Reinstate anonymous use of ZERO_PAGE to all architectures, not just to those which __HAVE_ARCH_PTE_SPECIAL: as suggested by Nick Piggin. Contrary to how I'd imagined it, there's nothing ugly about this, just a zero_pfn test built into one or another block of vm_normal_page(). But the MIPS ZERO_PAGE-of-many-colours case demands is_zero_pfn() and my_zero_pfn() inlines. Reinstate its mremap move_pte() shuffling of ZERO_PAGEs we did from 2.6.17 to 2.6.19? Not unless someone shouts for that: it would have to take vm_flags to weed out some cases. Signed-off-by: Hugh Dickins <hugh.dickins@xxxxxxxxxxxxx> --- I've not built and tested the actual MIPS case, just hacked up x86 definitions to simulate it; had to drop the static from zero_pfn. arch/mips/include/asm/pgtable.h | 14 +++++++++++ mm/memory.c | 36 ++++++++++++++++++++---------- 2 files changed, 39 insertions(+), 11 deletions(-) --- mm2/arch/mips/include/asm/pgtable.h 2009-09-09 23:13:59.000000000 +0100 +++ mm3/arch/mips/include/asm/pgtable.h 2009-09-15 17:32:19.000000000 +0100 @@ -76,6 +76,20 @@ extern unsigned long zero_page_mask; #define ZERO_PAGE(vaddr) \ (virt_to_page((void *)(empty_zero_page + (((unsigned long)(vaddr)) & zero_page_mask)))) +#define is_zero_pfn is_zero_pfn +static inline int is_zero_pfn(unsigned long pfn) +{ + extern unsigned long zero_pfn; + unsigned long offset_from_zero_pfn = pfn - zero_pfn; + return offset_from_zero_pfn <= (zero_page_mask >> PAGE_SHIFT); +} + +#define my_zero_pfn my_zero_pfn +static inline unsigned long my_zero_pfn(unsigned long addr) +{ + return page_to_pfn(ZERO_PAGE(addr)); +} + extern void paging_init(void); /* --- mm2/mm/memory.c 2009-09-14 16:34:37.000000000 +0100 +++ mm3/mm/memory.c 2009-09-15 17:32:19.000000000 +0100 @@ -107,7 +107,7 @@ static int __init disable_randmaps(char } __setup("norandmaps", disable_randmaps); -static unsigned long zero_pfn __read_mostly; +unsigned long zero_pfn __read_mostly; /* * CONFIG_MMU architectures set up ZERO_PAGE in their paging_init() @@ -455,6 +455,20 @@ static inline int is_cow_mapping(unsigne return (flags & (VM_SHARED | VM_MAYWRITE)) == VM_MAYWRITE; } +#ifndef is_zero_pfn +static inline int is_zero_pfn(unsigned long pfn) +{ + return pfn == zero_pfn; +} +#endif + +#ifndef my_zero_pfn +static inline unsigned long my_zero_pfn(unsigned long addr) +{ + return zero_pfn; +} +#endif + /* * vm_normal_page -- This function gets the "struct page" associated with a pte. * @@ -512,7 +526,7 @@ struct page *vm_normal_page(struct vm_ar goto check_pfn; if (vma->vm_flags & (VM_PFNMAP | VM_MIXEDMAP)) return NULL; - if (pfn != zero_pfn) + if (!is_zero_pfn(pfn)) print_bad_pte(vma, addr, pte, NULL); return NULL; } @@ -534,6 +548,8 @@ struct page *vm_normal_page(struct vm_ar } } + if (is_zero_pfn(pfn)) + return NULL; check_pfn: if (unlikely(pfn > highest_memmap_pfn)) { print_bad_pte(vma, addr, pte, NULL); @@ -1161,7 +1177,7 @@ struct page *follow_page(struct vm_area_ page = vm_normal_page(vma, address, pte); if (unlikely(!page)) { if ((flags & FOLL_DUMP) || - pte_pfn(pte) != zero_pfn) + !is_zero_pfn(pte_pfn(pte))) goto bad_page; page = pte_page(pte); } @@ -1444,10 +1460,6 @@ struct page *get_dump_page(unsigned long if (__get_user_pages(current, current->mm, addr, 1, FOLL_FORCE | FOLL_DUMP | FOLL_GET, &page, &vma) < 1) return NULL; - if (page == ZERO_PAGE(0)) { - page_cache_release(page); - return NULL; - } flush_cache_page(vma, addr, page_to_pfn(page)); return page; } @@ -1630,7 +1642,8 @@ int vm_insert_mixed(struct vm_area_struc * If we don't have pte special, then we have to use the pfn_valid() * based VM_MIXEDMAP scheme (see vm_normal_page), and thus we *must* * refcount the page if pfn_valid is true (hence insert_page rather - * than insert_pfn). + * than insert_pfn). If a zero_pfn were inserted into a VM_MIXEDMAP + * without pte special, it would there be refcounted as a normal page. */ if (!HAVE_PTE_SPECIAL && pfn_valid(pfn)) { struct page *page; @@ -2098,7 +2111,7 @@ gotten: if (unlikely(anon_vma_prepare(vma))) goto oom; - if (pte_pfn(orig_pte) == zero_pfn) { + if (is_zero_pfn(pte_pfn(orig_pte))) { new_page = alloc_zeroed_user_highpage_movable(vma, address); if (!new_page) goto oom; @@ -2613,8 +2626,9 @@ static int do_anonymous_page(struct mm_s spinlock_t *ptl; pte_t entry; - if (HAVE_PTE_SPECIAL && !(flags & FAULT_FLAG_WRITE)) { - entry = pte_mkspecial(pfn_pte(zero_pfn, vma->vm_page_prot)); + if (!(flags & FAULT_FLAG_WRITE)) { + entry = pte_mkspecial(pfn_pte(my_zero_pfn(address), + vma->vm_page_prot)); ptl = pte_lockptr(mm, pmd); spin_lock(ptl); if (!pte_none(*page_table)) -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html