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authorHugh Dickins <hugh.dickins@tiscali.co.uk>2009-09-21 17:03:30 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2009-09-22 07:17:40 -0700
commita13ea5b759645a0779edc6dbfec9abfd83220844 (patch)
tree864dd495718195bd065d9f26edac2504e6de5af0
parent1ac0cb5d0e22d5e483f56b2bc12172dec1cf7536 (diff)
mm: reinstate ZERO_PAGE
KAMEZAWA Hiroyuki has observed customers of earlier kernels taking advantage of the ZERO_PAGE: which we stopped do_anonymous_page() from using in 2.6.24. And there were a couple of regression reports on LKML. Following suggestions from Linus, reinstate do_anonymous_page() use of the ZERO_PAGE; but this time avoid dirtying its struct page cacheline with (map)count updates - let vm_normal_page() regard it as abnormal. Use it only on arches which __HAVE_ARCH_PTE_SPECIAL (x86, s390, sh32, most powerpc): that's not essential, but minimizes additional branches (keeping them in the unlikely pte_special case); and incidentally excludes mips (some models of which needed eight colours of ZERO_PAGE to avoid costly exceptions). Don't be fanatical about avoiding ZERO_PAGE updates: get_user_pages() callers won't want to make exceptions for it, so increment its count there. Changes to mlock and migration? happily seems not needed. In most places it's quicker to check pfn than struct page address: prepare a __read_mostly zero_pfn for that. Does get_dump_page() still need its ZERO_PAGE check? probably not, but keep it anyway. Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk> Acked-by: Rik van Riel <riel@redhat.com> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Cc: Nick Piggin <npiggin@suse.de> Cc: Mel Gorman <mel@csn.ul.ie> Cc: Minchan Kim <minchan.kim@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--mm/memory.c53
1 files changed, 44 insertions, 9 deletions
diff --git a/mm/memory.c b/mm/memory.c
index fc38d4ed9ad..c8b5b9435a9 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -108,6 +108,17 @@ static int __init disable_randmaps(char *s)
}
__setup("norandmaps", disable_randmaps);
+static unsigned long zero_pfn __read_mostly;
+
+/*
+ * CONFIG_MMU architectures set up ZERO_PAGE in their paging_init()
+ */
+static int __init init_zero_pfn(void)
+{
+ zero_pfn = page_to_pfn(ZERO_PAGE(0));
+ return 0;
+}
+core_initcall(init_zero_pfn);
/*
* If a p?d_bad entry is found while walking page tables, report
@@ -499,7 +510,9 @@ struct page *vm_normal_page(struct vm_area_struct *vma, unsigned long addr,
if (HAVE_PTE_SPECIAL) {
if (likely(!pte_special(pte)))
goto check_pfn;
- if (!(vma->vm_flags & (VM_PFNMAP | VM_MIXEDMAP)))
+ if (vma->vm_flags & (VM_PFNMAP | VM_MIXEDMAP))
+ return NULL;
+ if (pfn != zero_pfn)
print_bad_pte(vma, addr, pte, NULL);
return NULL;
}
@@ -1144,9 +1157,14 @@ struct page *follow_page(struct vm_area_struct *vma, unsigned long address,
goto no_page;
if ((flags & FOLL_WRITE) && !pte_write(pte))
goto unlock;
+
page = vm_normal_page(vma, address, pte);
- if (unlikely(!page))
- goto bad_page;
+ if (unlikely(!page)) {
+ if ((flags & FOLL_DUMP) ||
+ pte_pfn(pte) != zero_pfn)
+ goto bad_page;
+ page = pte_page(pte);
+ }
if (flags & FOLL_GET)
get_page(page);
@@ -2084,10 +2102,19 @@ gotten:
if (unlikely(anon_vma_prepare(vma)))
goto oom;
- VM_BUG_ON(old_page == ZERO_PAGE(0));
- new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, address);
- if (!new_page)
- goto oom;
+
+ if (pte_pfn(orig_pte) == zero_pfn) {
+ new_page = alloc_zeroed_user_highpage_movable(vma, address);
+ if (!new_page)
+ goto oom;
+ } else {
+ new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, address);
+ if (!new_page)
+ goto oom;
+ cow_user_page(new_page, old_page, address, vma);
+ }
+ __SetPageUptodate(new_page);
+
/*
* Don't let another task, with possibly unlocked vma,
* keep the mlocked page.
@@ -2097,8 +2124,6 @@ gotten:
clear_page_mlock(old_page);
unlock_page(old_page);
}
- cow_user_page(new_page, old_page, address, vma);
- __SetPageUptodate(new_page);
if (mem_cgroup_newpage_charge(new_page, mm, GFP_KERNEL))
goto oom_free_new;
@@ -2639,6 +2664,15 @@ static int do_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma,
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));
+ ptl = pte_lockptr(mm, pmd);
+ spin_lock(ptl);
+ if (!pte_none(*page_table))
+ goto unlock;
+ goto setpte;
+ }
+
/* Allocate our own private page. */
pte_unmap(page_table);
@@ -2662,6 +2696,7 @@ static int do_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma,
inc_mm_counter(mm, anon_rss);
page_add_new_anon_rmap(page, vma, address);
+setpte:
set_pte_at(mm, address, page_table, entry);
/* No need to invalidate - it was non-present before */