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SubjectRe: [PATCHv4 00/24] THP refcounting redesign
On 03/06/2015 01:18 PM, Kirill A. Shutemov wrote:
> On Thu, Mar 05, 2015 at 01:55:15PM +0100, Jerome Marchand wrote:
>> On 03/04/2015 05:32 PM, Kirill A. Shutemov wrote:
>>> Hello everybody,
>>>
>>> It's bug-fix update of my thp refcounting work.
>>>
>>> The goal of patchset is to make refcounting on THP pages cheaper with
>>> simpler semantics and allow the same THP compound page to be mapped with
>>> PMD and PTEs. This is required to get reasonable THP-pagecache
>>> implementation.
>>>
>>> With the new refcounting design it's much easier to protect against
>>> split_huge_page(): simple reference on a page will make you the deal.
>>> It makes gup_fast() implementation simpler and doesn't require
>>> special-case in futex code to handle tail THP pages.
>>>
>>> It should improve THP utilization over the system since splitting THP in
>>> one process doesn't necessary lead to splitting the page in all other
>>> processes have the page mapped.
>>>
>> [...]
>>> I believe all known bugs have been fixed, but I'm sure Sasha will bring more
>>> reports.
>>>
>>> The patchset also available on git:
>>>
>>> git://git.kernel.org/pub/scm/linux/kernel/git/kas/linux.git thp/refcounting/v4
>>>
>>
>> Hi Kirill,
>>
>> I ran some ltp tests and it triggered two bugs:
>>
>
> Could you test with the patch below?

It seems to fix the issue. I can't reproduce the bugs anymore.

Thanks,
Jerome

>
> diff --git a/arch/arc/mm/cache_arc700.c b/arch/arc/mm/cache_arc700.c
> index 8c3a3e02ba92..1baa4d23314b 100644
> --- a/arch/arc/mm/cache_arc700.c
> +++ b/arch/arc/mm/cache_arc700.c
> @@ -490,7 +490,7 @@ void flush_dcache_page(struct page *page)
> */
> if (!mapping_mapped(mapping)) {
> clear_bit(PG_dc_clean, &page->flags);
> - } else if (page_mapped(page)) {
> + } else if (page_mapcount(page)) {
>
> /* kernel reading from page with U-mapping */
> void *paddr = page_address(page);
> @@ -675,7 +675,7 @@ void copy_user_highpage(struct page *to, struct page *from,
> * Note that while @u_vaddr refers to DST page's userspace vaddr, it is
> * equally valid for SRC page as well
> */
> - if (page_mapped(from) && addr_not_cache_congruent(kfrom, u_vaddr)) {
> + if (page_mapcount(from) && addr_not_cache_congruent(kfrom, u_vaddr)) {
> __flush_dcache_page(kfrom, u_vaddr);
> clean_src_k_mappings = 1;
> }
> diff --git a/arch/arm/mm/flush.c b/arch/arm/mm/flush.c
> index 34b66af516ea..8f972fc8933d 100644
> --- a/arch/arm/mm/flush.c
> +++ b/arch/arm/mm/flush.c
> @@ -315,7 +315,7 @@ void flush_dcache_page(struct page *page)
> mapping = page_mapping(page);
>
> if (!cache_ops_need_broadcast() &&
> - mapping && !page_mapped(page))
> + mapping && !page_mapcount(page))
> clear_bit(PG_dcache_clean, &page->flags);
> else {
> __flush_dcache_page(mapping, page);
> diff --git a/arch/mips/mm/c-r4k.c b/arch/mips/mm/c-r4k.c
> index 3f8059602765..b28bf185ef77 100644
> --- a/arch/mips/mm/c-r4k.c
> +++ b/arch/mips/mm/c-r4k.c
> @@ -578,7 +578,8 @@ static inline void local_r4k_flush_cache_page(void *args)
> * another ASID than the current one.
> */
> map_coherent = (cpu_has_dc_aliases &&
> - page_mapped(page) && !Page_dcache_dirty(page));
> + page_mapcount(page) &&
> + !Page_dcache_dirty(page));
> if (map_coherent)
> vaddr = kmap_coherent(page, addr);
> else
> diff --git a/arch/mips/mm/cache.c b/arch/mips/mm/cache.c
> index 7e3ea7766822..e695b28dc32c 100644
> --- a/arch/mips/mm/cache.c
> +++ b/arch/mips/mm/cache.c
> @@ -106,7 +106,7 @@ void __flush_anon_page(struct page *page, unsigned long vmaddr)
> unsigned long addr = (unsigned long) page_address(page);
>
> if (pages_do_alias(addr, vmaddr)) {
> - if (page_mapped(page) && !Page_dcache_dirty(page)) {
> + if (page_mapcount(page) && !Page_dcache_dirty(page)) {
> void *kaddr;
>
> kaddr = kmap_coherent(page, vmaddr);
> diff --git a/arch/mips/mm/init.c b/arch/mips/mm/init.c
> index 448cde372af0..2c8e44aa536e 100644
> --- a/arch/mips/mm/init.c
> +++ b/arch/mips/mm/init.c
> @@ -156,7 +156,7 @@ void copy_user_highpage(struct page *to, struct page *from,
>
> vto = kmap_atomic(to);
> if (cpu_has_dc_aliases &&
> - page_mapped(from) && !Page_dcache_dirty(from)) {
> + page_mapcount(from) && !Page_dcache_dirty(from)) {
> vfrom = kmap_coherent(from, vaddr);
> copy_page(vto, vfrom);
> kunmap_coherent();
> @@ -178,7 +178,7 @@ void copy_to_user_page(struct vm_area_struct *vma,
> unsigned long len)
> {
> if (cpu_has_dc_aliases &&
> - page_mapped(page) && !Page_dcache_dirty(page)) {
> + page_mapcount(page) && !Page_dcache_dirty(page)) {
> void *vto = kmap_coherent(page, vaddr) + (vaddr & ~PAGE_MASK);
> memcpy(vto, src, len);
> kunmap_coherent();
> @@ -196,7 +196,7 @@ void copy_from_user_page(struct vm_area_struct *vma,
> unsigned long len)
> {
> if (cpu_has_dc_aliases &&
> - page_mapped(page) && !Page_dcache_dirty(page)) {
> + page_mapcount(page) && !Page_dcache_dirty(page)) {
> void *vfrom = kmap_coherent(page, vaddr) + (vaddr & ~PAGE_MASK);
> memcpy(dst, vfrom, len);
> kunmap_coherent();
> diff --git a/arch/sh/mm/cache-sh4.c b/arch/sh/mm/cache-sh4.c
> index 51d8f7f31d1d..58aaa4f33b81 100644
> --- a/arch/sh/mm/cache-sh4.c
> +++ b/arch/sh/mm/cache-sh4.c
> @@ -241,7 +241,7 @@ static void sh4_flush_cache_page(void *args)
> */
> map_coherent = (current_cpu_data.dcache.n_aliases &&
> test_bit(PG_dcache_clean, &page->flags) &&
> - page_mapped(page));
> + page_mapcount(page));
> if (map_coherent)
> vaddr = kmap_coherent(page, address);
> else
> diff --git a/arch/sh/mm/cache.c b/arch/sh/mm/cache.c
> index f770e3992620..e58cfbf45150 100644
> --- a/arch/sh/mm/cache.c
> +++ b/arch/sh/mm/cache.c
> @@ -59,7 +59,7 @@ void copy_to_user_page(struct vm_area_struct *vma, struct page *page,
> unsigned long vaddr, void *dst, const void *src,
> unsigned long len)
> {
> - if (boot_cpu_data.dcache.n_aliases && page_mapped(page) &&
> + if (boot_cpu_data.dcache.n_aliases && page_mapcount(page) &&
> test_bit(PG_dcache_clean, &page->flags)) {
> void *vto = kmap_coherent(page, vaddr) + (vaddr & ~PAGE_MASK);
> memcpy(vto, src, len);
> @@ -78,7 +78,7 @@ void copy_from_user_page(struct vm_area_struct *vma, struct page *page,
> unsigned long vaddr, void *dst, const void *src,
> unsigned long len)
> {
> - if (boot_cpu_data.dcache.n_aliases && page_mapped(page) &&
> + if (boot_cpu_data.dcache.n_aliases && page_mapcount(page) &&
> test_bit(PG_dcache_clean, &page->flags)) {
> void *vfrom = kmap_coherent(page, vaddr) + (vaddr & ~PAGE_MASK);
> memcpy(dst, vfrom, len);
> @@ -97,7 +97,7 @@ void copy_user_highpage(struct page *to, struct page *from,
>
> vto = kmap_atomic(to);
>
> - if (boot_cpu_data.dcache.n_aliases && page_mapped(from) &&
> + if (boot_cpu_data.dcache.n_aliases && page_mapcount(from) &&
> test_bit(PG_dcache_clean, &from->flags)) {
> vfrom = kmap_coherent(from, vaddr);
> copy_page(vto, vfrom);
> @@ -153,7 +153,7 @@ void __flush_anon_page(struct page *page, unsigned long vmaddr)
> unsigned long addr = (unsigned long) page_address(page);
>
> if (pages_do_alias(addr, vmaddr)) {
> - if (boot_cpu_data.dcache.n_aliases && page_mapped(page) &&
> + if (boot_cpu_data.dcache.n_aliases && page_mapcount(page) &&
> test_bit(PG_dcache_clean, &page->flags)) {
> void *kaddr;
>
> diff --git a/arch/xtensa/mm/tlb.c b/arch/xtensa/mm/tlb.c
> index 5ece856c5725..35c822286bbe 100644
> --- a/arch/xtensa/mm/tlb.c
> +++ b/arch/xtensa/mm/tlb.c
> @@ -245,7 +245,7 @@ static int check_tlb_entry(unsigned w, unsigned e, bool dtlb)
> page_mapcount(p));
> if (!page_count(p))
> rc |= TLB_INSANE;
> - else if (page_mapped(p))
> + else if (page_mapcount(p))
> rc |= TLB_SUSPICIOUS;
> } else {
> rc |= TLB_INSANE;
> diff --git a/fs/proc/page.c b/fs/proc/page.c
> index 7eee2d8b97d9..e99c059339f6 100644
> --- a/fs/proc/page.c
> +++ b/fs/proc/page.c
> @@ -97,9 +97,9 @@ u64 stable_page_flags(struct page *page)
> * pseudo flags for the well known (anonymous) memory mapped pages
> *
> * Note that page->_mapcount is overloaded in SLOB/SLUB/SLQB, so the
> - * simple test in page_mapped() is not enough.
> + * simple test in page_mapcount() is not enough.
> */
> - if (!PageSlab(page) && page_mapped(page))
> + if (!PageSlab(page) && page_mapcount(page))
> u |= 1 << KPF_MMAP;
> if (PageAnon(page))
> u |= 1 << KPF_ANON;
> diff --git a/mm/filemap.c b/mm/filemap.c
> index 25bec2c3e7a3..da8f66067670 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -200,7 +200,7 @@ void __delete_from_page_cache(struct page *page, void *shadow)
> __dec_zone_page_state(page, NR_FILE_PAGES);
> if (PageSwapBacked(page))
> __dec_zone_page_state(page, NR_SHMEM);
> - BUG_ON(page_mapped(page));
> + VM_BUG_ON_PAGE(page_mapped(page), page);
>
> /*
> * At this point page must be either written or cleaned by truncate.
> diff --git a/mm/rmap.c b/mm/rmap.c
> index 7b8838f2c5d0..3361fe78fbe2 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -1141,12 +1141,15 @@ static void page_remove_file_rmap(struct page *page)
>
> memcg = mem_cgroup_begin_page_stat(page);
>
> - /* page still mapped by someone else? */
> - if (!atomic_add_negative(-1, &page->_mapcount))
> + /* Hugepages are not counted in NR_FILE_MAPPED for now. */
> + if (unlikely(PageHuge(page))) {
> + /* hugetlb pages are always mapped with pmds */
> + atomic_dec(compound_mapcount_ptr(page));
> goto out;
> + }
>
> - /* Hugepages are not counted in NR_FILE_MAPPED for now. */
> - if (unlikely(PageHuge(page)))
> + /* page still mapped by someone else? */
> + if (!atomic_add_negative(-1, &page->_mapcount))
> goto out;
>
> /*
>


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