On Mon, Jun 03, 2019 at 02:36:52PM +0900, Minchan Kim 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
> 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);
Wondering here how it interacts with idle page tracking. Here since young
flag is cleared by the cold hint, page_referenced_one() or
page_idle_clear_pte_refs_one() will not be able to clear the page-idle flag
if it was previously set since it does not know any more that a page was
actively referenced.
Should you also be clearing the page-idle flag here if the ptep young/accessed
bit was previously set, just so that page-idle tracking works smoothly when
this hint is concurrently applied?
> + 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);
I was curious, how does the above interact with clear_refs?
It appears that a range that is marked as cold will appear to be unreferenced
(since referenced flag is cleared) even though it may have been referenced in
the past. Very least, I believe this behavior should be documented somewhere.
I believe it is best for us to make the clear_refs technique behave similar
to the idle-page tracking for the purposes of figuring out which pages are
referenced, so that clear_refs is more immune to this hint.
thanks,
- Joel
