From d85f33855c303acfa87fa457157cef755b6087df Mon Sep 17 00:00:00 2001 From: Christoph Lameter Date: Sun, 6 May 2007 14:49:39 -0700 Subject: Make page->private usable in compound pages If we add a new flag so that we can distinguish between the first page and the tail pages then we can avoid to use page->private in the first page. page->private == page for the first page, so there is no real information in there. Freeing up page->private makes the use of compound pages more transparent. They become more usable like real pages. Right now we have to be careful f.e. if we are going beyond PAGE_SIZE allocations in the slab on i386 because we can then no longer use the private field. This is one of the issues that cause us not to support debugging for page size slabs in SLAB. Having page->private available for SLUB would allow more meta information in the page struct. I can probably avoid the 16 bit ints that I have in there right now. Also if page->private is available then a compound page may be equipped with buffer heads. This may free up the way for filesystems to support larger blocks than page size. We add PageTail as an alias of PageReclaim. Compound pages cannot currently be reclaimed. Because of the alias one needs to check PageCompound first. The RFC for the this approach was discussed at http://marc.info/?t=117574302800001&r=1&w=2 [nacc@us.ibm.com: fix hugetlbfs] Signed-off-by: Christoph Lameter Signed-off-by: Nishanth Aravamudan Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/page-flags.h | 14 ++++++++++++++ 1 file changed, 14 insertions(+) (limited to 'include/linux/page-flags.h') diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h index 96326594e55d..a1e143634946 100644 --- a/include/linux/page-flags.h +++ b/include/linux/page-flags.h @@ -94,6 +94,12 @@ /* 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 @@ -241,6 +247,14 @@ static inline void SetPageUptodate(struct page *page) #define __SetPageCompound(page) __set_bit(PG_compound, &(page)->flags) #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. + */ +#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) + #ifdef CONFIG_SWAP #define PageSwapCache(page) test_bit(PG_swapcache, &(page)->flags) #define SetPageSwapCache(page) set_bit(PG_swapcache, &(page)->flags) -- cgit v1.2.2 From 6d7779538f765963ced45a3fa4bed7ba8d2c277d Mon Sep 17 00:00:00 2001 From: Christoph Lameter Date: Sun, 6 May 2007 14:49:40 -0700 Subject: mm: optimize compound_head() by avoiding a shared page flag 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 Signed-off-by: Linus Torvalds --- include/linux/page-flags.h | 37 ++++++++++++++++++++++++++----------- 1 file changed, 26 insertions(+), 11 deletions(-) (limited to 'include/linux/page-flags.h') diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h index a1e143634946..a3c8b60a9c3a 100644 --- a/include/linux/page-flags.h +++ b/include/linux/page-flags.h @@ -6,6 +6,7 @@ #define PAGE_FLAGS_H #include +#include /* * 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(struct page *page) #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) -- cgit v1.2.2 From 04293355ac9dbe81bd01b89ca2adb58be34c2c60 Mon Sep 17 00:00:00 2001 From: "Rafael J. Wysocki" Date: Sun, 6 May 2007 14:50:43 -0700 Subject: mm: remove unused page flags Remove the two page flags that were previously used by swsusp and are no longer needed. Signed-off-by: Rafael J. Wysocki Acked-by: Pavel Machek Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/page-flags.h | 12 ------------ 1 file changed, 12 deletions(-) (limited to 'include/linux/page-flags.h') diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h index a3c8b60a9c3a..ae2d79f2107e 100644 --- a/include/linux/page-flags.h +++ b/include/linux/page-flags.h @@ -83,13 +83,11 @@ #define PG_private 11 /* If pagecache, has fs-private data */ #define PG_writeback 12 /* Page is under writeback */ -#define PG_nosave 13 /* Used for system suspend/resume */ #define PG_compound 14 /* Part of a compound page */ #define PG_swapcache 15 /* Swap page: swp_entry_t in private */ #define PG_mappedtodisk 16 /* Has blocks allocated on-disk */ #define PG_reclaim 17 /* To be reclaimed asap */ -#define PG_nosave_free 18 /* Used for system suspend/resume */ #define PG_buddy 19 /* Page is free, on buddy lists */ /* PG_owner_priv_1 users should have descriptive aliases */ @@ -215,16 +213,6 @@ static inline void SetPageUptodate(struct page *page) ret; \ }) -#define PageNosave(page) test_bit(PG_nosave, &(page)->flags) -#define SetPageNosave(page) set_bit(PG_nosave, &(page)->flags) -#define TestSetPageNosave(page) test_and_set_bit(PG_nosave, &(page)->flags) -#define ClearPageNosave(page) clear_bit(PG_nosave, &(page)->flags) -#define TestClearPageNosave(page) test_and_clear_bit(PG_nosave, &(page)->flags) - -#define PageNosaveFree(page) test_bit(PG_nosave_free, &(page)->flags) -#define SetPageNosaveFree(page) set_bit(PG_nosave_free, &(page)->flags) -#define ClearPageNosaveFree(page) clear_bit(PG_nosave_free, &(page)->flags) - #define PageBuddy(page) test_bit(PG_buddy, &(page)->flags) #define __SetPageBuddy(page) __set_bit(PG_buddy, &(page)->flags) #define __ClearPageBuddy(page) __clear_bit(PG_buddy, &(page)->flags) -- cgit v1.2.2