Hi Joel,
On Tue, Jun 04, 2019 at 04:38:41PM -0400, Joel Fernandes wrote:
> 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 <minc...@kernel.org>
> > ---
> > 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.
ptep_test_and_clear_young doesn't change PG_idle/young so idle page tracking
doesn't affect.
>
> 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 will remove PG_young bit so that the page will be reclaimed.
Do I miss your point?
>
> > + 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?
clear_refs couldn't find the access any longer. However, it's the
intention because we couldn't reclaim the page without it.
>
> 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.
Okay, I will add some comment.
Thanks.
