The patch titled
Optimize compound_head() by avoiding a shared page flag
has been added to the -mm tree. Its filename is
optimize-compound_head-by-avoiding-a-shared-page.patch
*** Remember to use Documentation/SubmitChecklist when testing your code ***
See http://www.zip.com.au/~akpm/linux/patches/stuff/added-to-mm.txt to find
out what to do about this
------------------------------------------------------
Subject: Optimize compound_head() by avoiding a shared page flag
From: Christoph Lameter <clameter@xxxxxxx>
The patch adds PageTail(page) and PageHead(page) to check if a page is the
head or the tail of a compound page. This is done by masking the two bits
describing the state of a compound page and then comparing them. So one
comparision and a branch instead of two bit checks and two branches.
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/mm.h | 11 +---------
include/linux/page-flags.h | 37 ++++++++++++++++++++++++-----------
mm/page_alloc.c | 10 +++------
3 files changed, 32 insertions(+), 26 deletions(-)
diff -puN include/linux/mm.h~optimize-compound_head-by-avoiding-a-shared-page include/linux/mm.h
--- a/include/linux/mm.h~optimize-compound_head-by-avoiding-a-shared-page
+++ a/include/linux/mm.h
@@ -296,14 +296,7 @@ static inline int get_page_unless_zero(s
static inline struct page *compound_head(struct page *page)
{
- /*
- * We could avoid the PageCompound(page) check if
- * we would not overload PageTail().
- *
- * This check has to be done in several performance critical
- * paths of the slab etc. IMHO PageTail deserves its own flag.
- */
- if (unlikely(PageCompound(page) && PageTail(page)))
+ if (unlikely(PageTail(page)))
return page->first_page;
return page;
}
@@ -354,7 +347,7 @@ static inline compound_page_dtor *get_co
static inline int compound_order(struct page *page)
{
- if (!PageCompound(page) || PageTail(page))
+ if (!PageHead(page))
return 0;
return (unsigned long)page[1].lru.prev;
}
diff -puN include/linux/page-flags.h~optimize-compound_head-by-avoiding-a-shared-page include/linux/page-flags.h
--- a/include/linux/page-flags.h~optimize-compound_head-by-avoiding-a-shared-page
+++ a/include/linux/page-flags.h
@@ -6,6 +6,7 @@
#define PAGE_FLAGS_H
#include <linux/types.h>
+#include <linux/mm_types.h>
/*
* Various page->flags bits:
@@ -94,12 +95,6 @@
/* PG_owner_priv_1 users should have descriptive aliases */
#define PG_checked PG_owner_priv_1 /* Used by some filesystems */
-/*
- * Marks tail portion of a compound page. We currently do not reclaim
- * compound pages so we can reuse a flag only used for reclaim here.
- */
-#define PG_tail PG_reclaim
-
#if (BITS_PER_LONG > 32)
/*
* 64-bit-only flags build down from bit 31
@@ -248,12 +243,32 @@ static inline void SetPageUptodate(struc
#define __ClearPageCompound(page) __clear_bit(PG_compound, &(page)->flags)
/*
- * Note: PG_tail is an alias of another page flag. The result of PageTail()
- * is only valid if PageCompound(page) is true.
+ * PG_reclaim is used in combination with PG_compound to mark the
+ * head and tail of a compound page
+ *
+ * PG_compound & PG_reclaim => Tail page
+ * PG_compound & ~PG_reclaim => Head page
*/
-#define PageTail(page) test_bit(PG_tail, &(page)->flags)
-#define __SetPageTail(page) __set_bit(PG_tail, &(page)->flags)
-#define __ClearPageTail(page) __clear_bit(PG_tail, &(page)->flags)
+
+#define PG_head_tail_mask ((1L << PG_compound) | (1L << PG_reclaim))
+
+#define PageTail(page) ((page->flags & PG_head_tail_mask) \
+ == PG_head_tail_mask)
+
+static inline void __SetPageTail(struct page *page)
+{
+ page->flags |= PG_head_tail_mask;
+}
+
+static inline void __ClearPageTail(struct page *page)
+{
+ page->flags &= ~PG_head_tail_mask;
+}
+
+#define PageHead(page) ((page->flags & PG_head_tail_mask) \
+ == (1L << PG_compound))
+#define __SetPageHead(page) __SetPageCompound(page)
+#define __ClearPageHead(page) __ClearPageCompound(page)
#ifdef CONFIG_SWAP
#define PageSwapCache(page) test_bit(PG_swapcache, &(page)->flags)
diff -puN mm/page_alloc.c~optimize-compound_head-by-avoiding-a-shared-page mm/page_alloc.c
--- a/mm/page_alloc.c~optimize-compound_head-by-avoiding-a-shared-page
+++ a/mm/page_alloc.c
@@ -285,12 +285,11 @@ static void prep_compound_page(struct pa
set_compound_page_dtor(page, free_compound_page);
set_compound_order(page, order);
- __SetPageCompound(page);
+ __SetPageHead(page);
for (i = 1; i < nr_pages; i++) {
struct page *p = page + i;
__SetPageTail(p);
- __SetPageCompound(p);
p->first_page = page;
}
}
@@ -303,17 +302,16 @@ static void destroy_compound_page(struct
if (unlikely(compound_order(page) != order))
bad_page(page);
- if (unlikely(!PageCompound(page)))
+ if (unlikely(!PageHead(page)))
bad_page(page);
- __ClearPageCompound(page);
+ __ClearPageHead(page);
for (i = 1; i < nr_pages; i++) {
struct page *p = page + i;
- if (unlikely(!PageCompound(p) | !PageTail(p) |
+ if (unlikely(!PageTail(p) |
(p->first_page != page)))
bad_page(page);
__ClearPageTail(p);
- __ClearPageCompound(p);
}
}
_
Patches currently in -mm which might be from clameter@xxxxxxx are
slab-introduce-krealloc.patch
slab-introduce-krealloc-fix.patch
paravirt_ops-allow-paravirt-backend-to-choose-kernel-pmd-sharing.patch
add-apply_to_page_range-which-applies-a-function-to-a-pte-range.patch
safer-nr_node_ids-and-nr_node_ids-determination-and-initial.patch
use-zvc-counters-to-establish-exact-size-of-dirtyable-pages.patch
slab-ensure-cache_alloc_refill-terminates.patch
smaps-extract-pmd-walker-from-smaps-code.patch
smaps-add-pages-referenced-count-to-smaps.patch
smaps-add-clear_refs-file-to-clear-reference.patch
smaps-add-clear_refs-file-to-clear-reference-fix.patch
smaps-add-clear_refs-file-to-clear-reference-fix-fix.patch
slab-use-num_possible_cpus-in-enable_cpucache.patch
i386-use-page-allocator-to-allocate-thread_info-structure.patch
slub-core.patch
slub-fix-numa-bootstrap.patch
slub-use-correct-flags-to-check-for-dma-cache.patch
slub-treat-slab_hwcache_align-as-a-mininum-and-not-as-the-alignment.patch
slub-add-slabinfo-tool.patch
make-page-private-usable-in-compound-pages-v1.patch
optimize-compound_head-by-avoiding-a-shared-page.patch
add-virt_to_head_page-and-consolidate-code-in-slab-and-slub.patch
quicklists-for-page-table-pages.patch
quicklist-support-for-ia64.patch
quicklist-support-for-x86_64.patch
quicklist-support-for-sparc64.patch
extend-print_symbol-capability-fix.patch
slab-shutdown-cache_reaper-when-cpu-goes-down.patch
mm-implement-swap-prefetching.patch
readahead-state-based-method-aging-accounting.patch
-
To unsubscribe from this list: send the line "unsubscribe mm-commits" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
