[PATCH v1 1/4] mm: introduce MADV_COLD

From: Minchan Kim
Date: Mon Jun 03 2019 - 01:41:01 EST

When a process expects no accesses to a certain memory range, it could
give a hint to kernel that the pages can be reclaimed when memory pressure
happens but data should be preserved for future use. This could reduce
workingset eviction so it ends up increasing performance.

This patch introduces the new MADV_COLD hint to madvise(2) syscall.
MADV_COLD can be used by a process to mark a memory range as not expected
to be used in the near future. The hint can help kernel in deciding which
pages to evict early during memory pressure.

It works for every LRU pages like MADV_[DONTNEED|FREE]. IOW, It moves

active file page -> inactive file LRU
active anon page -> inacdtive anon LRU

Unlike MADV_FREE, it doesn't move active anonymous pages to inactive
files's head because MADV_COLD is a little bit different symantic.
MADV_FREE means it's okay to discard when the memory pressure because
the content of the page is *garbage* so freeing such pages is almost zero
overhead since we don't need to swap out and access afterward causes just
minor fault. Thus, it would make sense to put those freeable pages in
inactive file LRU to compete other used-once pages. Even, it could
give a bonus to make them be reclaimed on swapless system. However,
MADV_COLD doesn't mean garbage so reclaiming them requires swap-out/in
in the end. So it's better to move inactive anon's LRU list, not file LRU.
Furthermore, it would help to avoid unnecessary scanning of cold anonymous
if system doesn't have a swap device.

All of error rule is same with MADV_DONTNEED.

Note:
This hint works with only private pages(IOW, page_mapcount(page) < 2)
because shared page could have more chance to be accessed from other
processes sharing the page although the caller reset the reference bits.
It ends up preventing the reclaim of the page and wastes CPU cycle.

* RFCv2
* add more description - mhocko

* RFCv1
* renaming from MADV_COOL to MADV_COLD - hannes

* internal review
* use clear_page_youn in deactivate_page - joelaf
* Revise the description - surenb
* Renaming from MADV_WARM to MADV_COOL - surenb

Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
---
include/linux/page-flags.h | 1 +
include/linux/page_idle.h | 15 ++++
include/linux/swap.h | 1 +
include/uapi/asm-generic/mman-common.h | 1 +
mm/internal.h | 2 +-
mm/madvise.c | 115 ++++++++++++++++++++++++-
mm/oom_kill.c | 2 +-
mm/swap.c | 43 +++++++++
8 files changed, 176 insertions(+), 4 deletions(-)

diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 9f8712a4b1a5..58b06654c8dd 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -424,6 +424,7 @@ static inline bool set_hwpoison_free_buddy_page(struct page *page)
TESTPAGEFLAG(Young, young, PF_ANY)
SETPAGEFLAG(Young, young, PF_ANY)
TESTCLEARFLAG(Young, young, PF_ANY)
+CLEARPAGEFLAG(Young, young, PF_ANY)
PAGEFLAG(Idle, idle, PF_ANY)
#endif

diff --git a/include/linux/page_idle.h b/include/linux/page_idle.h
index 1e894d34bdce..f3f43b317150 100644
--- a/include/linux/page_idle.h
+++ b/include/linux/page_idle.h
@@ -19,6 +19,11 @@ static inline void set_page_young(struct page *page)
SetPageYoung(page);
}

+static inline void clear_page_young(struct page *page)
+{
+ ClearPageYoung(page);
+}
+
static inline bool test_and_clear_page_young(struct page *page)
{
return TestClearPageYoung(page);
@@ -65,6 +70,16 @@ static inline void set_page_young(struct page *page)
set_bit(PAGE_EXT_YOUNG, &page_ext->flags);
}

+static void clear_page_young(struct page *page)
+{
+ struct page_ext *page_ext = lookup_page_ext(page);
+
+ if (unlikely(!page_ext))
+ return;
+
+ clear_bit(PAGE_EXT_YOUNG, &page_ext->flags);
+}
+
static inline bool test_and_clear_page_young(struct page *page)
{
struct page_ext *page_ext = lookup_page_ext(page);
diff --git a/include/linux/swap.h b/include/linux/swap.h
index de2c67a33b7e..0ce997edb8bb 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -340,6 +340,7 @@ extern void lru_add_drain_cpu(int cpu);
extern void lru_add_drain_all(void);
extern void rotate_reclaimable_page(struct page *page);
extern void deactivate_file_page(struct page *page);
+extern void deactivate_page(struct page *page);
extern void mark_page_lazyfree(struct page *page);
extern void swap_setup(void);

diff --git a/include/uapi/asm-generic/mman-common.h b/include/uapi/asm-generic/mman-common.h
index bea0278f65ab..1190f4e7f7b9 100644
--- a/include/uapi/asm-generic/mman-common.h
+++ b/include/uapi/asm-generic/mman-common.h
@@ -43,6 +43,7 @@
#define MADV_SEQUENTIAL 2 /* expect sequential page references */
#define MADV_WILLNEED 3 /* will need these pages */
#define MADV_DONTNEED 4 /* don't need these pages */
+#define MADV_COLD 5 /* deactivatie these pages */

/* common parameters: try to keep these consistent across architectures */
#define MADV_FREE 8 /* free pages only if memory pressure */
diff --git a/mm/internal.h b/mm/internal.h
index 9eeaf2b95166..75a4f96ec0fb 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -43,7 +43,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf);
void free_pgtables(struct mmu_gather *tlb, struct vm_area_struct *start_vma,
unsigned long floor, unsigned long ceiling);

-static inline bool can_madv_dontneed_vma(struct vm_area_struct *vma)
+static inline bool can_madv_lru_vma(struct vm_area_struct *vma)
{
return !(vma->vm_flags & (VM_LOCKED|VM_HUGETLB|VM_PFNMAP));
}
diff --git a/mm/madvise.c b/mm/madvise.c
index 628022e674a7..ab158766858a 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -40,6 +40,7 @@ static int madvise_need_mmap_write(int behavior)
case MADV_REMOVE:
case MADV_WILLNEED:
case MADV_DONTNEED:
+ case MADV_COLD:
case MADV_FREE:
return 0;
default:
@@ -307,6 +308,113 @@ static long madvise_willneed(struct vm_area_struct *vma,
return 0;
}

+static int madvise_cold_pte_range(pmd_t *pmd, unsigned long addr,
+ unsigned long end, struct mm_walk *walk)
+{
+ pte_t *orig_pte, *pte, ptent;
+ spinlock_t *ptl;
+ struct page *page;
+ struct vm_area_struct *vma = walk->vma;
+ unsigned long next;
+
+ next = pmd_addr_end(addr, end);
+ if (pmd_trans_huge(*pmd)) {
+ ptl = pmd_trans_huge_lock(pmd, vma);
+ if (!ptl)
+ return 0;
+
+ if (is_huge_zero_pmd(*pmd))
+ goto huge_unlock;
+
+ page = pmd_page(*pmd);
+ if (page_mapcount(page) > 1)
+ goto huge_unlock;
+
+ if (next - addr != HPAGE_PMD_SIZE) {
+ int err;
+
+ get_page(page);
+ spin_unlock(ptl);
+ lock_page(page);
+ err = split_huge_page(page);
+ unlock_page(page);
+ put_page(page);
+ if (!err)
+ goto regular_page;
+ return 0;
+ }
+
+ pmdp_test_and_clear_young(vma, addr, pmd);
+ deactivate_page(page);
+huge_unlock:
+ spin_unlock(ptl);
+ return 0;
+ }
+
+ if (pmd_trans_unstable(pmd))
+ return 0;
+
+regular_page:
+ orig_pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
+ for (pte = orig_pte; addr < end; pte++, addr += PAGE_SIZE) {
+ ptent = *pte;
+
+ if (pte_none(ptent))
+ continue;
+
+ if (!pte_present(ptent))
+ continue;
+
+ page = vm_normal_page(vma, addr, ptent);
+ if (!page)
+ continue;
+
+ if (page_mapcount(page) > 1)
+ continue;
+
+ ptep_test_and_clear_young(vma, addr, pte);
+ deactivate_page(page);
+ }
+
+ pte_unmap_unlock(orig_pte, ptl);
+ cond_resched();
+
+ return 0;
+}
+
+static void madvise_cold_page_range(struct mmu_gather *tlb,
+ struct vm_area_struct *vma,
+ unsigned long addr, unsigned long end)
+{
+ struct mm_walk cool_walk = {
+ .pmd_entry = madvise_cold_pte_range,
+ .mm = vma->vm_mm,
+ };
+
+ tlb_start_vma(tlb, vma);
+ walk_page_range(addr, end, &cool_walk);
+ tlb_end_vma(tlb, vma);
+}
+
+static long madvise_cold(struct vm_area_struct *vma,
+ struct vm_area_struct **prev,
+ unsigned long start_addr, unsigned long end_addr)
+{
+ struct mm_struct *mm = vma->vm_mm;
+ struct mmu_gather tlb;
+
+ *prev = vma;
+ if (!can_madv_lru_vma(vma))
+ return -EINVAL;
+
+ lru_add_drain();
+ tlb_gather_mmu(&tlb, mm, start_addr, end_addr);
+ madvise_cold_page_range(&tlb, vma, start_addr, end_addr);
+ tlb_finish_mmu(&tlb, start_addr, end_addr);
+
+ return 0;
+}
+
static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr,
unsigned long end, struct mm_walk *walk)

@@ -519,7 +627,7 @@ static long madvise_dontneed_free(struct vm_area_struct *vma,
int behavior)
{
*prev = vma;
- if (!can_madv_dontneed_vma(vma))
+ if (!can_madv_lru_vma(vma))
return -EINVAL;

if (!userfaultfd_remove(vma, start, end)) {
@@ -541,7 +649,7 @@ static long madvise_dontneed_free(struct vm_area_struct *vma,
*/
return -ENOMEM;
}
- if (!can_madv_dontneed_vma(vma))
+ if (!can_madv_lru_vma(vma))
return -EINVAL;
if (end > vma->vm_end) {
/*
@@ -695,6 +803,8 @@ madvise_vma(struct vm_area_struct *vma, struct vm_area_struct **prev,
return madvise_remove(vma, prev, start, end);
case MADV_WILLNEED:
return madvise_willneed(vma, prev, start, end);
+ case MADV_COLD:
+ return madvise_cold(vma, prev, start, end);
case MADV_FREE:
case MADV_DONTNEED:
return madvise_dontneed_free(vma, prev, start, end, behavior);
@@ -716,6 +826,7 @@ madvise_behavior_valid(int behavior)
case MADV_WILLNEED:
case MADV_DONTNEED:
case MADV_FREE:
+ case MADV_COLD:
#ifdef CONFIG_KSM
case MADV_MERGEABLE:
case MADV_UNMERGEABLE:
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 5a58778c91d4..f73d5f5145f0 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -515,7 +515,7 @@ bool __oom_reap_task_mm(struct mm_struct *mm)
set_bit(MMF_UNSTABLE, &mm->flags);

for (vma = mm->mmap ; vma; vma = vma->vm_next) {
- if (!can_madv_dontneed_vma(vma))
+ if (!can_madv_lru_vma(vma))
continue;

/*
diff --git a/mm/swap.c b/mm/swap.c
index 7b079976cbec..cebedab15aa2 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -47,6 +47,7 @@ int page_cluster;
static DEFINE_PER_CPU(struct pagevec, lru_add_pvec);
static DEFINE_PER_CPU(struct pagevec, lru_rotate_pvecs);
static DEFINE_PER_CPU(struct pagevec, lru_deactivate_file_pvecs);
+static DEFINE_PER_CPU(struct pagevec, lru_deactivate_pvecs);
static DEFINE_PER_CPU(struct pagevec, lru_lazyfree_pvecs);
#ifdef CONFIG_SMP
static DEFINE_PER_CPU(struct pagevec, activate_page_pvecs);
@@ -538,6 +539,23 @@ static void lru_deactivate_file_fn(struct page *page, struct lruvec *lruvec,
update_page_reclaim_stat(lruvec, file, 0);
}

+static void lru_deactivate_fn(struct page *page, struct lruvec *lruvec,
+ void *arg)
+{
+ if (PageLRU(page) && PageActive(page) && !PageUnevictable(page)) {
+ int file = page_is_file_cache(page);
+ int lru = page_lru_base_type(page);
+
+ del_page_from_lru_list(page, lruvec, lru + LRU_ACTIVE);
+ ClearPageActive(page);
+ ClearPageReferenced(page);
+ clear_page_young(page);
+ add_page_to_lru_list(page, lruvec, lru);
+
+ __count_vm_events(PGDEACTIVATE, hpage_nr_pages(page));
+ update_page_reclaim_stat(lruvec, file, 0);
+ }
+}

static void lru_lazyfree_fn(struct page *page, struct lruvec *lruvec,
void *arg)
@@ -590,6 +608,10 @@ void lru_add_drain_cpu(int cpu)
if (pagevec_count(pvec))
pagevec_lru_move_fn(pvec, lru_deactivate_file_fn, NULL);

+ pvec = &per_cpu(lru_deactivate_pvecs, cpu);
+ if (pagevec_count(pvec))
+ pagevec_lru_move_fn(pvec, lru_deactivate_fn, NULL);
+
pvec = &per_cpu(lru_lazyfree_pvecs, cpu);
if (pagevec_count(pvec))
pagevec_lru_move_fn(pvec, lru_lazyfree_fn, NULL);
@@ -623,6 +645,26 @@ void deactivate_file_page(struct page *page)
}
}

+/*
+ * deactivate_page - deactivate a page
+ * @page: page to deactivate
+ *
+ * deactivate_page() moves @page to the inactive list if @page was on the active
+ * list and was not an unevictable page. This is done to accelerate the reclaim
+ * of @page.
+ */
+void deactivate_page(struct page *page)
+{
+ if (PageLRU(page) && PageActive(page) && !PageUnevictable(page)) {
+ struct pagevec *pvec = &get_cpu_var(lru_deactivate_pvecs);
+
+ get_page(page);
+ if (!pagevec_add(pvec, page) || PageCompound(page))
+ pagevec_lru_move_fn(pvec, lru_deactivate_fn, NULL);
+ put_cpu_var(lru_deactivate_pvecs);
+ }
+}
+
/**
* mark_page_lazyfree - make an anon page lazyfree
* @page: page to deactivate
@@ -687,6 +729,7 @@ void lru_add_drain_all(void)
if (pagevec_count(&per_cpu(lru_add_pvec, cpu)) ||
pagevec_count(&per_cpu(lru_rotate_pvecs, cpu)) ||
pagevec_count(&per_cpu(lru_deactivate_file_pvecs, cpu)) ||
+ pagevec_count(&per_cpu(lru_deactivate_pvecs, cpu)) ||
pagevec_count(&per_cpu(lru_lazyfree_pvecs, cpu)) ||
need_activate_page_drain(cpu)) {
INIT_WORK(work, lru_add_drain_per_cpu);
--
2.22.0.rc1.311.g5d7573a151-goog