2) end =3D start + MIN_LRU_BATCH * PAGE_SIZE; @@ -4066,29 +4163,38 @@ void lru_gen_look_around(struct page_vma_mapped_wal= k *pvmw) =20 /* folio_update_gen() requires stable folio_memcg() */ if (!mem_cgroup_trylock_pages(memcg)) - return; + return young; =20 arch_enter_lazy_mmu_mode(); =20 pte -=3D (addr - start) / PAGE_SIZE; =20 for (i =3D 0, addr =3D start; addr !=3D end; i++, addr +=3D PAGE_SIZE) { + bool ret; unsigned long pfn; pte_t ptent =3D ptep_get(pte + i); =20 - pfn =3D get_pte_pfn(ptent, vma, addr); - if (pfn =3D=3D -1) + pfn =3D get_pte_pfn(ptent, vma, addr, pgdat); + if (pfn =3D=3D -1) { + skip_spte_young(vma->vm_mm, addr, bitmap, &last); continue; + } =20 - if (!pte_young(ptent)) + ret =3D test_spte_young(pvmw->vma->vm_mm, addr, end, bitmap, &last); + if (!ret && !pte_young(ptent)) { + skip_spte_young(pvmw->vma->vm_mm, addr, bitmap, &last); continue; + } =20 folio =3D get_pfn_folio(pfn, memcg, pgdat, can_swap); - if (!folio) + if (!folio) { + skip_spte_young(vma->vm_mm, addr, bitmap, &last); continue; + } =20 - if (!ptep_test_and_clear_young(vma, addr, pte + i)) - VM_WARN_ON_ONCE(true); + clear_spte_young(vma->vm_mm, addr, bitmap, &last); + if (pte_young(ptent)) + ptep_test_and_clear_young(vma, addr, pte + i); =20 young++; =20 @@ -4118,6 +4224,8 @@ void lru_gen_look_around(struct page_vma_mapped_walk = *pvmw) /* feedback from rmap walkers to page table walkers */ if (mm_state && suitable_to_scan(i, young)) update_bloom_filter(mm_state, max_seq, pvmw->pmd); + + return young; } =20 /*************************************************************************= ***** @@ -5154,6 +5262,9 @@ static ssize_t enabled_show(struct kobject *kobj, str= uct kobj_attribute *attr, c if (should_clear_pmd_young()) caps |=3D BIT(LRU_GEN_NONLEAF_YOUNG); =20 + if (should_walk_kvm_mmu()) + caps |=3D BIT(LRU_GEN_KVM_MMU_WALK); + return sysfs_emit(buf, "0x%04x\n", caps); } =20 --=20 2.44.0.478.gd926399ef9-goog