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Message-ID: <5559B568.6060603@suse.cz>
Date: Mon, 18 May 2015 11:48:24 +0200
From: Vlastimil Babka <vbabka@...e.cz>
To: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Andrea Arcangeli <aarcange@...hat.com>,
Hugh Dickins <hughd@...gle.com>
CC: Dave Hansen <dave.hansen@...el.com>, Mel Gorman <mgorman@...e.de>,
Rik van Riel <riel@...hat.com>,
Christoph Lameter <cl@...two.org>,
Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
Steve Capper <steve.capper@...aro.org>,
"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
Johannes Weiner <hannes@...xchg.org>,
Michal Hocko <mhocko@...e.cz>,
Jerome Marchand <jmarchan@...hat.com>,
Sasha Levin <sasha.levin@...cle.com>,
linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCHv5 13/28] mm: drop tail page refcounting
On 04/23/2015 11:03 PM, Kirill A. Shutemov wrote:
> Tail page refcounting is utterly complicated and painful to support.
> It also make use of ->_mapcount to account pins on tail pages. We will
> need ->_mapcount acoount PTE mappings of subpages of the compound page.
>
> The only user of tail page refcounting is THP which is marked BROKEN for
> now.
>
> Let's drop all this mess. It makes get_page() and put_pag() much simplier.
Apart from several typos, this is another place where more details
wouldn't hurt.
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> Tested-by: Sasha Levin <sasha.levin@...cle.com>
Acked-by: Vlastimil Babka <vbabka@...e.cz>
> ---
> arch/mips/mm/gup.c | 4 -
> arch/powerpc/mm/hugetlbpage.c | 13 +-
> arch/s390/mm/gup.c | 13 +-
> arch/sparc/mm/gup.c | 14 +--
> arch/x86/mm/gup.c | 4 -
> include/linux/mm.h | 47 ++------
> include/linux/mm_types.h | 17 +--
> mm/gup.c | 34 +-----
> mm/huge_memory.c | 41 +------
> mm/hugetlb.c | 2 +-
> mm/internal.h | 44 -------
> mm/swap.c | 274 +++---------------------------------------
> 12 files changed, 40 insertions(+), 467 deletions(-)
>
> diff --git a/arch/mips/mm/gup.c b/arch/mips/mm/gup.c
> index 349995d19c7f..36a35115dc2e 100644
> --- a/arch/mips/mm/gup.c
> +++ b/arch/mips/mm/gup.c
> @@ -87,8 +87,6 @@ static int gup_huge_pmd(pmd_t pmd, unsigned long addr, unsigned long end,
> do {
> VM_BUG_ON(compound_head(page) != head);
> pages[*nr] = page;
> - if (PageTail(page))
> - get_huge_page_tail(page);
> (*nr)++;
> page++;
> refs++;
> @@ -153,8 +151,6 @@ static int gup_huge_pud(pud_t pud, unsigned long addr, unsigned long end,
> do {
> VM_BUG_ON(compound_head(page) != head);
> pages[*nr] = page;
> - if (PageTail(page))
> - get_huge_page_tail(page);
> (*nr)++;
> page++;
> refs++;
> diff --git a/arch/powerpc/mm/hugetlbpage.c b/arch/powerpc/mm/hugetlbpage.c
> index cf0464f4284f..f30ae0f7f570 100644
> --- a/arch/powerpc/mm/hugetlbpage.c
> +++ b/arch/powerpc/mm/hugetlbpage.c
> @@ -1037,7 +1037,7 @@ int gup_hugepte(pte_t *ptep, unsigned long sz, unsigned long addr,
> {
> unsigned long mask;
> unsigned long pte_end;
> - struct page *head, *page, *tail;
> + struct page *head, *page;
> pte_t pte;
> int refs;
>
> @@ -1060,7 +1060,6 @@ int gup_hugepte(pte_t *ptep, unsigned long sz, unsigned long addr,
> head = pte_page(pte);
>
> page = head + ((addr & (sz-1)) >> PAGE_SHIFT);
> - tail = page;
> do {
> VM_BUG_ON(compound_head(page) != head);
> pages[*nr] = page;
> @@ -1082,15 +1081,5 @@ int gup_hugepte(pte_t *ptep, unsigned long sz, unsigned long addr,
> return 0;
> }
>
> - /*
> - * Any tail page need their mapcount reference taken before we
> - * return.
> - */
> - while (refs--) {
> - if (PageTail(tail))
> - get_huge_page_tail(tail);
> - tail++;
> - }
> -
> return 1;
> }
> diff --git a/arch/s390/mm/gup.c b/arch/s390/mm/gup.c
> index 5c586c78ca8d..dab30527ad41 100644
> --- a/arch/s390/mm/gup.c
> +++ b/arch/s390/mm/gup.c
> @@ -52,7 +52,7 @@ static inline int gup_huge_pmd(pmd_t *pmdp, pmd_t pmd, unsigned long addr,
> unsigned long end, int write, struct page **pages, int *nr)
> {
> unsigned long mask, result;
> - struct page *head, *page, *tail;
> + struct page *head, *page;
> int refs;
>
> result = write ? 0 : _SEGMENT_ENTRY_PROTECT;
> @@ -64,7 +64,6 @@ static inline int gup_huge_pmd(pmd_t *pmdp, pmd_t pmd, unsigned long addr,
> refs = 0;
> head = pmd_page(pmd);
> page = head + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
> - tail = page;
> do {
> VM_BUG_ON(compound_head(page) != head);
> pages[*nr] = page;
> @@ -85,16 +84,6 @@ static inline int gup_huge_pmd(pmd_t *pmdp, pmd_t pmd, unsigned long addr,
> return 0;
> }
>
> - /*
> - * Any tail page need their mapcount reference taken before we
> - * return.
> - */
> - while (refs--) {
> - if (PageTail(tail))
> - get_huge_page_tail(tail);
> - tail++;
> - }
> -
> return 1;
> }
>
> diff --git a/arch/sparc/mm/gup.c b/arch/sparc/mm/gup.c
> index 2e5c4fc2daa9..9091c5daa2e1 100644
> --- a/arch/sparc/mm/gup.c
> +++ b/arch/sparc/mm/gup.c
> @@ -56,8 +56,6 @@ static noinline int gup_pte_range(pmd_t pmd, unsigned long addr,
> put_page(head);
> return 0;
> }
> - if (head != page)
> - get_huge_page_tail(page);
>
> pages[*nr] = page;
> (*nr)++;
> @@ -70,7 +68,7 @@ static int gup_huge_pmd(pmd_t *pmdp, pmd_t pmd, unsigned long addr,
> unsigned long end, int write, struct page **pages,
> int *nr)
> {
> - struct page *head, *page, *tail;
> + struct page *head, *page;
> int refs;
>
> if (!(pmd_val(pmd) & _PAGE_VALID))
> @@ -82,7 +80,6 @@ static int gup_huge_pmd(pmd_t *pmdp, pmd_t pmd, unsigned long addr,
> refs = 0;
> head = pmd_page(pmd);
> page = head + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
> - tail = page;
> do {
> VM_BUG_ON(compound_head(page) != head);
> pages[*nr] = page;
> @@ -103,15 +100,6 @@ static int gup_huge_pmd(pmd_t *pmdp, pmd_t pmd, unsigned long addr,
> return 0;
> }
>
> - /* Any tail page need their mapcount reference taken before we
> - * return.
> - */
> - while (refs--) {
> - if (PageTail(tail))
> - get_huge_page_tail(tail);
> - tail++;
> - }
> -
> return 1;
> }
>
> diff --git a/arch/x86/mm/gup.c b/arch/x86/mm/gup.c
> index 81bf3d2af3eb..62a887a3cf50 100644
> --- a/arch/x86/mm/gup.c
> +++ b/arch/x86/mm/gup.c
> @@ -137,8 +137,6 @@ static noinline int gup_huge_pmd(pmd_t pmd, unsigned long addr,
> do {
> VM_BUG_ON_PAGE(compound_head(page) != head, page);
> pages[*nr] = page;
> - if (PageTail(page))
> - get_huge_page_tail(page);
> (*nr)++;
> page++;
> refs++;
> @@ -214,8 +212,6 @@ static noinline int gup_huge_pud(pud_t pud, unsigned long addr,
> do {
> VM_BUG_ON_PAGE(compound_head(page) != head, page);
> pages[*nr] = page;
> - if (PageTail(page))
> - get_huge_page_tail(page);
> (*nr)++;
> page++;
> refs++;
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index efe8417360a2..dd1b5f2b1966 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -449,44 +449,9 @@ static inline int page_count(struct page *page)
> return atomic_read(&compound_head(page)->_count);
> }
>
> -static inline bool __compound_tail_refcounted(struct page *page)
> -{
> - return PageAnon(page) && !PageSlab(page) && !PageHeadHuge(page);
> -}
> -
> -/*
> - * This takes a head page as parameter and tells if the
> - * tail page reference counting can be skipped.
> - *
> - * For this to be safe, PageSlab and PageHeadHuge must remain true on
> - * any given page where they return true here, until all tail pins
> - * have been released.
> - */
> -static inline bool compound_tail_refcounted(struct page *page)
> -{
> - VM_BUG_ON_PAGE(!PageHead(page), page);
> - return __compound_tail_refcounted(page);
> -}
> -
> -static inline void get_huge_page_tail(struct page *page)
> -{
> - /*
> - * __split_huge_page_refcount() cannot run from under us.
> - */
> - VM_BUG_ON_PAGE(!PageTail(page), page);
> - VM_BUG_ON_PAGE(page_mapcount(page) < 0, page);
> - VM_BUG_ON_PAGE(atomic_read(&page->_count) != 0, page);
> - if (compound_tail_refcounted(page->first_page))
> - atomic_inc(&page->_mapcount);
> -}
> -
> -extern bool __get_page_tail(struct page *page);
> -
> static inline void get_page(struct page *page)
> {
> - if (unlikely(PageTail(page)))
> - if (likely(__get_page_tail(page)))
> - return;
> + page = compound_head(page);
> /*
> * Getting a normal page or the head of a compound page
> * requires to already have an elevated page->_count.
> @@ -517,7 +482,15 @@ static inline void init_page_count(struct page *page)
> atomic_set(&page->_count, 1);
> }
>
> -void put_page(struct page *page);
> +void __put_page(struct page* page);
> +
> +static inline void put_page(struct page *page)
> +{
> + page = compound_head(page);
> + if (put_page_testzero(page))
> + __put_page(page);
> +}
> +
> void put_pages_list(struct list_head *pages);
>
> void split_page(struct page *page, unsigned int order);
> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> index 590630eb59ba..126f481bb95a 100644
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -92,20 +92,9 @@ struct page {
>
> union {
> /*
> - * Count of ptes mapped in
> - * mms, to show when page is
> - * mapped & limit reverse map
> - * searches.
> - *
> - * Used also for tail pages
> - * refcounting instead of
> - * _count. Tail pages cannot
> - * be mapped and keeping the
> - * tail page _count zero at
> - * all times guarantees
> - * get_page_unless_zero() will
> - * never succeed on tail
> - * pages.
> + * Count of ptes mapped in mms, to show
> + * when page is mapped & limit reverse
> + * map searches.
> */
> atomic_t _mapcount;
>
> diff --git a/mm/gup.c b/mm/gup.c
> index 19e01f156abb..53f9681b7b30 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -93,7 +93,7 @@ retry:
> }
>
> if (flags & FOLL_GET)
> - get_page_foll(page);
> + get_page(page);
> if (flags & FOLL_TOUCH) {
> if ((flags & FOLL_WRITE) &&
> !pte_dirty(pte) && !PageDirty(page))
> @@ -1108,7 +1108,7 @@ static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end,
> static int gup_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
> unsigned long end, int write, struct page **pages, int *nr)
> {
> - struct page *head, *page, *tail;
> + struct page *head, *page;
> int refs;
>
> if (write && !pmd_write(orig))
> @@ -1117,7 +1117,6 @@ static int gup_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
> refs = 0;
> head = pmd_page(orig);
> page = head + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
> - tail = page;
> do {
> VM_BUG_ON_PAGE(compound_head(page) != head, page);
> pages[*nr] = page;
> @@ -1138,24 +1137,13 @@ static int gup_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
> return 0;
> }
>
> - /*
> - * Any tail pages need their mapcount reference taken before we
> - * return. (This allows the THP code to bump their ref count when
> - * they are split into base pages).
> - */
> - while (refs--) {
> - if (PageTail(tail))
> - get_huge_page_tail(tail);
> - tail++;
> - }
> -
> return 1;
> }
>
> static int gup_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr,
> unsigned long end, int write, struct page **pages, int *nr)
> {
> - struct page *head, *page, *tail;
> + struct page *head, *page;
> int refs;
>
> if (write && !pud_write(orig))
> @@ -1164,7 +1152,6 @@ static int gup_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr,
> refs = 0;
> head = pud_page(orig);
> page = head + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
> - tail = page;
> do {
> VM_BUG_ON_PAGE(compound_head(page) != head, page);
> pages[*nr] = page;
> @@ -1185,12 +1172,6 @@ static int gup_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr,
> return 0;
> }
>
> - while (refs--) {
> - if (PageTail(tail))
> - get_huge_page_tail(tail);
> - tail++;
> - }
> -
> return 1;
> }
>
> @@ -1199,7 +1180,7 @@ static int gup_huge_pgd(pgd_t orig, pgd_t *pgdp, unsigned long addr,
> struct page **pages, int *nr)
> {
> int refs;
> - struct page *head, *page, *tail;
> + struct page *head, *page;
>
> if (write && !pgd_write(orig))
> return 0;
> @@ -1207,7 +1188,6 @@ static int gup_huge_pgd(pgd_t orig, pgd_t *pgdp, unsigned long addr,
> refs = 0;
> head = pgd_page(orig);
> page = head + ((addr & ~PGDIR_MASK) >> PAGE_SHIFT);
> - tail = page;
> do {
> VM_BUG_ON_PAGE(compound_head(page) != head, page);
> pages[*nr] = page;
> @@ -1228,12 +1208,6 @@ static int gup_huge_pgd(pgd_t orig, pgd_t *pgdp, unsigned long addr,
> return 0;
> }
>
> - while (refs--) {
> - if (PageTail(tail))
> - get_huge_page_tail(tail);
> - tail++;
> - }
> -
> return 1;
> }
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index f3cc576dad73..16c6c262385c 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -941,37 +941,6 @@ unlock:
> spin_unlock(ptl);
> }
>
> -/*
> - * Save CONFIG_DEBUG_PAGEALLOC from faulting falsely on tail pages
> - * during copy_user_huge_page()'s copy_page_rep(): in the case when
> - * the source page gets split and a tail freed before copy completes.
> - * Called under pmd_lock of checked pmd, so safe from splitting itself.
> - */
> -static void get_user_huge_page(struct page *page)
> -{
> - if (IS_ENABLED(CONFIG_DEBUG_PAGEALLOC)) {
> - struct page *endpage = page + HPAGE_PMD_NR;
> -
> - atomic_add(HPAGE_PMD_NR, &page->_count);
> - while (++page < endpage)
> - get_huge_page_tail(page);
> - } else {
> - get_page(page);
> - }
> -}
> -
> -static void put_user_huge_page(struct page *page)
> -{
> - if (IS_ENABLED(CONFIG_DEBUG_PAGEALLOC)) {
> - struct page *endpage = page + HPAGE_PMD_NR;
> -
> - while (page < endpage)
> - put_page(page++);
> - } else {
> - put_page(page);
> - }
> -}
> -
> static int do_huge_pmd_wp_page_fallback(struct mm_struct *mm,
> struct vm_area_struct *vma,
> unsigned long address,
> @@ -1124,7 +1093,7 @@ int do_huge_pmd_wp_page(struct mm_struct *mm, struct vm_area_struct *vma,
> ret |= VM_FAULT_WRITE;
> goto out_unlock;
> }
> - get_user_huge_page(page);
> + get_page(page);
> spin_unlock(ptl);
> alloc:
> if (transparent_hugepage_enabled(vma) &&
> @@ -1145,7 +1114,7 @@ alloc:
> split_huge_pmd(vma, pmd, address);
> ret |= VM_FAULT_FALLBACK;
> }
> - put_user_huge_page(page);
> + put_page(page);
> }
> count_vm_event(THP_FAULT_FALLBACK);
> goto out;
> @@ -1156,7 +1125,7 @@ alloc:
> put_page(new_page);
> if (page) {
> split_huge_pmd(vma, pmd, address);
> - put_user_huge_page(page);
> + put_page(page);
> } else
> split_huge_pmd(vma, pmd, address);
> ret |= VM_FAULT_FALLBACK;
> @@ -1178,7 +1147,7 @@ alloc:
>
> spin_lock(ptl);
> if (page)
> - put_user_huge_page(page);
> + put_page(page);
> if (unlikely(!pmd_same(*pmd, orig_pmd))) {
> spin_unlock(ptl);
> mem_cgroup_cancel_charge(new_page, memcg, true);
> @@ -1263,7 +1232,7 @@ struct page *follow_trans_huge_pmd(struct vm_area_struct *vma,
> page += (addr & ~HPAGE_PMD_MASK) >> PAGE_SHIFT;
> VM_BUG_ON_PAGE(!PageCompound(page), page);
> if (flags & FOLL_GET)
> - get_page_foll(page);
> + get_page(page);
>
> out:
> return page;
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index eb2a0430535e..f27d4edada3a 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -3453,7 +3453,7 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
> same_page:
> if (pages) {
> pages[i] = mem_map_offset(page, pfn_offset);
> - get_page_foll(pages[i]);
> + get_page(pages[i]);
> }
>
> if (vmas)
> diff --git a/mm/internal.h b/mm/internal.h
> index a25e359a4039..98bce4d12a16 100644
> --- a/mm/internal.h
> +++ b/mm/internal.h
> @@ -47,50 +47,6 @@ static inline void set_page_refcounted(struct page *page)
> set_page_count(page, 1);
> }
>
> -static inline void __get_page_tail_foll(struct page *page,
> - bool get_page_head)
> -{
> - /*
> - * If we're getting a tail page, the elevated page->_count is
> - * required only in the head page and we will elevate the head
> - * page->_count and tail page->_mapcount.
> - *
> - * We elevate page_tail->_mapcount for tail pages to force
> - * page_tail->_count to be zero at all times to avoid getting
> - * false positives from get_page_unless_zero() with
> - * speculative page access (like in
> - * page_cache_get_speculative()) on tail pages.
> - */
> - VM_BUG_ON_PAGE(atomic_read(&page->first_page->_count) <= 0, page);
> - if (get_page_head)
> - atomic_inc(&page->first_page->_count);
> - get_huge_page_tail(page);
> -}
> -
> -/*
> - * This is meant to be called as the FOLL_GET operation of
> - * follow_page() and it must be called while holding the proper PT
> - * lock while the pte (or pmd_trans_huge) is still mapping the page.
> - */
> -static inline void get_page_foll(struct page *page)
> -{
> - if (unlikely(PageTail(page)))
> - /*
> - * This is safe only because
> - * __split_huge_page_refcount() can't run under
> - * get_page_foll() because we hold the proper PT lock.
> - */
> - __get_page_tail_foll(page, true);
> - else {
> - /*
> - * Getting a normal page or the head of a compound page
> - * requires to already have an elevated page->_count.
> - */
> - VM_BUG_ON_PAGE(atomic_read(&page->_count) <= 0, page);
> - atomic_inc(&page->_count);
> - }
> -}
> -
> extern unsigned long highest_memmap_pfn;
>
> /*
> diff --git a/mm/swap.c b/mm/swap.c
> index 8773de093171..39166c05e5f3 100644
> --- a/mm/swap.c
> +++ b/mm/swap.c
> @@ -89,261 +89,14 @@ static void __put_compound_page(struct page *page)
> (*dtor)(page);
> }
>
> -/**
> - * Two special cases here: we could avoid taking compound_lock_irqsave
> - * and could skip the tail refcounting(in _mapcount).
> - *
> - * 1. Hugetlbfs page:
> - *
> - * PageHeadHuge will remain true until the compound page
> - * is released and enters the buddy allocator, and it could
> - * not be split by __split_huge_page_refcount().
> - *
> - * So if we see PageHeadHuge set, and we have the tail page pin,
> - * then we could safely put head page.
> - *
> - * 2. Slab THP page:
> - *
> - * PG_slab is cleared before the slab frees the head page, and
> - * tail pin cannot be the last reference left on the head page,
> - * because the slab code is free to reuse the compound page
> - * after a kfree/kmem_cache_free without having to check if
> - * there's any tail pin left. In turn all tail pinsmust be always
> - * released while the head is still pinned by the slab code
> - * and so we know PG_slab will be still set too.
> - *
> - * So if we see PageSlab set, and we have the tail page pin,
> - * then we could safely put head page.
> - */
> -static __always_inline
> -void put_unrefcounted_compound_page(struct page *page_head, struct page *page)
> -{
> - /*
> - * If @page is a THP tail, we must read the tail page
> - * flags after the head page flags. The
> - * __split_huge_page_refcount side enforces write memory barriers
> - * between clearing PageTail and before the head page
> - * can be freed and reallocated.
> - */
> - smp_rmb();
> - if (likely(PageTail(page))) {
> - /*
> - * __split_huge_page_refcount cannot race
> - * here, see the comment above this function.
> - */
> - VM_BUG_ON_PAGE(!PageHead(page_head), page_head);
> - VM_BUG_ON_PAGE(page_mapcount(page) != 0, page);
> - if (put_page_testzero(page_head)) {
> - /*
> - * If this is the tail of a slab THP page,
> - * the tail pin must not be the last reference
> - * held on the page, because the PG_slab cannot
> - * be cleared before all tail pins (which skips
> - * the _mapcount tail refcounting) have been
> - * released.
> - *
> - * If this is the tail of a hugetlbfs page,
> - * the tail pin may be the last reference on
> - * the page instead, because PageHeadHuge will
> - * not go away until the compound page enters
> - * the buddy allocator.
> - */
> - VM_BUG_ON_PAGE(PageSlab(page_head), page_head);
> - __put_compound_page(page_head);
> - }
> - } else
> - /*
> - * __split_huge_page_refcount run before us,
> - * @page was a THP tail. The split @page_head
> - * has been freed and reallocated as slab or
> - * hugetlbfs page of smaller order (only
> - * possible if reallocated as slab on x86).
> - */
> - if (put_page_testzero(page))
> - __put_single_page(page);
> -}
> -
> -static __always_inline
> -void put_refcounted_compound_page(struct page *page_head, struct page *page)
> -{
> - if (likely(page != page_head && get_page_unless_zero(page_head))) {
> - unsigned long flags;
> -
> - /*
> - * @page_head wasn't a dangling pointer but it may not
> - * be a head page anymore by the time we obtain the
> - * lock. That is ok as long as it can't be freed from
> - * under us.
> - */
> - flags = compound_lock_irqsave(page_head);
> - if (unlikely(!PageTail(page))) {
> - /* __split_huge_page_refcount run before us */
> - compound_unlock_irqrestore(page_head, flags);
> - if (put_page_testzero(page_head)) {
> - /*
> - * The @page_head may have been freed
> - * and reallocated as a compound page
> - * of smaller order and then freed
> - * again. All we know is that it
> - * cannot have become: a THP page, a
> - * compound page of higher order, a
> - * tail page. That is because we
> - * still hold the refcount of the
> - * split THP tail and page_head was
> - * the THP head before the split.
> - */
> - if (PageHead(page_head))
> - __put_compound_page(page_head);
> - else
> - __put_single_page(page_head);
> - }
> -out_put_single:
> - if (put_page_testzero(page))
> - __put_single_page(page);
> - return;
> - }
> - VM_BUG_ON_PAGE(page_head != page->first_page, page);
> - /*
> - * We can release the refcount taken by
> - * get_page_unless_zero() now that
> - * __split_huge_page_refcount() is blocked on the
> - * compound_lock.
> - */
> - if (put_page_testzero(page_head))
> - VM_BUG_ON_PAGE(1, page_head);
> - /* __split_huge_page_refcount will wait now */
> - VM_BUG_ON_PAGE(page_mapcount(page) <= 0, page);
> - atomic_dec(&page->_mapcount);
> - VM_BUG_ON_PAGE(atomic_read(&page_head->_count) <= 0, page_head);
> - VM_BUG_ON_PAGE(atomic_read(&page->_count) != 0, page);
> - compound_unlock_irqrestore(page_head, flags);
> -
> - if (put_page_testzero(page_head)) {
> - if (PageHead(page_head))
> - __put_compound_page(page_head);
> - else
> - __put_single_page(page_head);
> - }
> - } else {
> - /* @page_head is a dangling pointer */
> - VM_BUG_ON_PAGE(PageTail(page), page);
> - goto out_put_single;
> - }
> -}
> -
> -static void put_compound_page(struct page *page)
> -{
> - struct page *page_head;
> -
> - /*
> - * We see the PageCompound set and PageTail not set, so @page maybe:
> - * 1. hugetlbfs head page, or
> - * 2. THP head page.
> - */
> - if (likely(!PageTail(page))) {
> - if (put_page_testzero(page)) {
> - /*
> - * By the time all refcounts have been released
> - * split_huge_page cannot run anymore from under us.
> - */
> - if (PageHead(page))
> - __put_compound_page(page);
> - else
> - __put_single_page(page);
> - }
> - return;
> - }
> -
> - /*
> - * We see the PageCompound set and PageTail set, so @page maybe:
> - * 1. a tail hugetlbfs page, or
> - * 2. a tail THP page, or
> - * 3. a split THP page.
> - *
> - * Case 3 is possible, as we may race with
> - * __split_huge_page_refcount tearing down a THP page.
> - */
> - page_head = compound_head_by_tail(page);
> - if (!__compound_tail_refcounted(page_head))
> - put_unrefcounted_compound_page(page_head, page);
> - else
> - put_refcounted_compound_page(page_head, page);
> -}
> -
> -void put_page(struct page *page)
> +void __put_page(struct page *page)
> {
> if (unlikely(PageCompound(page)))
> - put_compound_page(page);
> - else if (put_page_testzero(page))
> + __put_compound_page(page);
> + else
> __put_single_page(page);
> }
> -EXPORT_SYMBOL(put_page);
> -
> -/*
> - * This function is exported but must not be called by anything other
> - * than get_page(). It implements the slow path of get_page().
> - */
> -bool __get_page_tail(struct page *page)
> -{
> - /*
> - * This takes care of get_page() if run on a tail page
> - * returned by one of the get_user_pages/follow_page variants.
> - * get_user_pages/follow_page itself doesn't need the compound
> - * lock because it runs __get_page_tail_foll() under the
> - * proper PT lock that already serializes against
> - * split_huge_page().
> - */
> - unsigned long flags;
> - bool got;
> - struct page *page_head = compound_head(page);
> -
> - /* Ref to put_compound_page() comment. */
> - if (!__compound_tail_refcounted(page_head)) {
> - smp_rmb();
> - if (likely(PageTail(page))) {
> - /*
> - * This is a hugetlbfs page or a slab
> - * page. __split_huge_page_refcount
> - * cannot race here.
> - */
> - VM_BUG_ON_PAGE(!PageHead(page_head), page_head);
> - __get_page_tail_foll(page, true);
> - return true;
> - } else {
> - /*
> - * __split_huge_page_refcount run
> - * before us, "page" was a THP
> - * tail. The split page_head has been
> - * freed and reallocated as slab or
> - * hugetlbfs page of smaller order
> - * (only possible if reallocated as
> - * slab on x86).
> - */
> - return false;
> - }
> - }
> -
> - got = false;
> - if (likely(page != page_head && get_page_unless_zero(page_head))) {
> - /*
> - * page_head wasn't a dangling pointer but it
> - * may not be a head page anymore by the time
> - * we obtain the lock. That is ok as long as it
> - * can't be freed from under us.
> - */
> - flags = compound_lock_irqsave(page_head);
> - /* here __split_huge_page_refcount won't run anymore */
> - if (likely(PageTail(page))) {
> - __get_page_tail_foll(page, false);
> - got = true;
> - }
> - compound_unlock_irqrestore(page_head, flags);
> - if (unlikely(!got))
> - put_page(page_head);
> - }
> - return got;
> -}
> -EXPORT_SYMBOL(__get_page_tail);
> +EXPORT_SYMBOL(__put_page);
>
> /**
> * put_pages_list() - release a list of pages
> @@ -960,15 +713,6 @@ void release_pages(struct page **pages, int nr, bool cold)
> for (i = 0; i < nr; i++) {
> struct page *page = pages[i];
>
> - if (unlikely(PageCompound(page))) {
> - if (zone) {
> - spin_unlock_irqrestore(&zone->lru_lock, flags);
> - zone = NULL;
> - }
> - put_compound_page(page);
> - continue;
> - }
> -
> /*
> * Make sure the IRQ-safe lock-holding time does not get
> * excessive with a continuous string of pages from the
> @@ -979,9 +723,19 @@ void release_pages(struct page **pages, int nr, bool cold)
> zone = NULL;
> }
>
> + page = compound_head(page);
> if (!put_page_testzero(page))
> continue;
>
> + if (PageCompound(page)) {
> + if (zone) {
> + spin_unlock_irqrestore(&zone->lru_lock, flags);
> + zone = NULL;
> + }
> + __put_compound_page(page);
> + continue;
> + }
> +
> if (PageLRU(page)) {
> struct zone *pagezone = page_zone(page);
>
>
--
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