On 07/08/2014 02:03 PM, Minchan Kim wrote: > Linux doesn't have an ability to free pages lazy while other OS > already have been supported that named by madvise(MADV_FREE). > > The gain is clear that kernel can discard freed pages rather than > swapping out or OOM if memory pressure happens. > > Without memory pressure, freed pages would be reused by userspace > without another additional overhead(ex, page fault + allocation > + zeroing). > > How to work is following as. > > When madvise syscall is called, VM clears dirty bit of ptes of > the range. If memory pressure happens, VM checks dirty bit of > page table and if it found still "clean", it means it's a > "lazyfree pages" so VM could discard the page instead of swapping out. > Once there was store operation for the page before VM peek a page > to reclaim, dirty bit is set so VM can swap out the page instead of > discarding. > > Firstly, heavy users would be general allocators(ex, jemalloc, > tcmalloc and hope glibc supports it) and jemalloc/tcmalloc already > have supported the feature for other OS(ex, FreeBSD) > > barrios@blaptop:~/benchmark/ebizzy$ lscpu > Architecture: x86_64 > CPU op-mode(s): 32-bit, 64-bit > Byte Order: Little Endian > CPU(s): 4 > On-line CPU(s) list: 0-3 > Thread(s) per core: 2 > Core(s) per socket: 2 > Socket(s): 1 > NUMA node(s): 1 > Vendor ID: GenuineIntel > CPU family: 6 > Model: 42 > Stepping: 7 > CPU MHz: 2801.000 > BogoMIPS: 5581.64 > Virtualization: VT-x > L1d cache: 32K > L1i cache: 32K > L2 cache: 256K > L3 cache: 4096K > NUMA node0 CPU(s): 0-3 > > ebizzy benchmark(./ebizzy -S 10 -n 512) > > vanilla-jemalloc MADV_free-jemalloc > > 1 thread > records: 10 records: 10 > avg: 7682.10 avg: 15306.10 > std: 62.35(0.81%) std: 347.99(2.27%) > max: 7770.00 max: 15622.00 > min: 7598.00 min: 14772.00 > > 2 thread > records: 10 records: 10 > avg: 12747.50 avg: 24171.00 > std: 792.06(6.21%) std: 895.18(3.70%) > max: 13337.00 max: 26023.00 > min: 10535.00 min: 23152.00 > > 4 thread > records: 10 records: 10 > avg: 16474.60 avg: 33717.90 > std: 1496.45(9.08%) std: 2008.97(5.96%) > max: 17877.00 max: 35958.00 > min: 12224.00 min: 29565.00 > > 8 thread > records: 10 records: 10 > avg: 16778.50 avg: 33308.10 > std: 825.53(4.92%) std: 1668.30(5.01%) > max: 17543.00 max: 36010.00 > min: 14576.00 min: 29577.00 > > 16 thread > records: 10 records: 10 > avg: 20614.40 avg: 35516.30 > std: 602.95(2.92%) std: 1283.65(3.61%) > max: 21753.00 max: 37178.00 > min: 19605.00 min: 33217.00 > > 32 thread > records: 10 records: 10 > avg: 22771.70 avg: 36018.50 > std: 598.94(2.63%) std: 1046.76(2.91%) > max: 24035.00 max: 37266.00 > min: 22108.00 min: 34149.00 > > In summary, MADV_FREE is about 2 time faster than MADV_DONTNEED. > > Cc: Michael Kerrisk <mtk.manpages@xxxxxxxxx> > Cc: Linux API <linux-api@xxxxxxxxxxxxxxx> > Cc: Hugh Dickins <hughd@xxxxxxxxxx> > Cc: Johannes Weiner <hannes@xxxxxxxxxxx> > Cc: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx> > Cc: Mel Gorman <mgorman@xxxxxxx> > Cc: Jason Evans <je@xxxxxx> > Cc: Zhang Yanfei <zhangyanfei@xxxxxxxxxxxxxx> > Acked-by: Rik van Riel <riel@xxxxxxxxxx> > Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx> A quick respin, looks good to me now for this !THP part. And looks neat with the Pagewalker. Acked-by: Zhang Yanfei <zhangyanfei@xxxxxxxxxxxxxx> > --- > include/linux/rmap.h | 9 ++- > include/linux/vm_event_item.h | 1 + > include/uapi/asm-generic/mman-common.h | 1 + > mm/madvise.c | 135 +++++++++++++++++++++++++++++++++ > mm/rmap.c | 42 +++++++++- > mm/vmscan.c | 40 ++++++++-- > mm/vmstat.c | 1 + > 7 files changed, 217 insertions(+), 12 deletions(-) > > diff --git a/include/linux/rmap.h b/include/linux/rmap.h > index be574506e6a9..0ba377b97a38 100644 > --- a/include/linux/rmap.h > +++ b/include/linux/rmap.h > @@ -75,6 +75,7 @@ enum ttu_flags { > TTU_UNMAP = 1, /* unmap mode */ > TTU_MIGRATION = 2, /* migration mode */ > TTU_MUNLOCK = 4, /* munlock mode */ > + TTU_FREE = 8, /* free mode */ > > TTU_IGNORE_MLOCK = (1 << 8), /* ignore mlock */ > TTU_IGNORE_ACCESS = (1 << 9), /* don't age */ > @@ -181,7 +182,8 @@ static inline void page_dup_rmap(struct page *page) > * Called from mm/vmscan.c to handle paging out > */ > int page_referenced(struct page *, int is_locked, > - struct mem_cgroup *memcg, unsigned long *vm_flags); > + struct mem_cgroup *memcg, unsigned long *vm_flags, > + int *is_dirty); > > #define TTU_ACTION(x) ((x) & TTU_ACTION_MASK) > > @@ -260,9 +262,12 @@ int rmap_walk(struct page *page, struct rmap_walk_control *rwc); > > static inline int page_referenced(struct page *page, int is_locked, > struct mem_cgroup *memcg, > - unsigned long *vm_flags) > + unsigned long *vm_flags, > + int *is_pte_dirty) > { > *vm_flags = 0; > + if (is_pte_dirty) > + *is_pte_dirty = 0; > return 0; > } > > diff --git a/include/linux/vm_event_item.h b/include/linux/vm_event_item.h > index ced92345c963..e2d3fb1e9814 100644 > --- a/include/linux/vm_event_item.h > +++ b/include/linux/vm_event_item.h > @@ -25,6 +25,7 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT, > FOR_ALL_ZONES(PGALLOC), > PGFREE, PGACTIVATE, PGDEACTIVATE, > PGFAULT, PGMAJFAULT, > + PGLAZYFREED, > FOR_ALL_ZONES(PGREFILL), > FOR_ALL_ZONES(PGSTEAL_KSWAPD), > FOR_ALL_ZONES(PGSTEAL_DIRECT), > diff --git a/include/uapi/asm-generic/mman-common.h b/include/uapi/asm-generic/mman-common.h > index ddc3b36f1046..7a94102b7a02 100644 > --- a/include/uapi/asm-generic/mman-common.h > +++ b/include/uapi/asm-generic/mman-common.h > @@ -34,6 +34,7 @@ > #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_FREE 5 /* free pages only if memory pressure */ > > /* common parameters: try to keep these consistent across architectures */ > #define MADV_REMOVE 9 /* remove these pages & resources */ > diff --git a/mm/madvise.c b/mm/madvise.c > index 0938b30da4ab..a6aa7d4c4e02 100644 > --- a/mm/madvise.c > +++ b/mm/madvise.c > @@ -19,6 +19,14 @@ > #include <linux/blkdev.h> > #include <linux/swap.h> > #include <linux/swapops.h> > +#include <linux/mmu_notifier.h> > + > +#include <asm/tlb.h> > + > +struct madvise_free_private { > + struct vm_area_struct *vma; > + struct mmu_gather *tlb; > +}; > > /* > * Any behaviour which results in changes to the vma->vm_flags needs to > @@ -31,6 +39,7 @@ static int madvise_need_mmap_write(int behavior) > case MADV_REMOVE: > case MADV_WILLNEED: > case MADV_DONTNEED: > + case MADV_FREE: > return 0; > default: > /* be safe, default to 1. list exceptions explicitly */ > @@ -251,6 +260,124 @@ static long madvise_willneed(struct vm_area_struct *vma, > return 0; > } > > +static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr, > + unsigned long end, struct mm_walk *walk) > + > +{ > + struct madvise_free_private *fp = walk->private; > + struct mmu_gather *tlb = fp->tlb; > + struct mm_struct *mm = tlb->mm; > + struct vm_area_struct *vma = fp->vma; > + spinlock_t *ptl; > + pte_t *pte, ptent; > + struct page *page; > + > + split_huge_page_pmd(vma, addr, pmd); > + if (pmd_trans_unstable(pmd)) > + return 0; > + > + pte = pte_offset_map_lock(mm, pmd, addr, &ptl); > + 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 && PageSwapCache(page)) { > + if (trylock_page(page)) { > + if (try_to_free_swap(page)) > + ClearPageDirty(page); > + unlock_page(page); > + } else > + continue; > + } > + > + /* > + * Some of architecture(ex, PPC) don't update TLB > + * with set_pte_at and tlb_remove_tlb_entry so for > + * the portability, remap the pte with old|clean > + * after pte clearing. > + */ > + ptent = ptep_get_and_clear_full(mm, addr, pte, > + tlb->fullmm); > + ptent = pte_mkold(ptent); > + ptent = pte_mkclean(ptent); > + set_pte_at(mm, addr, pte, ptent); > + tlb_remove_tlb_entry(tlb, pte, addr); > + } > + arch_leave_lazy_mmu_mode(); > + pte_unmap_unlock(pte - 1, ptl); > + cond_resched(); > + return 0; > +} > + > +static void madvise_free_page_range(struct mmu_gather *tlb, > + struct vm_area_struct *vma, > + unsigned long addr, unsigned long end) > +{ > + struct madvise_free_private fp = { > + .vma = vma, > + .tlb = tlb, > + }; > + > + struct mm_walk free_walk = { > + .pmd_entry = madvise_free_pte_range, > + .mm = vma->vm_mm, > + .private = &fp, > + }; > + > + BUG_ON(addr >= end); > + tlb_start_vma(tlb, vma); > + walk_page_range(addr, end, &free_walk); > + tlb_end_vma(tlb, vma); > +} > + > +static int madvise_free_single_vma(struct vm_area_struct *vma, > + unsigned long start_addr, unsigned long end_addr) > +{ > + unsigned long start, end; > + struct mm_struct *mm = vma->vm_mm; > + struct mmu_gather tlb; > + > + if (vma->vm_flags & (VM_LOCKED|VM_HUGETLB|VM_PFNMAP)) > + return -EINVAL; > + > + /* MADV_FREE works for only anon vma at the moment */ > + if (vma->vm_file) > + return -EINVAL; > + > + start = max(vma->vm_start, start_addr); > + if (start >= vma->vm_end) > + return -EINVAL; > + end = min(vma->vm_end, end_addr); > + if (end <= vma->vm_start) > + return -EINVAL; > + > + lru_add_drain(); > + tlb_gather_mmu(&tlb, mm, start, end); > + update_hiwater_rss(mm); > + > + mmu_notifier_invalidate_range_start(mm, start, end); > + madvise_free_page_range(&tlb, vma, start, end); > + mmu_notifier_invalidate_range_end(mm, start, end); > + tlb_finish_mmu(&tlb, start, end); > + > + return 0; > +} > + > +static long madvise_free(struct vm_area_struct *vma, > + struct vm_area_struct **prev, > + unsigned long start, unsigned long end) > +{ > + *prev = vma; > + return madvise_free_single_vma(vma, start, end); > +} > + > /* > * Application no longer needs these pages. If the pages are dirty, > * it's OK to just throw them away. The app will be more careful about > @@ -381,6 +508,13 @@ 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_FREE: > + /* > + * XXX: In this implementation, MADV_FREE works like > + * MADV_DONTNEED on swapless system or full swap. > + */ > + if (get_nr_swap_pages() > 0) > + return madvise_free(vma, prev, start, end); > case MADV_DONTNEED: > return madvise_dontneed(vma, prev, start, end); > default: > @@ -400,6 +534,7 @@ madvise_behavior_valid(int behavior) > case MADV_REMOVE: > case MADV_WILLNEED: > case MADV_DONTNEED: > + case MADV_FREE: > #ifdef CONFIG_KSM > case MADV_MERGEABLE: > case MADV_UNMERGEABLE: > diff --git a/mm/rmap.c b/mm/rmap.c > index 7928ddd91b6e..a8e34596dc97 100644 > --- a/mm/rmap.c > +++ b/mm/rmap.c > @@ -663,6 +663,7 @@ int page_mapped_in_vma(struct page *page, struct vm_area_struct *vma) > } > > struct page_referenced_arg { > + int dirtied; > int mapcount; > int referenced; > unsigned long vm_flags; > @@ -677,6 +678,7 @@ static int page_referenced_one(struct page *page, struct vm_area_struct *vma, > struct mm_struct *mm = vma->vm_mm; > spinlock_t *ptl; > int referenced = 0; > + int dirty = 0; > struct page_referenced_arg *pra = arg; > > if (unlikely(PageTransHuge(page))) { > @@ -700,6 +702,11 @@ static int page_referenced_one(struct page *page, struct vm_area_struct *vma, > /* go ahead even if the pmd is pmd_trans_splitting() */ > if (pmdp_clear_flush_young_notify(vma, address, pmd)) > referenced++; > + > + /* > + * In this implmentation, MADV_FREE doesn't support THP free > + */ > + dirty++; > spin_unlock(ptl); > } else { > pte_t *pte; > @@ -729,6 +736,10 @@ static int page_referenced_one(struct page *page, struct vm_area_struct *vma, > if (likely(!(vma->vm_flags & VM_SEQ_READ))) > referenced++; > } > + > + if (pte_dirty(*pte)) > + dirty++; > + > pte_unmap_unlock(pte, ptl); > } > > @@ -737,6 +748,9 @@ static int page_referenced_one(struct page *page, struct vm_area_struct *vma, > pra->vm_flags |= vma->vm_flags; > } > > + if (dirty) > + pra->dirtied++; > + > pra->mapcount--; > if (!pra->mapcount) > return SWAP_SUCCESS; /* To break the loop */ > @@ -761,6 +775,7 @@ static bool invalid_page_referenced_vma(struct vm_area_struct *vma, void *arg) > * @is_locked: caller holds lock on the page > * @memcg: target memory cgroup > * @vm_flags: collect encountered vma->vm_flags who actually referenced the page > + * @is_pte_dirty: ptes which have marked dirty bit - used for lazyfree page > * > * Quick test_and_clear_referenced for all mappings to a page, > * returns the number of ptes which referenced the page. > @@ -768,7 +783,8 @@ static bool invalid_page_referenced_vma(struct vm_area_struct *vma, void *arg) > int page_referenced(struct page *page, > int is_locked, > struct mem_cgroup *memcg, > - unsigned long *vm_flags) > + unsigned long *vm_flags, > + int *is_pte_dirty) > { > int ret; > int we_locked = 0; > @@ -783,6 +799,9 @@ int page_referenced(struct page *page, > }; > > *vm_flags = 0; > + if (is_pte_dirty) > + *is_pte_dirty = 0; > + > if (!page_mapped(page)) > return 0; > > @@ -810,6 +829,9 @@ int page_referenced(struct page *page, > if (we_locked) > unlock_page(page); > > + if (is_pte_dirty) > + *is_pte_dirty = pra.dirtied; > + > return pra.referenced; > } > > @@ -1128,6 +1150,7 @@ static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma, > spinlock_t *ptl; > int ret = SWAP_AGAIN; > enum ttu_flags flags = (enum ttu_flags)arg; > + int dirty = 0; > > pte = page_check_address(page, mm, address, &ptl, 0); > if (!pte) > @@ -1157,7 +1180,8 @@ static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma, > pteval = ptep_clear_flush(vma, address, pte); > > /* Move the dirty bit to the physical page now the pte is gone. */ > - if (pte_dirty(pteval)) > + dirty = pte_dirty(pteval); > + if (dirty) > set_page_dirty(page); > > /* Update high watermark before we lower rss */ > @@ -1186,6 +1210,19 @@ static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma, > swp_entry_t entry = { .val = page_private(page) }; > pte_t swp_pte; > > + if (flags & TTU_FREE) { > + VM_BUG_ON_PAGE(PageSwapCache(page), page); > + if (dirty || PageDirty(page)) { > + set_pte_at(mm, address, pte, pteval); > + ret = SWAP_FAIL; > + goto out_unmap; > + } else { > + /* It's a freeable page by MADV_FREE */ > + dec_mm_counter(mm, MM_ANONPAGES); > + goto discard; > + } > + } > + > if (PageSwapCache(page)) { > /* > * Store the swap location in the pte. > @@ -1227,6 +1264,7 @@ static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma, > } else > dec_mm_counter(mm, MM_FILEPAGES); > > +discard: > page_remove_rmap(page); > page_cache_release(page); > > diff --git a/mm/vmscan.c b/mm/vmscan.c > index 6d24fd63b209..d88413ccadcc 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -707,13 +707,17 @@ enum page_references { > }; > > static enum page_references page_check_references(struct page *page, > - struct scan_control *sc) > + struct scan_control *sc, > + bool *freeable) > { > int referenced_ptes, referenced_page; > unsigned long vm_flags; > + int pte_dirty; > + > + VM_BUG_ON_PAGE(!PageLocked(page), page); > > referenced_ptes = page_referenced(page, 1, sc->target_mem_cgroup, > - &vm_flags); > + &vm_flags, &pte_dirty); > referenced_page = TestClearPageReferenced(page); > > /* > @@ -754,6 +758,10 @@ static enum page_references page_check_references(struct page *page, > return PAGEREF_KEEP; > } > > + if (PageAnon(page) && !pte_dirty && !PageSwapCache(page) && > + !PageDirty(page)) > + *freeable = true; > + > /* Reclaim if clean, defer dirty pages to writeback */ > if (referenced_page && !PageSwapBacked(page)) > return PAGEREF_RECLAIM_CLEAN; > @@ -823,6 +831,7 @@ static unsigned long shrink_page_list(struct list_head *page_list, > int may_enter_fs; > enum page_references references = PAGEREF_RECLAIM_CLEAN; > bool dirty, writeback; > + bool freeable = false; > > cond_resched(); > > @@ -945,7 +954,8 @@ static unsigned long shrink_page_list(struct list_head *page_list, > } > > if (!force_reclaim) > - references = page_check_references(page, sc); > + references = page_check_references(page, sc, > + &freeable); > > switch (references) { > case PAGEREF_ACTIVATE: > @@ -961,7 +971,7 @@ static unsigned long shrink_page_list(struct list_head *page_list, > * Anonymous process memory has backing store? > * Try to allocate it some swap space here. > */ > - if (PageAnon(page) && !PageSwapCache(page)) { > + if (PageAnon(page) && !PageSwapCache(page) && !freeable) { > if (!(sc->gfp_mask & __GFP_IO)) > goto keep_locked; > if (!add_to_swap(page, page_list)) > @@ -976,8 +986,9 @@ static unsigned long shrink_page_list(struct list_head *page_list, > * The page is mapped into the page tables of one or more > * processes. Try to unmap it here. > */ > - if (page_mapped(page) && mapping) { > - switch (try_to_unmap(page, ttu_flags)) { > + if (page_mapped(page) && (mapping || freeable)) { > + switch (try_to_unmap(page, ttu_flags | > + (freeable ? TTU_FREE : 0))) { > case SWAP_FAIL: > goto activate_locked; > case SWAP_AGAIN: > @@ -985,7 +996,20 @@ static unsigned long shrink_page_list(struct list_head *page_list, > case SWAP_MLOCK: > goto cull_mlocked; > case SWAP_SUCCESS: > - ; /* try to free the page below */ > + /* try to free the page below */ > + if (!freeable) > + break; > + /* > + * Freeable anon page doesn't have mapping > + * due to skipping of swapcache so we free > + * page in here rather than __remove_mapping. > + */ > + VM_BUG_ON_PAGE(PageSwapCache(page), page); > + if (!page_freeze_refs(page, 1)) > + goto keep_locked; > + __clear_page_locked(page); > + count_vm_event(PGLAZYFREED); > + goto free_it; > } > } > > @@ -1727,7 +1751,7 @@ static void shrink_active_list(unsigned long nr_to_scan, > } > > if (page_referenced(page, 0, sc->target_mem_cgroup, > - &vm_flags)) { > + &vm_flags, NULL)) { > nr_rotated += hpage_nr_pages(page); > /* > * Identify referenced, file-backed active pages and > diff --git a/mm/vmstat.c b/mm/vmstat.c > index eef6321c8470..da18337c6c66 100644 > --- a/mm/vmstat.c > +++ b/mm/vmstat.c > @@ -794,6 +794,7 @@ const char * const vmstat_text[] = { > > "pgfault", > "pgmajfault", > + "pglazyfreed", > > TEXTS_FOR_ZONES("pgrefill") > TEXTS_FOR_ZONES("pgsteal_kswapd") > -- Thanks. Zhang Yanfei -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx"> email@xxxxxxxxx </a>