mm: ZERO_PAGE without PTE_SPECIAL
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@tiscali.co.uk>
Cc: Rik van Riel <riel@redhat.com>
Reviewed-by: 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>
Cc: Ralf Baechle <ralf@linux-mips.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/memory.c b/mm/memory.c
index 5c694f2..9bdbd10 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -108,7 +108,7 @@
}
__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 @@
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 @@
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 @@
}
}
+ 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 @@
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);
}
@@ -1443,10 +1459,6 @@
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;
}
@@ -1629,7 +1641,8 @@
* 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;
@@ -2097,7 +2110,7 @@
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;
@@ -2658,8 +2671,9 @@
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))