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SubjectRe: [PATCH v3] support madvise(MADV_FREE)
Hello Minchan,

Nice work. It seems I forgot to reply your mail in the first RFC version
of the patch, so I just review this new one.

On 04/07/2014 10:51 AM, 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).

Just from this, I cannot see how you handle the 'lazyfree' pages and
how to distinguish 'lazyfree' and 'nonlazyfree' pages. Anyway, I've
known these from the patch itself, so I know them, but it is difficult
for someone who wants to get the knowledge from the log. So could you
add a little explanation into this log to help understanding the code,
especially you have put all the changes into one patch?

>
> 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: 7436.70 avg: 15292.70
> std: 48.01(0.65%) std: 496.40(3.25%)
> max: 7542.00 max: 15944.00
> min: 7366.00 min: 14478.00
>
> 2 thread
> records: 10 records: 10
> avg: 12190.50 avg: 24975.50
> std: 1011.51(8.30%) std: 1127.22(4.51%)
> max: 13012.00 max: 26382.00
> min: 10192.00 min: 23265.00
>
> 4 thread
> records: 10 records: 10
> avg: 16875.30 avg: 36320.90
> std: 562.59(3.33%) std: 1503.75(4.14%)
> max: 17465.00 max: 38314.00
> min: 15552.00 min: 33863.00
>
> 8 thread
> records: 10 records: 10
> avg: 16966.80 avg: 35915.20
> std: 229.35(1.35%) std: 2153.89(6.00%)
> max: 17456.00 max: 37943.00
> min: 16742.00 min: 29891.00
>
> 16 thread
> records: 10 records: 10
> avg: 20590.90 avg: 37388.40
> std: 362.33(1.76%) std: 1282.59(3.43%)
> max: 20954.00 max: 38911.00
> min: 19985.00 min: 34928.00
>
> 32 thread
> records: 10 records: 10
> avg: 22633.40 avg: 37118.00
> std: 413.73(1.83%) std: 766.36(2.06%)
> max: 23120.00 max: 38328.00
> min: 22071.00 min: 35557.00
>
> In summary, MADV_FREE is about 2 time faster than MADV_DONTNEED.
>
> Patchset is based on 3.14
>
> * From v2
> * Remove forceful dirty marking of swap-readed page - Johannes
> * Remove deactivation logic of lazyfreed page
> * Rebased on 3.14
> * Remove RFC tag
>
> * From v1
> * Use custom page table walker for madvise_free - Johannes
> * Remove PG_lazypage flag - Johannes
> * Do madvise_dontneed instead of madvise_freein swapless system
>
> Cc: Hugh Dickins <hughd@google.com>
> Cc: Johannes Weiner <hannes@cmpxchg.org>
> Cc: Rik van Riel <riel@redhat.com>
> Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
> Cc: Mel Gorman <mgorman@suse.de>
> Cc: Jason Evans <je@fb.com>
> Signed-off-by: Minchan Kim <minchan@kernel.org>
> ---
> include/linux/mm.h | 2 +
> include/linux/rmap.h | 14 +++-
> include/linux/vm_event_item.h | 1 +
> include/uapi/asm-generic/mman-common.h | 1 +
> mm/madvise.c | 25 ++++++
> mm/memory.c | 141 +++++++++++++++++++++++++++++++++
> mm/rmap.c | 62 +++++++++++++--
> mm/vmscan.c | 30 ++++++-
> mm/vmstat.c | 1 +
> 9 files changed, 267 insertions(+), 10 deletions(-)
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index c1b7414c7bef..79af90212c19 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -1063,6 +1063,8 @@ int zap_vma_ptes(struct vm_area_struct *vma, unsigned long address,
> unsigned long size);
> void zap_page_range(struct vm_area_struct *vma, unsigned long address,
> unsigned long size, struct zap_details *);
> +void lazyfree_range(struct vm_area_struct *vma, unsigned long address,
> + unsigned long size);
> void unmap_vmas(struct mmu_gather *tlb, struct vm_area_struct *start_vma,
> unsigned long start, unsigned long end);
>
> diff --git a/include/linux/rmap.h b/include/linux/rmap.h
> index b66c2110cb1f..1f3517027ffa 100644
> --- a/include/linux/rmap.h
> +++ b/include/linux/rmap.h
> @@ -182,7 +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);
> int page_referenced_one(struct page *, struct vm_area_struct *,
> unsigned long address, void *arg);
>
> @@ -235,6 +236,11 @@ struct anon_vma *page_lock_anon_vma_read(struct page *page);
> void page_unlock_anon_vma_read(struct anon_vma *anon_vma);
> int page_mapped_in_vma(struct page *page, struct vm_area_struct *vma);
>
> +struct rmap_private {
> + enum ttu_flags flags;
> + int pte_dirty; /* used for lazyfree */
> +};
> +
> /*
> * rmap_walk_control: To control rmap traversing for specific needs
> *
> @@ -265,9 +271,12 @@ 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;
> }
>
> @@ -288,5 +297,6 @@ static inline int page_mkclean(struct page *page)
> #define SWAP_AGAIN 1
> #define SWAP_FAIL 2
> #define SWAP_MLOCK 3
> +#define SWAP_DISCARD 4
>
> #endif /* _LINUX_RMAP_H */
> diff --git a/include/linux/vm_event_item.h b/include/linux/vm_event_item.h
> index 3a712e2e7d76..a69680d335bb 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 4164529a94f9..b7eedd33ebab 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 539eeb96b323..4a2aa96b2db3 100644
> --- a/mm/madvise.c
> +++ b/mm/madvise.c
> @@ -31,6 +31,7 @@ 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 +252,22 @@ static long madvise_willneed(struct vm_area_struct *vma,
> return 0;
> }
>
> +static long madvise_lazyfree(struct vm_area_struct *vma,
> + struct vm_area_struct **prev,
> + unsigned long start, unsigned long end)
> +{
> + *prev = vma;
> + 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;
> +
> + lazyfree_range(vma, start, end - start);
> + return 0;
> +}
> +
> /*
> * 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
> @@ -384,6 +401,13 @@ 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:
> + /*
> + * In this implementation, MADV_FREE works like MADV_DONTNEED
> + * on swapless system or full swap.
> + */
> + if (get_nr_swap_pages() > 0)
> + return madvise_lazyfree(vma, prev, start, end);
> case MADV_DONTNEED:
> return madvise_dontneed(vma, prev, start, end);
> default:
> @@ -403,6 +427,7 @@ 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/memory.c b/mm/memory.c
> index 22dfa617bddb..7811faa8bbe3 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -1268,6 +1268,105 @@ static inline unsigned long zap_pud_range(struct mmu_gather *tlb,
> return addr;
> }
>
> +static unsigned long lazyfree_pte_range(struct mmu_gather *tlb,
> + struct vm_area_struct *vma, pmd_t *pmd,
> + unsigned long addr, unsigned long end)
> +{
> + struct mm_struct *mm = tlb->mm;
> + spinlock_t *ptl;
> + pte_t *start_pte;
> + pte_t *pte;
> +
> + start_pte = pte_offset_map_lock(mm, pmd, addr, &ptl);
> + pte = start_pte;
> + arch_enter_lazy_mmu_mode();
> + do {
> + pte_t ptent = *pte;
> +
> + if (pte_none(ptent))
> + continue;
> +
> + if (!pte_present(ptent))
> + continue;
> +
> + ptent = pte_mkold(ptent);
> + ptent = pte_mkclean(ptent);
> + set_pte_at(mm, addr, pte, ptent);
> + tlb_remove_tlb_entry(tlb, pte, addr);
> + } while (pte++, addr += PAGE_SIZE, addr != end);
> + arch_leave_lazy_mmu_mode();
> + pte_unmap_unlock(start_pte, ptl);
> +
> + return addr;
> +}
> +
> +static inline unsigned long lazyfree_pmd_range(struct mmu_gather *tlb,
> + struct vm_area_struct *vma, pud_t *pud,
> + unsigned long addr, unsigned long end)
> +{
> + pmd_t *pmd;
> + unsigned long next;
> +
> + pmd = pmd_offset(pud, addr);
> + do {
> + next = pmd_addr_end(addr, end);
> + /* TODO : optimize */
> + if (pmd_trans_huge(*pmd))
> + split_huge_page_pmd(vma, addr, pmd);
> + /*
> + * Here there can be other concurrent MADV_DONTNEED or
> + * trans huge page faults running, and if the pmd is
> + * none or trans huge it can change under us. This is
> + * because MADV_LAZYFREE holds the mmap_sem in read
> + * mode.
> + */
> + if (pmd_none_or_trans_huge_or_clear_bad(pmd))
> + goto next;
> + next = lazyfree_pte_range(tlb, vma, pmd, addr, next);
> +next:
> + cond_resched();
> + } while (pmd++, addr = next, addr != end);
> +
> + return addr;
> +}
> +
> +static inline unsigned long lazyfree_pud_range(struct mmu_gather *tlb,
> + struct vm_area_struct *vma, pgd_t *pgd,
> + unsigned long addr, unsigned long end)
> +{
> + pud_t *pud;
> + unsigned long next;
> +
> + pud = pud_offset(pgd, addr);
> + do {
> + next = pud_addr_end(addr, end);
> + if (pud_none_or_clear_bad(pud))
> + continue;
> + next = lazyfree_pmd_range(tlb, vma, pud, addr, next);
> + } while (pud++, addr = next, addr != end);
> +
> + return addr;
> +}
> +
> +static void lazyfree_page_range(struct mmu_gather *tlb,
> + struct vm_area_struct *vma,
> + unsigned long addr, unsigned long end)
> +{
> + pgd_t *pgd;
> + unsigned long next;
> +
> + BUG_ON(addr >= end);
> + tlb_start_vma(tlb, vma);
> + pgd = pgd_offset(vma->vm_mm, addr);
> + do {
> + next = pgd_addr_end(addr, end);
> + if (pgd_none_or_clear_bad(pgd))
> + continue;
> + next = lazyfree_pud_range(tlb, vma, pgd, addr, next);
> + } while (pgd++, addr = next, addr != end);
> + tlb_end_vma(tlb, vma);
> +}
> +
> static void unmap_page_range(struct mmu_gather *tlb,
> struct vm_area_struct *vma,
> unsigned long addr, unsigned long end,
> @@ -1294,6 +1393,23 @@ static void unmap_page_range(struct mmu_gather *tlb,
> }
>
>
> +static void lazyfree_single_vma(struct mmu_gather *tlb,
> + struct vm_area_struct *vma, unsigned long start_addr,
> + unsigned long end_addr)
> +{
> + unsigned long start = max(vma->vm_start, start_addr);
> + unsigned long end;
> +
> + if (start >= vma->vm_end)
> + return;
> + end = min(vma->vm_end, end_addr);
> + if (end <= vma->vm_start)
> + return;
> +
> + if (start != end)
> + lazyfree_page_range(tlb, vma, start, end);
> +}
> +
> static void unmap_single_vma(struct mmu_gather *tlb,
> struct vm_area_struct *vma, unsigned long start_addr,
> unsigned long end_addr,
> @@ -1368,6 +1484,31 @@ void unmap_vmas(struct mmu_gather *tlb,
> }
>
> /**
> + * lazyfree_range - clear dirty bit of pte in a given range
> + * @vma: vm_area_struct holding the applicable pages
> + * @start: starting address of pages
> + * @size: number of bytes to do lazyfree
> + *
> + * Caller must protect the VMA list
> + */
> +void lazyfree_range(struct vm_area_struct *vma, unsigned long start,
> + unsigned long size)
> +{
> + struct mm_struct *mm = vma->vm_mm;
> + struct mmu_gather tlb;
> + unsigned long end = start + size;
> +
> + lru_add_drain();
> + tlb_gather_mmu(&tlb, mm, start, end);
> + update_hiwater_rss(mm);
> + mmu_notifier_invalidate_range_start(mm, start, end);
> + for ( ; vma && vma->vm_start < end; vma = vma->vm_next)
> + lazyfree_single_vma(&tlb, vma, start, end);
> + mmu_notifier_invalidate_range_end(mm, start, end);
> + tlb_finish_mmu(&tlb, start, end);
> +}
> +
> +/**
> * zap_page_range - remove user pages in a given range
> * @vma: vm_area_struct holding the applicable pages
> * @start: starting address of pages to zap
> diff --git a/mm/rmap.c b/mm/rmap.c
> index 8fc049f9a5a6..ca0ebd28edfa 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -661,6 +661,7 @@ 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;
> @@ -675,6 +676,7 @@ 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))) {
> @@ -727,6 +729,10 @@ 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);
> }
>
> @@ -735,6 +741,9 @@ 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 */
> @@ -759,6 +768,7 @@ 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
> *
> * Quick test_and_clear_referenced for all mappings to a page,
> * returns the number of ptes which referenced the page.
> @@ -766,7 +776,8 @@ 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;
> @@ -781,6 +792,9 @@ int page_referenced(struct page *page,
> };
>
> *vm_flags = 0;
> + if (is_pte_dirty)
> + *is_pte_dirty = 0;
> +
> if (!page_mapped(page))
> return 0;
>
> @@ -808,6 +822,9 @@ int page_referenced(struct page *page,
> if (we_locked)
> unlock_page(page);
>
> + if (is_pte_dirty)
> + *is_pte_dirty = pra.dirtied;
> +
> return pra.referenced;
> }
>
> @@ -1120,7 +1137,9 @@ int try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
> pte_t pteval;
> spinlock_t *ptl;
> int ret = SWAP_AGAIN;
> - enum ttu_flags flags = (enum ttu_flags)arg;
> + struct rmap_private *rp = (struct rmap_private *)arg;
> + enum ttu_flags flags = rp->flags;
> + int dirty = 0;
>
> pte = page_check_address(page, mm, address, &ptl, 0);
> if (!pte)
> @@ -1150,7 +1169,8 @@ 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 */
> @@ -1169,6 +1189,15 @@ 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 ((TTU_ACTION(flags) == TTU_UNMAP) && !dirty &&
> + !PageSwapCache(page) && !PageDirty(page)) {

I see this
!dirty && !PageSwapCache(page) && !PageDirty(page)
test in several places, could be placed into a inline function with a
appropriate name?


> + dec_mm_counter(mm, MM_ANONPAGES);
> + goto discard;
> + }
> +
> + if (dirty)
> + rp->pte_dirty++;
> +
> if (PageSwapCache(page)) {
> /*
> * Store the swap location in the pte.
> @@ -1187,6 +1216,10 @@ int try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
> }
> dec_mm_counter(mm, MM_ANONPAGES);
> inc_mm_counter(mm, MM_SWAPENTS);
> + } else if (TTU_ACTION(flags) == TTU_UNMAP) {
> + set_pte_at(mm, address, pte, pteval);
> + ret = SWAP_FAIL;
> + goto out_unmap;

Can you elaborate this chage a bit?

> } else if (IS_ENABLED(CONFIG_MIGRATION)) {
> /*
> * Store the pfn of the page in a special migration
> @@ -1210,6 +1243,7 @@ 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);
>
> @@ -1470,13 +1504,19 @@ static int page_not_mapped(struct page *page)
> * SWAP_AGAIN - we missed a mapping, try again later
> * SWAP_FAIL - the page is unswappable
> * SWAP_MLOCK - page is mlocked.
> + * SWAP_DISCARD - same with SWAP_SUCCESS but no need to swap out
> */
> int try_to_unmap(struct page *page, enum ttu_flags flags)
> {
> int ret;
> +
> + struct rmap_private rp = {
> + .flags = flags,
> + };
> +
> struct rmap_walk_control rwc = {
> .rmap_one = try_to_unmap_one,
> - .arg = (void *)flags,
> + .arg = &rp,
> .done = page_not_mapped,
> .file_nonlinear = try_to_unmap_nonlinear,
> .anon_lock = page_lock_anon_vma_read,
> @@ -1497,8 +1537,14 @@ int try_to_unmap(struct page *page, enum ttu_flags flags)
>
> ret = rmap_walk(page, &rwc);
>
> - if (ret != SWAP_MLOCK && !page_mapped(page))
> + if (ret != SWAP_MLOCK && !page_mapped(page)) {
> ret = SWAP_SUCCESS;
> + if (TTU_ACTION(flags) == TTU_UNMAP && !rp.pte_dirty &&
> + PageAnon(page) && !PageSwapCache(page) &&
> + !PageDirty(page) && !PageKsm(page))
> + ret = SWAP_DISCARD;
> + }
> +
> return ret;
> }
>
> @@ -1520,9 +1566,13 @@ int try_to_unmap(struct page *page, enum ttu_flags flags)
> int try_to_munlock(struct page *page)
> {
> int ret;
> + struct rmap_private rp = {
> + .flags = TTU_MUNLOCK,
> + };
> +
> struct rmap_walk_control rwc = {
> .rmap_one = try_to_unmap_one,
> - .arg = (void *)TTU_MUNLOCK,
> + .arg = &rp,
> .done = page_not_mapped,
> /*
> * We don't bother to try to find the munlocked page in
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index a9c74b409681..7f1c5a26bc41 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -684,6 +684,7 @@ enum page_references {
> PAGEREF_RECLAIM_CLEAN,
> PAGEREF_KEEP,
> PAGEREF_ACTIVATE,
> + PAGEREF_DISCARD,
> };
>
> static enum page_references page_check_references(struct page *page,
> @@ -691,9 +692,12 @@ static enum page_references page_check_references(struct page *page,
> {
> int referenced_ptes, referenced_page;
> unsigned long vm_flags;
> + int is_pte_dirty;
> +
> + VM_BUG_ON_PAGE(!PageLocked(page), page);
>
> referenced_ptes = page_referenced(page, 1, sc->target_mem_cgroup,
> - &vm_flags);
> + &vm_flags, &is_pte_dirty);
> referenced_page = TestClearPageReferenced(page);
>
> /*
> @@ -734,6 +738,18 @@ static enum page_references page_check_references(struct page *page,
> return PAGEREF_KEEP;
> }
>
> + /*
> + * We should check PageDirty because swap-in page by read fault
> + * will be swapcache and pte point out the page doesn't have
> + * dirty bit so only pte dirtiness check isn't enough. In this case,
> + * it would be good to check PG_swapcache to filter it out.
> + * If the page is removed from swapcache, it must have PG_dirty
> + * so we should check it to prevent purging non-lazyfree page.
> + */

Nice explanation. So this is the key point to know how to detect a lazyfree page,
I think something like this can be put in the patch log, too.

Thanks
Zhang

> + if (PageAnon(page) && !is_pte_dirty &&
> + !PageSwapCache(page) && !PageDirty(page))
> + return PAGEREF_DISCARD;
> +
> /* Reclaim if clean, defer dirty pages to writeback */
> if (referenced_page && !PageSwapBacked(page))
> return PAGEREF_RECLAIM_CLEAN;
> @@ -932,6 +948,8 @@ static unsigned long shrink_page_list(struct list_head *page_list,
> goto activate_locked;
> case PAGEREF_KEEP:
> goto keep_locked;
> + case PAGEREF_DISCARD:
> + goto discard;
> case PAGEREF_RECLAIM:
> case PAGEREF_RECLAIM_CLEAN:
> ; /* try to reclaim the page below */
> @@ -957,6 +975,7 @@ static unsigned long shrink_page_list(struct list_head *page_list,
> * processes. Try to unmap it here.
> */
> if (page_mapped(page) && mapping) {
> +discard:
> switch (try_to_unmap(page, ttu_flags)) {
> case SWAP_FAIL:
> goto activate_locked;
> @@ -964,6 +983,13 @@ static unsigned long shrink_page_list(struct list_head *page_list,
> goto keep_locked;
> case SWAP_MLOCK:
> goto cull_mlocked;
> + case SWAP_DISCARD:
> + 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;
> case SWAP_SUCCESS:
> ; /* try to free the page below */
> }
> @@ -1688,7 +1714,7 @@ 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 def5dd2fbe61..2d80f7ed495d 100644
> --- a/mm/vmstat.c
> +++ b/mm/vmstat.c
> @@ -789,6 +789,7 @@ const char * const vmstat_text[] = {
>
> "pgfault",
> "pgmajfault",
> + "pglazyfreed",
>
> TEXTS_FOR_ZONES("pgrefill")
> TEXTS_FOR_ZONES("pgsteal_kswapd")
>


--
Thanks.
Zhang Yanfei


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