Hi Minchan,
Couple comments inline.
Thanks!
On Sun, Jul 14, 2019 at 4:34 PM Minchan Kim <minchan@xxxxxxxxxx> wrote:
>
> 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
> file LRU'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. It makes sense for
> implmentaion point of view, too because it's not swapbacked memory any
> longer until it would be re-dirtied. 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 bigger
> cost. Since we have designed VM LRU aging based on cost-model, anonymous
> cold pages would be better to position inactive anon's LRU list, not file
> LRU. Furthermore, it would help to avoid unnecessary scanning if system
> doesn't have a swap device. Let's start simpler way without adding
> complexity at this moment. However, keep in mind, too that it's a caveat
> that workloads with a lot of pages cache are likely to ignore MADV_COLD
> on anonymous memory because we rarely age anonymous LRU lists.
>
> * man-page material
>
> MADV_COLD (since Linux x.x)
>
> Pages in the specified regions will be treated as less-recently-accessed
> compared to pages in the system with similar access frequencies.
> In contrast to MADV_FREE, the contents of the region are preserved
> regardless of subsequent writes to pages.
>
> MADV_COLD cannot be applied to locked pages, Huge TLB pages, or VM_PFNMAP
> pages.
>
> * v2
> * add up the warn with lots of page cache workload - mhocko
> * add man page stuff - dave
>
> * v1
> * remove page_mapcount filter - hannes, mhocko
> * remove idle page handling - joelaf
>
> * 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
>
> Acked-by: Michal Hocko <mhocko@xxxxxxxx>
> Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>
> Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
> ---
> include/linux/swap.h | 1 +
> include/uapi/asm-generic/mman-common.h | 1 +
> mm/internal.h | 2 +-
> mm/madvise.c | 180 ++++++++++++++++++++++++-
> mm/oom_kill.c | 2 +-
> mm/swap.c | 42 ++++++
> 6 files changed, 224 insertions(+), 4 deletions(-)
>
> 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 63b1f506ea67..ef8a56927b12 100644
> --- a/include/uapi/asm-generic/mman-common.h
> +++ b/include/uapi/asm-generic/mman-common.h
> @@ -45,6 +45,7 @@
> #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 */
s/deactivatie/deactivate
>
> /* 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 f53a14d67538..c61b215ff265 100644
> --- a/mm/internal.h
> +++ b/mm/internal.h
> @@ -39,7 +39,7 @@ 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 968df3aa069f..bae0055f9724 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 +308,178 @@ 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)
> +{
> + struct mmu_gather *tlb = walk->private;
> + struct mm_struct *mm = tlb->mm;
> + struct vm_area_struct *vma = walk->vma;
> + pte_t *orig_pte, *pte, ptent;
> + spinlock_t *ptl;
> + struct page *page;
> + unsigned long next;
> +
> + next = pmd_addr_end(addr, end);
> + if (pmd_trans_huge(*pmd)) {
> + pmd_t orig_pmd;
> +
> + tlb_change_page_size(tlb, HPAGE_PMD_SIZE);
> + ptl = pmd_trans_huge_lock(pmd, vma);
> + if (!ptl)
> + return 0;
> +
> + orig_pmd = *pmd;
> + if (is_huge_zero_pmd(orig_pmd))
> + goto huge_unlock;
> +
> + if (unlikely(!pmd_present(orig_pmd))) {
> + VM_BUG_ON(thp_migration_supported() &&
> + !is_pmd_migration_entry(orig_pmd));
> + goto huge_unlock;
> + }
> +
> + page = pmd_page(orig_pmd);
> + if (next - addr != HPAGE_PMD_SIZE) {
> + int err;
> +
> + if (page_mapcount(page) != 1)
> + goto huge_unlock;
> +
> + 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;
> + }
> +
> + if (pmd_young(orig_pmd)) {
> + pmdp_invalidate(vma, addr, pmd);
> + orig_pmd = pmd_mkold(orig_pmd);
> +
> + set_pmd_at(mm, addr, pmd, orig_pmd);
> + tlb_remove_pmd_tlb_entry(tlb, pmd, addr);
> + }
> +
> + test_and_clear_page_young(page);
> + deactivate_page(page);
> +huge_unlock:
> + spin_unlock(ptl);
> + return 0;
> + }
> +
> + if (pmd_trans_unstable(pmd))
> + return 0;
> +
> +regular_page:
> + tlb_change_page_size(tlb, PAGE_SIZE);
> + orig_pte = pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
> + flush_tlb_batched_pending(mm);
> + arch_enter_lazy_mmu_mode();
> + for (; 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;
> +
> + /*
> + * Creating a THP page is expensive so split it only if we
> + * are sure it's worth. Split it if we are only owner.
> + */
> + if (PageTransCompound(page)) {
> + if (page_mapcount(page) != 1)
> + break;
> + get_page(page);
> + if (!trylock_page(page)) {
> + put_page(page);
> + break;
> + }
> + pte_unmap_unlock(orig_pte, ptl);
> + if (split_huge_page(page)) {
> + unlock_page(page);
> + put_page(page);
> + pte_offset_map_lock(mm, pmd, addr, &ptl);
> + break;
> + }
> + unlock_page(page);
> + put_page(page);
> + pte = pte_offset_map_lock(mm, pmd, addr, &ptl);
> + pte--;
> + addr -= PAGE_SIZE;
> + continue;
> + }
> +
> + VM_BUG_ON_PAGE(PageTransCompound(page), page);
> +
> + if (pte_young(ptent)) {
> + ptent = ptep_get_and_clear_full(mm, addr, pte,
> + tlb->fullmm);
> + ptent = pte_mkold(ptent);
> + set_pte_at(mm, addr, pte, ptent);
> + tlb_remove_tlb_entry(tlb, pte, addr);
> + }
> +
> + /*
> + * We are deactivating a page for accelerating reclaiming.
> + * VM couldn't reclaim the page unless we clear PG_young.
> + * As a side effect, it makes confuse idle-page tracking
> + * because they will miss recent referenced history.
> + */
> + test_and_clear_page_young(page);
> + deactivate_page(page);
> + }
> +
> + arch_enter_lazy_mmu_mode();
Did you mean to say arch_leave_lazy_mmu_mode() ?
> + 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 cold_walk = {
> + .pmd_entry = madvise_cold_pte_range,
> + .mm = vma->vm_mm,
> + .private = tlb,
> + };
> +
> + tlb_start_vma(tlb, vma);
> + walk_page_range(addr, end, &cold_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 +692,7 @@ 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 +714,7 @@ 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 +868,8 @@ 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 +891,7 @@ 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 95872bdfec4e..c8f0ec6b0e80 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -523,7 +523,7 @@ 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 55899c1f54af..b501ad6eb091 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 +539,22 @@ 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);
> + 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 +607,10 @@ 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 +644,26 @@ 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 +728,7 @@ 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);
> --
> 2.22.0.510.g264f2c817a-goog
>
