[PATCH] mm: split highorder pages
Have an explicit mm call to split higher order pages into individual pages.
Should help to avoid bugs and be more explicit about the code's intention.
Signed-off-by: Nick Piggin <npiggin@suse.de>
Cc: Russell King <rmk@arm.linux.org.uk>
Cc: David Howells <dhowells@redhat.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mundt <lethal@linux-sh.org>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Chris Zankel <chris@zankel.net>
Signed-off-by: Yoichi Yuasa <yoichi_yuasa@tripeaks.co.jp>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/arch/arm/mm/consistent.c b/arch/arm/mm/consistent.c
index c2ee18d..8a1bfcd 100644
--- a/arch/arm/mm/consistent.c
+++ b/arch/arm/mm/consistent.c
@@ -223,6 +223,8 @@
pte = consistent_pte[idx] + off;
c->vm_pages = page;
+ split_page(page, order);
+
/*
* Set the "dma handle"
*/
@@ -231,7 +233,6 @@
do {
BUG_ON(!pte_none(*pte));
- set_page_count(page, 1);
/*
* x86 does not mark the pages reserved...
*/
@@ -250,7 +251,6 @@
* Free the otherwise unused pages.
*/
while (page < end) {
- set_page_count(page, 1);
__free_page(page);
page++;
}
diff --git a/arch/frv/mm/dma-alloc.c b/arch/frv/mm/dma-alloc.c
index 342823a..636b2f8 100644
--- a/arch/frv/mm/dma-alloc.c
+++ b/arch/frv/mm/dma-alloc.c
@@ -115,9 +115,7 @@
*/
if (order > 0) {
struct page *rpage = virt_to_page(page);
-
- for (i = 1; i < (1 << order); i++)
- set_page_count(rpage + i, 1);
+ split_page(rpage, order);
}
err = 0;
diff --git a/arch/mips/mm/init.c b/arch/mips/mm/init.c
index 0ff9a34..a140da9 100644
--- a/arch/mips/mm/init.c
+++ b/arch/mips/mm/init.c
@@ -54,7 +54,8 @@
*/
unsigned long setup_zero_pages(void)
{
- unsigned long order, size;
+ unsigned int order;
+ unsigned long size;
struct page *page;
if (cpu_has_vce)
@@ -67,9 +68,9 @@
panic("Oh boy, that early out of memory?");
page = virt_to_page(empty_zero_page);
+ split_page(page, order);
while (page < virt_to_page(empty_zero_page + (PAGE_SIZE << order))) {
SetPageReserved(page);
- set_page_count(page, 1);
page++;
}
diff --git a/arch/ppc/kernel/dma-mapping.c b/arch/ppc/kernel/dma-mapping.c
index 685fd0d..61465ec 100644
--- a/arch/ppc/kernel/dma-mapping.c
+++ b/arch/ppc/kernel/dma-mapping.c
@@ -223,6 +223,8 @@
pte_t *pte = consistent_pte + CONSISTENT_OFFSET(vaddr);
struct page *end = page + (1 << order);
+ split_page(page, order);
+
/*
* Set the "dma handle"
*/
@@ -231,7 +233,6 @@
do {
BUG_ON(!pte_none(*pte));
- set_page_count(page, 1);
SetPageReserved(page);
set_pte_at(&init_mm, vaddr,
pte, mk_pte(page, pgprot_noncached(PAGE_KERNEL)));
@@ -244,7 +245,6 @@
* Free the otherwise unused pages.
*/
while (page < end) {
- set_page_count(page, 1);
__free_page(page);
page++;
}
diff --git a/arch/sh/mm/consistent.c b/arch/sh/mm/consistent.c
index df3a9e4..ee73e30 100644
--- a/arch/sh/mm/consistent.c
+++ b/arch/sh/mm/consistent.c
@@ -23,6 +23,7 @@
page = alloc_pages(gfp, order);
if (!page)
return NULL;
+ split_page(page, order);
ret = page_address(page);
*handle = virt_to_phys(ret);
@@ -37,8 +38,6 @@
end = page + (1 << order);
while (++page < end) {
- set_page_count(page, 1);
-
/* Free any unused pages */
if (page >= free) {
__free_page(page);
diff --git a/arch/xtensa/mm/pgtable.c b/arch/xtensa/mm/pgtable.c
index cbc56ae..7d28914 100644
--- a/arch/xtensa/mm/pgtable.c
+++ b/arch/xtensa/mm/pgtable.c
@@ -21,13 +21,9 @@
p = (pte_t*) __get_free_pages(GFP_KERNEL|__GFP_REPEAT, COLOR_ORDER);
if (likely(p)) {
- struct page *page;
+ split_page(virt_to_page(p), COLOR_ORDER);
for (i = 0; i < COLOR_SIZE; i++) {
- page = virt_to_page(p);
-
- set_page_count(page, 1);
-
if (ADDR_COLOR(p) == color)
pte = p;
else
@@ -55,9 +51,9 @@
p = alloc_pages(GFP_KERNEL | __GFP_REPEAT, PTE_ORDER);
if (likely(p)) {
- for (i = 0; i < PAGE_ORDER; i++) {
- set_page_count(p, 1);
+ split_page(p, COLOR_ORDER);
+ for (i = 0; i < PAGE_ORDER; i++) {
if (PADDR_COLOR(page_address(p)) == color)
page = p;
else
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 9bbddf2..e679806 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -328,6 +328,12 @@
void put_page(struct page *page);
+#ifdef CONFIG_MMU
+void split_page(struct page *page, unsigned int order);
+#else
+static inline void split_page(struct page *page, unsigned int order) {}
+#endif
+
/*
* Multiple processes may "see" the same page. E.g. for untouched
* mappings of /dev/null, all processes see the same page full of
diff --git a/mm/memory.c b/mm/memory.c
index 85e80a5..6af555c 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1221,9 +1221,7 @@
* The page has to be a nice clean _individual_ kernel allocation.
* If you allocate a compound page, you need to have marked it as
* such (__GFP_COMP), or manually just split the page up yourself
- * (which is mainly an issue of doing "set_page_count(page, 1)" for
- * each sub-page, and then freeing them one by one when you free
- * them rather than freeing it as a compound page).
+ * (see split_page()).
*
* NOTE! Traditionally this was done with "remap_pfn_range()" which
* took an arbitrary page protection parameter. This doesn't allow
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 1029198..fc65e87 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -752,6 +752,28 @@
clear_highpage(page + i);
}
+#ifdef CONFIG_MMU
+/*
+ * split_page takes a non-compound higher-order page, and splits it into
+ * n (1<<order) sub-pages: page[0..n]
+ * Each sub-page must be freed individually.
+ *
+ * Note: this is probably too low level an operation for use in drivers.
+ * Please consult with lkml before using this in your driver.
+ */
+void split_page(struct page *page, unsigned int order)
+{
+ int i;
+
+ BUG_ON(PageCompound(page));
+ BUG_ON(!page_count(page));
+ for (i = 1; i < (1 << order); i++) {
+ BUG_ON(page_count(page + i));
+ set_page_count(page + i, 1);
+ }
+}
+#endif
+
/*
* Really, prep_compound_page() should be called from __rmqueue_bulk(). But
* we cheat by calling it from here, in the order > 0 path. Saves a branch
