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Message-ID: <20241019012940.3656292-3-jthoughton@google.com>
Date: Sat, 19 Oct 2024 01:29:39 +0000
From: James Houghton <jthoughton@...gle.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini <pbonzini@...hat.com>,
David Matlack <dmatlack@...gle.com>, David Rientjes <rientjes@...gle.com>,
James Houghton <jthoughton@...gle.com>, Oliver Upton <oliver.upton@...ux.dev>,
David Stevens <stevensd@...gle.com>, Yu Zhao <yuzhao@...gle.com>, Wei Xu <weixugc@...gle.com>,
Axel Rasmussen <axelrasmussen@...gle.com>, kvm@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: [PATCH 2/2] mm: multi-gen LRU: use {ptep,pmdp}_clear_young_notify()
From: Yu Zhao <yuzhao@...gle.com>
When the MM_WALK capability is enabled, memory that is mostly accessed
by a VM appears younger than it really is, therefore this memory will be
less likely to be evicted. Therefore, the presence of a running VM can
significantly increase swap-outs for non-VM memory, regressing the
performance for the rest of the system.
Fix this regression by always calling {ptep,pmdp}_clear_young_notify()
whenever we clear the young bits on PMDs/PTEs.
Fixes: bd74fdaea146 ("mm: multi-gen LRU: support page table walks")
Reported-by: David Stevens <stevensd@...gle.com>
Signed-off-by: Yu Zhao <yuzhao@...gle.com>
Signed-off-by: James Houghton <jthoughton@...gle.com>
---
include/linux/mmzone.h | 5 ++-
mm/rmap.c | 9 ++---
mm/vmscan.c | 91 +++++++++++++++++++++++-------------------
3 files changed, 55 insertions(+), 50 deletions(-)
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 691c635d8d1f..2e8c4307c728 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -557,7 +557,7 @@ struct lru_gen_memcg {
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);
void lru_gen_init_memcg(struct mem_cgroup *memcg);
void lru_gen_exit_memcg(struct mem_cgroup *memcg);
@@ -576,8 +576,9 @@ static inline void lru_gen_init_lruvec(struct lruvec *lruvec)
{
}
-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;
}
static inline void lru_gen_init_memcg(struct mem_cgroup *memcg)
diff --git a/mm/rmap.c b/mm/rmap.c
index 2c561b1e52cc..4785a693857a 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -896,13 +896,10 @@ static bool folio_referenced_one(struct folio *folio,
return false;
}
- 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 60669f8bba46..29c098790b01 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -56,6 +56,7 @@
#include <linux/khugepaged.h>
#include <linux/rculist_nulls.h>
#include <linux/random.h>
+#include <linux/mmu_notifier.h>
#include <asm/tlbflush.h>
#include <asm/div64.h>
@@ -3293,7 +3294,8 @@ static bool get_next_vma(unsigned long mask, unsigned long size, struct mm_walk
return false;
}
-static unsigned long get_pte_pfn(pte_t pte, struct vm_area_struct *vma, unsigned long addr)
+static unsigned long get_pte_pfn(pte_t pte, struct vm_area_struct *vma, unsigned long addr,
+ struct pglist_data *pgdat)
{
unsigned long pfn = pte_pfn(pte);
@@ -3305,13 +3307,20 @@ static unsigned long get_pte_pfn(pte_t pte, struct vm_area_struct *vma, unsigned
if (WARN_ON_ONCE(pte_devmap(pte) || pte_special(pte)))
return -1;
+ if (!pte_young(pte) && !mm_has_notifiers(vma->vm_mm))
+ return -1;
+
if (WARN_ON_ONCE(!pfn_valid(pfn)))
return -1;
+ if (pfn < pgdat->node_start_pfn || pfn >= pgdat_end_pfn(pgdat))
+ return -1;
+
return pfn;
}
-static unsigned long get_pmd_pfn(pmd_t pmd, struct vm_area_struct *vma, unsigned long addr)
+static unsigned long get_pmd_pfn(pmd_t pmd, struct vm_area_struct *vma, unsigned long addr,
+ struct pglist_data *pgdat)
{
unsigned long pfn = pmd_pfn(pmd);
@@ -3323,9 +3332,15 @@ static unsigned long get_pmd_pfn(pmd_t pmd, struct vm_area_struct *vma, unsigned
if (WARN_ON_ONCE(pmd_devmap(pmd)))
return -1;
+ if (!pmd_young(pmd) && !mm_has_notifiers(vma->vm_mm))
+ return -1;
+
if (WARN_ON_ONCE(!pfn_valid(pfn)))
return -1;
+ if (pfn < pgdat->node_start_pfn || pfn >= pgdat_end_pfn(pgdat))
+ return -1;
+
return pfn;
}
@@ -3334,10 +3349,6 @@ static struct folio *get_pfn_folio(unsigned long pfn, struct mem_cgroup *memcg,
{
struct folio *folio;
- /* try to avoid unnecessary memory loads */
- if (pfn < pgdat->node_start_pfn || pfn >= pgdat_end_pfn(pgdat))
- return NULL;
-
folio = pfn_folio(pfn);
if (folio_nid(folio) != pgdat->node_id)
return NULL;
@@ -3400,20 +3411,16 @@ static bool walk_pte_range(pmd_t *pmd, unsigned long start, unsigned long end,
total++;
walk->mm_stats[MM_LEAF_TOTAL]++;
- pfn = get_pte_pfn(ptent, args->vma, addr);
+ pfn = get_pte_pfn(ptent, args->vma, addr, pgdat);
if (pfn == -1)
continue;
- if (!pte_young(ptent)) {
- continue;
- }
-
folio = get_pfn_folio(pfn, memcg, pgdat, walk->can_swap);
if (!folio)
continue;
- if (!ptep_test_and_clear_young(args->vma, addr, pte + i))
- VM_WARN_ON_ONCE(true);
+ if (!ptep_clear_young_notify(args->vma, addr, pte + i))
+ continue;
young++;
walk->mm_stats[MM_LEAF_YOUNG]++;
@@ -3479,21 +3486,22 @@ static void walk_pmd_range_locked(pud_t *pud, unsigned long addr, struct vm_area
/* don't round down the first address */
addr = i ? (*first & PMD_MASK) + i * PMD_SIZE : *first;
- pfn = get_pmd_pfn(pmd[i], vma, addr);
- if (pfn == -1)
- goto next;
-
- if (!pmd_trans_huge(pmd[i])) {
- if (!walk->force_scan && should_clear_pmd_young())
+ if (pmd_present(pmd[i]) && !pmd_trans_huge(pmd[i])) {
+ if (!walk->force_scan && should_clear_pmd_young() &&
+ !mm_has_notifiers(args->mm))
pmdp_test_and_clear_young(vma, addr, pmd + i);
goto next;
}
+ pfn = get_pmd_pfn(pmd[i], vma, addr, pgdat);
+ if (pfn == -1)
+ goto next;
+
folio = get_pfn_folio(pfn, memcg, pgdat, walk->can_swap);
if (!folio)
goto next;
- if (!pmdp_test_and_clear_young(vma, addr, pmd + i))
+ if (!pmdp_clear_young_notify(vma, addr, pmd + i))
goto next;
walk->mm_stats[MM_LEAF_YOUNG]++;
@@ -3551,24 +3559,18 @@ static void walk_pmd_range(pud_t *pud, unsigned long start, unsigned long end,
}
if (pmd_trans_huge(val)) {
- unsigned long pfn = pmd_pfn(val);
struct pglist_data *pgdat = lruvec_pgdat(walk->lruvec);
+ unsigned long pfn = get_pmd_pfn(val, vma, addr, pgdat);
walk->mm_stats[MM_LEAF_TOTAL]++;
- if (!pmd_young(val)) {
- continue;
- }
-
- /* try to avoid unnecessary memory loads */
- if (pfn < pgdat->node_start_pfn || pfn >= pgdat_end_pfn(pgdat))
- continue;
-
- walk_pmd_range_locked(pud, addr, vma, args, bitmap, &first);
+ if (pfn != -1)
+ walk_pmd_range_locked(pud, addr, vma, args, bitmap, &first);
continue;
}
- if (!walk->force_scan && should_clear_pmd_young()) {
+ if (!walk->force_scan && should_clear_pmd_young() &&
+ !mm_has_notifiers(args->mm)) {
if (!pmd_young(val))
continue;
@@ -4042,13 +4044,13 @@ static void lru_gen_age_node(struct pglist_data *pgdat, struct scan_control *sc)
* the PTE table to the Bloom filter. This forms a feedback loop between the
* 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;
- int young = 0;
+ int young = 1;
pte_t *pte = pvmw->pte;
unsigned long addr = pvmw->address;
struct vm_area_struct *vma = pvmw->vma;
@@ -4064,12 +4066,15 @@ void lru_gen_look_around(struct page_vma_mapped_walk *pvmw)
lockdep_assert_held(pvmw->ptl);
VM_WARN_ON_ONCE_FOLIO(folio_test_lru(folio), folio);
+ if (!ptep_clear_young_notify(vma, addr, pte))
+ return false;
+
if (spin_is_contended(pvmw->ptl))
- return;
+ return true;
/* exclude special VMAs containing anon pages from COW */
if (vma->vm_flags & VM_SPECIAL)
- return;
+ return true;
/* avoid taking the LRU lock under the PTL when possible */
walk = current->reclaim_state ? current->reclaim_state->mm_walk : NULL;
@@ -4077,6 +4082,9 @@ void lru_gen_look_around(struct page_vma_mapped_walk *pvmw)
start = max(addr & PMD_MASK, vma->vm_start);
end = min(addr | ~PMD_MASK, vma->vm_end - 1) + 1;
+ if (end - start == PAGE_SIZE)
+ return true;
+
if (end - start > MIN_LRU_BATCH * PAGE_SIZE) {
if (addr - start < MIN_LRU_BATCH * PAGE_SIZE / 2)
end = start + MIN_LRU_BATCH * PAGE_SIZE;
@@ -4090,7 +4098,7 @@ void lru_gen_look_around(struct page_vma_mapped_walk *pvmw)
/* folio_update_gen() requires stable folio_memcg() */
if (!mem_cgroup_trylock_pages(memcg))
- return;
+ return true;
arch_enter_lazy_mmu_mode();
@@ -4100,19 +4108,16 @@ void lru_gen_look_around(struct page_vma_mapped_walk *pvmw)
unsigned long pfn;
pte_t ptent = ptep_get(pte + i);
- pfn = get_pte_pfn(ptent, vma, addr);
+ pfn = get_pte_pfn(ptent, vma, addr, pgdat);
if (pfn == -1)
continue;
- if (!pte_young(ptent))
- continue;
-
folio = get_pfn_folio(pfn, memcg, pgdat, can_swap);
if (!folio)
continue;
- if (!ptep_test_and_clear_young(vma, addr, pte + i))
- VM_WARN_ON_ONCE(true);
+ if (!ptep_clear_young_notify(vma, addr, pte + i))
+ continue;
young++;
@@ -4144,6 +4149,8 @@ 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 true;
}
/******************************************************************************
--
2.47.0.105.g07ac214952-goog
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