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linux-next/include/linux/page-flags.h
Andy Whitcroft 91fc8ab3c6 [PATCH] page flags: add commentry regarding field reservation 
Add some documentation regarding the utilisation of the flags field in
struct page.  This field is overloaded for per page bits and to hold node,
zone and SPARSEMEM information.  Make it clear which areas are used for
what and how many bits are in each area.

Signed-off-by: Andy Whitcroft <apw@shadowen.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-04-11 06:18:32 -07:00

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/*
* Macros for manipulating and testing page->flags
*/
#ifndef PAGE_FLAGS_H
#define PAGE_FLAGS_H
#include <linux/percpu.h>
#include <linux/cache.h>
#include <asm/pgtable.h>
/*
* Various page->flags bits:
*
* PG_reserved is set for special pages, which can never be swapped out. Some
* of them might not even exist (eg empty_bad_page)...
*
* The PG_private bitflag is set if page->private contains a valid value.
*
* During disk I/O, PG_locked is used. This bit is set before I/O and
* reset when I/O completes. page_waitqueue(page) is a wait queue of all tasks
* waiting for the I/O on this page to complete.
*
* PG_uptodate tells whether the page's contents is valid. When a read
* completes, the page becomes uptodate, unless a disk I/O error happened.
*
* For choosing which pages to swap out, inode pages carry a PG_referenced bit,
* which is set any time the system accesses that page through the (mapping,
* index) hash table. This referenced bit, together with the referenced bit
* in the page tables, is used to manipulate page->age and move the page across
* the active, inactive_dirty and inactive_clean lists.
*
* Note that the referenced bit, the page->lru list_head and the active,
* inactive_dirty and inactive_clean lists are protected by the
* zone->lru_lock, and *NOT* by the usual PG_locked bit!
*
* PG_error is set to indicate that an I/O error occurred on this page.
*
* PG_arch_1 is an architecture specific page state bit. The generic code
* guarantees that this bit is cleared for a page when it first is entered into
* the page cache.
*
* PG_highmem pages are not permanently mapped into the kernel virtual address
* space, they need to be kmapped separately for doing IO on the pages. The
* struct page (these bits with information) are always mapped into kernel
* address space...
*/
/*
* Don't use the *_dontuse flags. Use the macros. Otherwise you'll break
* locked- and dirty-page accounting.
*
* The page flags field is split into two parts, the main flags area
* which extends from the low bits upwards, and the fields area which
* extends from the high bits downwards.
*
* | FIELD | ... | FLAGS |
* N-1 ^ 0
* (N-FLAGS_RESERVED)
*
* The fields area is reserved for fields mapping zone, node and SPARSEMEM
* section. The boundry between these two areas is defined by
* FLAGS_RESERVED which defines the width of the fields section
* (see linux/mmzone.h). New flags must _not_ overlap with this area.
*/
#define PG_locked 0 /* Page is locked. Don't touch. */
#define PG_error 1
#define PG_referenced 2
#define PG_uptodate 3
#define PG_dirty 4
#define PG_lru 5
#define PG_active 6
#define PG_slab 7 /* slab debug (Suparna wants this) */
#define PG_checked 8 /* kill me in 2.5.<early>. */
#define PG_arch_1 9
#define PG_reserved 10
#define PG_private 11 /* Has something at ->private */
#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 /* Free, should not be written */
#define PG_buddy 19 /* Page is free, on buddy lists */
#define PG_uncached 20 /* Page has been mapped as uncached */
/*
* Global page accounting. One instance per CPU. Only unsigned longs are
* allowed.
*
* - Fields can be modified with xxx_page_state and xxx_page_state_zone at
* any time safely (which protects the instance from modification by
* interrupt.
* - The __xxx_page_state variants can be used safely when interrupts are
* disabled.
* - The __xxx_page_state variants can be used if the field is only
* modified from process context and protected from preemption, or only
* modified from interrupt context. In this case, the field should be
* commented here.
*/
struct page_state {
unsigned long nr_dirty; /* Dirty writeable pages */
unsigned long nr_writeback; /* Pages under writeback */
unsigned long nr_unstable; /* NFS unstable pages */
unsigned long nr_page_table_pages;/* Pages used for pagetables */
unsigned long nr_mapped; /* mapped into pagetables.
* only modified from process context */
unsigned long nr_slab; /* In slab */
#define GET_PAGE_STATE_LAST nr_slab
/*
* The below are zeroed by get_page_state(). Use get_full_page_state()
* to add up all these.
*/
unsigned long pgpgin; /* Disk reads */
unsigned long pgpgout; /* Disk writes */
unsigned long pswpin; /* swap reads */
unsigned long pswpout; /* swap writes */
unsigned long pgalloc_high; /* page allocations */
unsigned long pgalloc_normal;
unsigned long pgalloc_dma32;
unsigned long pgalloc_dma;
unsigned long pgfree; /* page freeings */
unsigned long pgactivate; /* pages moved inactive->active */
unsigned long pgdeactivate; /* pages moved active->inactive */
unsigned long pgfault; /* faults (major+minor) */
unsigned long pgmajfault; /* faults (major only) */
unsigned long pgrefill_high; /* inspected in refill_inactive_zone */
unsigned long pgrefill_normal;
unsigned long pgrefill_dma32;
unsigned long pgrefill_dma;
unsigned long pgsteal_high; /* total highmem pages reclaimed */
unsigned long pgsteal_normal;
unsigned long pgsteal_dma32;
unsigned long pgsteal_dma;
unsigned long pgscan_kswapd_high;/* total highmem pages scanned */
unsigned long pgscan_kswapd_normal;
unsigned long pgscan_kswapd_dma32;
unsigned long pgscan_kswapd_dma;
unsigned long pgscan_direct_high;/* total highmem pages scanned */
unsigned long pgscan_direct_normal;
unsigned long pgscan_direct_dma32;
unsigned long pgscan_direct_dma;
unsigned long pginodesteal; /* pages reclaimed via inode freeing */
unsigned long slabs_scanned; /* slab objects scanned */
unsigned long kswapd_steal; /* pages reclaimed by kswapd */
unsigned long kswapd_inodesteal;/* reclaimed via kswapd inode freeing */
unsigned long pageoutrun; /* kswapd's calls to page reclaim */
unsigned long allocstall; /* direct reclaim calls */
unsigned long pgrotated; /* pages rotated to tail of the LRU */
unsigned long nr_bounce; /* pages for bounce buffers */
};
extern void get_page_state(struct page_state *ret);
extern void get_page_state_node(struct page_state *ret, int node);
extern void get_full_page_state(struct page_state *ret);
extern unsigned long read_page_state_offset(unsigned long offset);
extern void mod_page_state_offset(unsigned long offset, unsigned long delta);
extern void __mod_page_state_offset(unsigned long offset, unsigned long delta);
#define read_page_state(member) \
read_page_state_offset(offsetof(struct page_state, member))
#define mod_page_state(member, delta) \
mod_page_state_offset(offsetof(struct page_state, member), (delta))
#define __mod_page_state(member, delta) \
__mod_page_state_offset(offsetof(struct page_state, member), (delta))
#define inc_page_state(member) mod_page_state(member, 1UL)
#define dec_page_state(member) mod_page_state(member, 0UL - 1)
#define add_page_state(member,delta) mod_page_state(member, (delta))
#define sub_page_state(member,delta) mod_page_state(member, 0UL - (delta))
#define __inc_page_state(member) __mod_page_state(member, 1UL)
#define __dec_page_state(member) __mod_page_state(member, 0UL - 1)
#define __add_page_state(member,delta) __mod_page_state(member, (delta))
#define __sub_page_state(member,delta) __mod_page_state(member, 0UL - (delta))
#define page_state(member) (*__page_state(offsetof(struct page_state, member)))
#define state_zone_offset(zone, member) \
({ \
unsigned offset; \
if (is_highmem(zone)) \
offset = offsetof(struct page_state, member##_high); \
else if (is_normal(zone)) \
offset = offsetof(struct page_state, member##_normal); \
else if (is_dma32(zone)) \
offset = offsetof(struct page_state, member##_dma32); \
else \
offset = offsetof(struct page_state, member##_dma); \
offset; \
})
#define __mod_page_state_zone(zone, member, delta) \
do { \
__mod_page_state_offset(state_zone_offset(zone, member), (delta)); \
} while (0)
#define mod_page_state_zone(zone, member, delta) \
do { \
mod_page_state_offset(state_zone_offset(zone, member), (delta)); \
} while (0)
/*
* Manipulation of page state flags
*/
#define PageLocked(page) \
test_bit(PG_locked, &(page)->flags)
#define SetPageLocked(page) \
set_bit(PG_locked, &(page)->flags)
#define TestSetPageLocked(page) \
test_and_set_bit(PG_locked, &(page)->flags)
#define ClearPageLocked(page) \
clear_bit(PG_locked, &(page)->flags)
#define TestClearPageLocked(page) \
test_and_clear_bit(PG_locked, &(page)->flags)
#define PageError(page) test_bit(PG_error, &(page)->flags)
#define SetPageError(page) set_bit(PG_error, &(page)->flags)
#define ClearPageError(page) clear_bit(PG_error, &(page)->flags)
#define PageReferenced(page) test_bit(PG_referenced, &(page)->flags)
#define SetPageReferenced(page) set_bit(PG_referenced, &(page)->flags)
#define ClearPageReferenced(page) clear_bit(PG_referenced, &(page)->flags)
#define TestClearPageReferenced(page) test_and_clear_bit(PG_referenced, &(page)->flags)
#define PageUptodate(page) test_bit(PG_uptodate, &(page)->flags)
#ifndef SetPageUptodate
#define SetPageUptodate(page) set_bit(PG_uptodate, &(page)->flags)
#endif
#define ClearPageUptodate(page) clear_bit(PG_uptodate, &(page)->flags)
#define PageDirty(page) test_bit(PG_dirty, &(page)->flags)
#define SetPageDirty(page) set_bit(PG_dirty, &(page)->flags)
#define TestSetPageDirty(page) test_and_set_bit(PG_dirty, &(page)->flags)
#define ClearPageDirty(page) clear_bit(PG_dirty, &(page)->flags)
#define __ClearPageDirty(page) __clear_bit(PG_dirty, &(page)->flags)
#define TestClearPageDirty(page) test_and_clear_bit(PG_dirty, &(page)->flags)
#define PageLRU(page) test_bit(PG_lru, &(page)->flags)
#define SetPageLRU(page) set_bit(PG_lru, &(page)->flags)
#define ClearPageLRU(page) clear_bit(PG_lru, &(page)->flags)
#define __ClearPageLRU(page) __clear_bit(PG_lru, &(page)->flags)
#define PageActive(page) test_bit(PG_active, &(page)->flags)
#define SetPageActive(page) set_bit(PG_active, &(page)->flags)
#define ClearPageActive(page) clear_bit(PG_active, &(page)->flags)
#define __ClearPageActive(page) __clear_bit(PG_active, &(page)->flags)
#define PageSlab(page) test_bit(PG_slab, &(page)->flags)
#define __SetPageSlab(page) __set_bit(PG_slab, &(page)->flags)
#define __ClearPageSlab(page) __clear_bit(PG_slab, &(page)->flags)
#ifdef CONFIG_HIGHMEM
#define PageHighMem(page) is_highmem(page_zone(page))
#else
#define PageHighMem(page) 0 /* needed to optimize away at compile time */
#endif
#define PageChecked(page) test_bit(PG_checked, &(page)->flags)
#define SetPageChecked(page) set_bit(PG_checked, &(page)->flags)
#define ClearPageChecked(page) clear_bit(PG_checked, &(page)->flags)
#define PageReserved(page) test_bit(PG_reserved, &(page)->flags)
#define SetPageReserved(page) set_bit(PG_reserved, &(page)->flags)
#define ClearPageReserved(page) clear_bit(PG_reserved, &(page)->flags)
#define __ClearPageReserved(page) __clear_bit(PG_reserved, &(page)->flags)
#define SetPagePrivate(page) set_bit(PG_private, &(page)->flags)
#define ClearPagePrivate(page) clear_bit(PG_private, &(page)->flags)
#define PagePrivate(page) test_bit(PG_private, &(page)->flags)
#define __SetPagePrivate(page) __set_bit(PG_private, &(page)->flags)
#define __ClearPagePrivate(page) __clear_bit(PG_private, &(page)->flags)
#define PageWriteback(page) test_bit(PG_writeback, &(page)->flags)
#define SetPageWriteback(page) \
do { \
if (!test_and_set_bit(PG_writeback, \
&(page)->flags)) \
inc_page_state(nr_writeback); \
} while (0)
#define TestSetPageWriteback(page) \
({ \
int ret; \
ret = test_and_set_bit(PG_writeback, \
&(page)->flags); \
if (!ret) \
inc_page_state(nr_writeback); \
ret; \
})
#define ClearPageWriteback(page) \
do { \
if (test_and_clear_bit(PG_writeback, \
&(page)->flags)) \
dec_page_state(nr_writeback); \
} while (0)
#define TestClearPageWriteback(page) \
({ \
int ret; \
ret = test_and_clear_bit(PG_writeback, \
&(page)->flags); \
if (ret) \
dec_page_state(nr_writeback); \
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)
#define PageMappedToDisk(page) test_bit(PG_mappedtodisk, &(page)->flags)
#define SetPageMappedToDisk(page) set_bit(PG_mappedtodisk, &(page)->flags)
#define ClearPageMappedToDisk(page) clear_bit(PG_mappedtodisk, &(page)->flags)
#define PageReclaim(page) test_bit(PG_reclaim, &(page)->flags)
#define SetPageReclaim(page) set_bit(PG_reclaim, &(page)->flags)
#define ClearPageReclaim(page) clear_bit(PG_reclaim, &(page)->flags)
#define TestClearPageReclaim(page) test_and_clear_bit(PG_reclaim, &(page)->flags)
#define PageCompound(page) test_bit(PG_compound, &(page)->flags)
#define __SetPageCompound(page) __set_bit(PG_compound, &(page)->flags)
#define __ClearPageCompound(page) __clear_bit(PG_compound, &(page)->flags)
#ifdef CONFIG_SWAP
#define PageSwapCache(page) test_bit(PG_swapcache, &(page)->flags)
#define SetPageSwapCache(page) set_bit(PG_swapcache, &(page)->flags)
#define ClearPageSwapCache(page) clear_bit(PG_swapcache, &(page)->flags)
#else
#define PageSwapCache(page) 0
#endif
#define PageUncached(page) test_bit(PG_uncached, &(page)->flags)
#define SetPageUncached(page) set_bit(PG_uncached, &(page)->flags)
#define ClearPageUncached(page) clear_bit(PG_uncached, &(page)->flags)
struct page; /* forward declaration */
int test_clear_page_dirty(struct page *page);
int test_clear_page_writeback(struct page *page);
int test_set_page_writeback(struct page *page);
static inline void clear_page_dirty(struct page *page)
{
test_clear_page_dirty(page);
}
static inline void set_page_writeback(struct page *page)
{
test_set_page_writeback(page);
}
#endif /* PAGE_FLAGS_H */
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