kernel-ark/include/linux/page-flags.h
Christoph Lameter e20b8cca76 PAGEFLAGS_EXTENDED and separate page flags for Head and Tail
Having separate page flags for the head and the tail of a compound page allows
the compiler to use bitops instead of operations on a word to check for a tail
page.  That is f.e.  important for virt_to_head_page() which is used in
various critical code paths (kfree for example):

Code for PageTail(page)

Before:

 mov    (%rdi),%rdx		page->flags
 mov    %rdx,%rax		3 bytes
 and    $0x12000,%eax		5 bytes
 cmp    $0x12000,%rax		6 bytes
 je     897 <kfree+0xa7>

After:

 mov    (%rdi),%rax
 test   $0x40,%ah			(3 bytes)
 jne    887 <kfree+0x97>

So we go from 14 bytes to 3 bytes and from 3 instructions to one.  From the
use of 2 registers we go to none.

We can only use page flags for this if we have page flags available.  This
patch introduces CONFIG_PAGEFLAGS_EXTENDED that is set if pageflags are not
scarce due to SPARSEMEM using page flags for its sectionid on 32 bit NUMA
platforms.

Additional page flag definitions can be added to the CONFIG_PAGEFLAGS_EXTENDED
section in page-flags.h if the functionality depends on PAGEFLAGS_EXTENDED or
if more page flag overlapping tricks are used for the !PAGEFLAGS_EXTENDED
fallback (the upcoming virtual compound patch may hook in here and Rik's/Lee's
additional page flags to solve the reclaim issues could also be added there
[hint...  hint...  where are these patchsets?]).

Avoiding the overlaying of Pg_reclaim also clears the way for possible use of
compound pages for the pagecache or on the LRU.

Signed-off-by: Christoph Lameter <clameter@sgi.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2008-04-28 08:58:22 -07:00

311 lines
9.4 KiB
C

/*
* Macros for manipulating and testing page->flags
*/
#ifndef PAGE_FLAGS_H
#define PAGE_FLAGS_H
#include <linux/types.h>
#ifndef __GENERATING_BOUNDS_H
#include <linux/mm_types.h>
#include <linux/bounds.h>
#endif /* !__GENERATING_BOUNDS_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 on pagecache pages if they contain filesystem
* specific data (which is normally at page->private). It can be used by
* private allocations for its own usage.
*
* During initiation of disk I/O, PG_locked is set. This bit is set before I/O
* and cleared when writeback _starts_ or when read _completes_. PG_writeback
* is set before writeback starts and cleared when it finishes.
*
* PG_locked also pins a page in pagecache, and blocks truncation of the file
* while it is held.
*
* page_waitqueue(page) is a wait queue of all tasks waiting for the page
* to become unlocked.
*
* 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.
*
* PG_referenced, PG_reclaim are used for page reclaim for anonymous and
* file-backed pagecache (see mm/vmscan.c).
*
* 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...
*
* PG_buddy is set to indicate that the page is free and in the buddy system
* (see mm/page_alloc.c).
*
*/
/*
* 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
* (NR_PAGEFLAGS)
*
* The fields area is reserved for fields mapping zone, node (for NUMA) and
* SPARSEMEM section (for variants of SPARSEMEM that require section ids like
* SPARSEMEM_EXTREME with !SPARSEMEM_VMEMMAP).
*/
enum pageflags {
PG_locked, /* Page is locked. Don't touch. */
PG_error,
PG_referenced,
PG_uptodate,
PG_dirty,
PG_lru,
PG_active,
PG_slab,
PG_owner_priv_1, /* Owner use. If pagecache, fs may use*/
PG_arch_1,
PG_reserved,
PG_private, /* If pagecache, has fs-private data */
PG_writeback, /* Page is under writeback */
#ifdef CONFIG_PAGEFLAGS_EXTENDED
PG_head, /* A head page */
PG_tail, /* A tail page */
#else
PG_compound, /* A compound page */
#endif
PG_swapcache, /* Swap page: swp_entry_t in private */
PG_mappedtodisk, /* Has blocks allocated on-disk */
PG_reclaim, /* To be reclaimed asap */
PG_buddy, /* Page is free, on buddy lists */
#ifdef CONFIG_IA64_UNCACHED_ALLOCATOR
PG_uncached, /* Page has been mapped as uncached */
#endif
__NR_PAGEFLAGS
};
#ifndef __GENERATING_BOUNDS_H
/*
* Macros to create function definitions for page flags
*/
#define TESTPAGEFLAG(uname, lname) \
static inline int Page##uname(struct page *page) \
{ return test_bit(PG_##lname, &page->flags); }
#define SETPAGEFLAG(uname, lname) \
static inline void SetPage##uname(struct page *page) \
{ set_bit(PG_##lname, &page->flags); }
#define CLEARPAGEFLAG(uname, lname) \
static inline void ClearPage##uname(struct page *page) \
{ clear_bit(PG_##lname, &page->flags); }
#define __SETPAGEFLAG(uname, lname) \
static inline void __SetPage##uname(struct page *page) \
{ __set_bit(PG_##lname, &page->flags); }
#define __CLEARPAGEFLAG(uname, lname) \
static inline void __ClearPage##uname(struct page *page) \
{ __clear_bit(PG_##lname, &page->flags); }
#define TESTSETFLAG(uname, lname) \
static inline int TestSetPage##uname(struct page *page) \
{ return test_and_set_bit(PG_##lname, &page->flags); }
#define TESTCLEARFLAG(uname, lname) \
static inline int TestClearPage##uname(struct page *page) \
{ return test_and_clear_bit(PG_##lname, &page->flags); }
#define PAGEFLAG(uname, lname) TESTPAGEFLAG(uname, lname) \
SETPAGEFLAG(uname, lname) CLEARPAGEFLAG(uname, lname)
#define __PAGEFLAG(uname, lname) TESTPAGEFLAG(uname, lname) \
__SETPAGEFLAG(uname, lname) __CLEARPAGEFLAG(uname, lname)
#define PAGEFLAG_FALSE(uname) \
static inline int Page##uname(struct page *page) \
{ return 0; }
#define TESTSCFLAG(uname, lname) \
TESTSETFLAG(uname, lname) TESTCLEARFLAG(uname, lname)
struct page; /* forward declaration */
PAGEFLAG(Locked, locked) TESTSCFLAG(Locked, locked)
PAGEFLAG(Error, error)
PAGEFLAG(Referenced, referenced) TESTCLEARFLAG(Referenced, referenced)
PAGEFLAG(Dirty, dirty) TESTSCFLAG(Dirty, dirty) __CLEARPAGEFLAG(Dirty, dirty)
PAGEFLAG(LRU, lru) __CLEARPAGEFLAG(LRU, lru)
PAGEFLAG(Active, active) __CLEARPAGEFLAG(Active, active)
__PAGEFLAG(Slab, slab)
PAGEFLAG(Checked, owner_priv_1) /* Used by some filesystems */
PAGEFLAG(Pinned, owner_priv_1) TESTSCFLAG(Pinned, owner_priv_1) /* Xen */
PAGEFLAG(Reserved, reserved) __CLEARPAGEFLAG(Reserved, reserved)
PAGEFLAG(Private, private) __CLEARPAGEFLAG(Private, private)
__SETPAGEFLAG(Private, private)
/*
* Only test-and-set exist for PG_writeback. The unconditional operators are
* risky: they bypass page accounting.
*/
TESTPAGEFLAG(Writeback, writeback) TESTSCFLAG(Writeback, writeback)
__PAGEFLAG(Buddy, buddy)
PAGEFLAG(MappedToDisk, mappedtodisk)
/* PG_readahead is only used for file reads; PG_reclaim is only for writes */
PAGEFLAG(Reclaim, reclaim) TESTCLEARFLAG(Reclaim, reclaim)
PAGEFLAG(Readahead, reclaim) /* Reminder to do async read-ahead */
#ifdef CONFIG_HIGHMEM
/*
* Must use a macro here due to header dependency issues. page_zone() is not
* available at this point.
*/
#define PageHighMem(__p) is_highmem(page_zone(__p))
#else
PAGEFLAG_FALSE(HighMem)
#endif
#ifdef CONFIG_SWAP
PAGEFLAG(SwapCache, swapcache)
#else
PAGEFLAG_FALSE(SwapCache)
#endif
#ifdef CONFIG_IA64_UNCACHED_ALLOCATOR
PAGEFLAG(Uncached, uncached)
#else
PAGEFLAG_FALSE(Uncached)
#endif
static inline int PageUptodate(struct page *page)
{
int ret = test_bit(PG_uptodate, &(page)->flags);
/*
* Must ensure that the data we read out of the page is loaded
* _after_ we've loaded page->flags to check for PageUptodate.
* We can skip the barrier if the page is not uptodate, because
* we wouldn't be reading anything from it.
*
* See SetPageUptodate() for the other side of the story.
*/
if (ret)
smp_rmb();
return ret;
}
static inline void __SetPageUptodate(struct page *page)
{
smp_wmb();
__set_bit(PG_uptodate, &(page)->flags);
#ifdef CONFIG_S390
page_clear_dirty(page);
#endif
}
static inline void SetPageUptodate(struct page *page)
{
#ifdef CONFIG_S390
if (!test_and_set_bit(PG_uptodate, &page->flags))
page_clear_dirty(page);
#else
/*
* Memory barrier must be issued before setting the PG_uptodate bit,
* so that all previous stores issued in order to bring the page
* uptodate are actually visible before PageUptodate becomes true.
*
* s390 doesn't need an explicit smp_wmb here because the test and
* set bit already provides full barriers.
*/
smp_wmb();
set_bit(PG_uptodate, &(page)->flags);
#endif
}
CLEARPAGEFLAG(Uptodate, uptodate)
extern void cancel_dirty_page(struct page *page, unsigned int account_size);
int test_clear_page_writeback(struct page *page);
int test_set_page_writeback(struct page *page);
static inline void set_page_writeback(struct page *page)
{
test_set_page_writeback(page);
}
#ifdef CONFIG_PAGEFLAGS_EXTENDED
/*
* System with lots of page flags available. This allows separate
* flags for PageHead() and PageTail() checks of compound pages so that bit
* tests can be used in performance sensitive paths. PageCompound is
* generally not used in hot code paths.
*/
__PAGEFLAG(Head, head)
__PAGEFLAG(Tail, tail)
static inline int PageCompound(struct page *page)
{
return page->flags & ((1L << PG_head) | (1L << PG_tail));
}
#else
/*
* Reduce page flag use as much as possible by overlapping
* compound page flags with the flags used for page cache pages. Possible
* because PageCompound is always set for compound pages and not for
* pages on the LRU and/or pagecache.
*/
TESTPAGEFLAG(Compound, compound)
__PAGEFLAG(Head, compound)
/*
* PG_reclaim is used in combination with PG_compound to mark the
* head and tail of a compound page. This saves one page flag
* but makes it impossible to use compound pages for the page cache.
* The PG_reclaim bit would have to be used for reclaim or readahead
* if compound pages enter the page cache.
*
* PG_compound & PG_reclaim => Tail page
* PG_compound & ~PG_reclaim => Head page
*/
#define PG_head_tail_mask ((1L << PG_compound) | (1L << PG_reclaim))
static inline int PageTail(struct page *page)
{
return ((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;
}
#endif /* !PAGEFLAGS_EXTENDED */
#endif /* !__GENERATING_BOUNDS_H */
#endif /* PAGE_FLAGS_H */