linux-stable/include/linux/pagemap.h
Steven Rostedt 088e54658f mm: remove likely() from mapping_unevictable()
The mapping_unevictable() has a likely() around the mapping parameter.
This mapping parameter comes from page_mapping() which has an unlikely()
that the page will be set as PAGE_MAPPING_ANON, and if so, it will return
NULL.  One would think that this unlikely() means that the mapping
returned by page_mapping() would not be NULL, but where page_mapping() is
used just above mapping_unevictable(), that unlikely() is incorrect most
of the time.  This means that the "likely(mapping)" in
mapping_unevictable() is incorrect most of the time.

Running the annotated branch profiler on my main box which runs firefox,
evolution, xchat and is part of my distcc farm, I had this:

 correct incorrect  %        Function                  File              Line
 ------- ---------  -        --------                  ----              ----
12872836 1269443893  98 mapping_unevictable            pagemap.h            51
35935762 1270265395  97 page_mapping                   mm.h                 659
1306198001   143659   0 page_mapping                   mm.h                 657
203131478   121586   0 page_mapping                   mm.h                 657
 5415491     1116   0 page_mapping                   mm.h                 657
74899487     1116   0 page_mapping                   mm.h                 657
203132845      224   0 page_mapping                   mm.h                 659
 5415464       27   0 page_mapping                   mm.h                 659
   13552        0   0 page_mapping                   mm.h                 657
   13552        0   0 page_mapping                   mm.h                 659
  242630        0   0 page_mapping                   mm.h                 657
  242630        0   0 page_mapping                   mm.h                 659
74899487        0   0 page_mapping                   mm.h                 659

The page_mapping() is a static inline, which is why it shows up multiple
times.  The mapping_unevictable() is also a static inline but seems to be
used only once in my setup.

The unlikely in page_mapping() was correct a total of 1909540379 times and
incorrect 1270533123 times, with a 39% being incorrect.  Perhaps this is
enough to remove the unlikely from page_mapping() as well.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Acked-by: Nick Piggin <npiggin@kernel.dk>
Acked-by: Rik van Riel <riel@redhat.com>
Cc: Lee Schermerhorn <Lee.Schermerhorn@hp.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2011-01-13 17:32:36 -08:00

477 lines
14 KiB
C

#ifndef _LINUX_PAGEMAP_H
#define _LINUX_PAGEMAP_H
/*
* Copyright 1995 Linus Torvalds
*/
#include <linux/mm.h>
#include <linux/fs.h>
#include <linux/list.h>
#include <linux/highmem.h>
#include <linux/compiler.h>
#include <asm/uaccess.h>
#include <linux/gfp.h>
#include <linux/bitops.h>
#include <linux/hardirq.h> /* for in_interrupt() */
#include <linux/hugetlb_inline.h>
/*
* Bits in mapping->flags. The lower __GFP_BITS_SHIFT bits are the page
* allocation mode flags.
*/
enum mapping_flags {
AS_EIO = __GFP_BITS_SHIFT + 0, /* IO error on async write */
AS_ENOSPC = __GFP_BITS_SHIFT + 1, /* ENOSPC on async write */
AS_MM_ALL_LOCKS = __GFP_BITS_SHIFT + 2, /* under mm_take_all_locks() */
AS_UNEVICTABLE = __GFP_BITS_SHIFT + 3, /* e.g., ramdisk, SHM_LOCK */
};
static inline void mapping_set_error(struct address_space *mapping, int error)
{
if (unlikely(error)) {
if (error == -ENOSPC)
set_bit(AS_ENOSPC, &mapping->flags);
else
set_bit(AS_EIO, &mapping->flags);
}
}
static inline void mapping_set_unevictable(struct address_space *mapping)
{
set_bit(AS_UNEVICTABLE, &mapping->flags);
}
static inline void mapping_clear_unevictable(struct address_space *mapping)
{
clear_bit(AS_UNEVICTABLE, &mapping->flags);
}
static inline int mapping_unevictable(struct address_space *mapping)
{
if (mapping)
return test_bit(AS_UNEVICTABLE, &mapping->flags);
return !!mapping;
}
static inline gfp_t mapping_gfp_mask(struct address_space * mapping)
{
return (__force gfp_t)mapping->flags & __GFP_BITS_MASK;
}
/*
* This is non-atomic. Only to be used before the mapping is activated.
* Probably needs a barrier...
*/
static inline void mapping_set_gfp_mask(struct address_space *m, gfp_t mask)
{
m->flags = (m->flags & ~(__force unsigned long)__GFP_BITS_MASK) |
(__force unsigned long)mask;
}
/*
* The page cache can done in larger chunks than
* one page, because it allows for more efficient
* throughput (it can then be mapped into user
* space in smaller chunks for same flexibility).
*
* Or rather, it _will_ be done in larger chunks.
*/
#define PAGE_CACHE_SHIFT PAGE_SHIFT
#define PAGE_CACHE_SIZE PAGE_SIZE
#define PAGE_CACHE_MASK PAGE_MASK
#define PAGE_CACHE_ALIGN(addr) (((addr)+PAGE_CACHE_SIZE-1)&PAGE_CACHE_MASK)
#define page_cache_get(page) get_page(page)
#define page_cache_release(page) put_page(page)
void release_pages(struct page **pages, int nr, int cold);
/*
* speculatively take a reference to a page.
* If the page is free (_count == 0), then _count is untouched, and 0
* is returned. Otherwise, _count is incremented by 1 and 1 is returned.
*
* This function must be called inside the same rcu_read_lock() section as has
* been used to lookup the page in the pagecache radix-tree (or page table):
* this allows allocators to use a synchronize_rcu() to stabilize _count.
*
* Unless an RCU grace period has passed, the count of all pages coming out
* of the allocator must be considered unstable. page_count may return higher
* than expected, and put_page must be able to do the right thing when the
* page has been finished with, no matter what it is subsequently allocated
* for (because put_page is what is used here to drop an invalid speculative
* reference).
*
* This is the interesting part of the lockless pagecache (and lockless
* get_user_pages) locking protocol, where the lookup-side (eg. find_get_page)
* has the following pattern:
* 1. find page in radix tree
* 2. conditionally increment refcount
* 3. check the page is still in pagecache (if no, goto 1)
*
* Remove-side that cares about stability of _count (eg. reclaim) has the
* following (with tree_lock held for write):
* A. atomically check refcount is correct and set it to 0 (atomic_cmpxchg)
* B. remove page from pagecache
* C. free the page
*
* There are 2 critical interleavings that matter:
* - 2 runs before A: in this case, A sees elevated refcount and bails out
* - A runs before 2: in this case, 2 sees zero refcount and retries;
* subsequently, B will complete and 1 will find no page, causing the
* lookup to return NULL.
*
* It is possible that between 1 and 2, the page is removed then the exact same
* page is inserted into the same position in pagecache. That's OK: the
* old find_get_page using tree_lock could equally have run before or after
* such a re-insertion, depending on order that locks are granted.
*
* Lookups racing against pagecache insertion isn't a big problem: either 1
* will find the page or it will not. Likewise, the old find_get_page could run
* either before the insertion or afterwards, depending on timing.
*/
static inline int page_cache_get_speculative(struct page *page)
{
VM_BUG_ON(in_interrupt());
#if !defined(CONFIG_SMP) && defined(CONFIG_TREE_RCU)
# ifdef CONFIG_PREEMPT
VM_BUG_ON(!in_atomic());
# endif
/*
* Preempt must be disabled here - we rely on rcu_read_lock doing
* this for us.
*
* Pagecache won't be truncated from interrupt context, so if we have
* found a page in the radix tree here, we have pinned its refcount by
* disabling preempt, and hence no need for the "speculative get" that
* SMP requires.
*/
VM_BUG_ON(page_count(page) == 0);
atomic_inc(&page->_count);
#else
if (unlikely(!get_page_unless_zero(page))) {
/*
* Either the page has been freed, or will be freed.
* In either case, retry here and the caller should
* do the right thing (see comments above).
*/
return 0;
}
#endif
VM_BUG_ON(PageTail(page));
return 1;
}
/*
* Same as above, but add instead of inc (could just be merged)
*/
static inline int page_cache_add_speculative(struct page *page, int count)
{
VM_BUG_ON(in_interrupt());
#if !defined(CONFIG_SMP) && defined(CONFIG_TREE_RCU)
# ifdef CONFIG_PREEMPT
VM_BUG_ON(!in_atomic());
# endif
VM_BUG_ON(page_count(page) == 0);
atomic_add(count, &page->_count);
#else
if (unlikely(!atomic_add_unless(&page->_count, count, 0)))
return 0;
#endif
VM_BUG_ON(PageCompound(page) && page != compound_head(page));
return 1;
}
static inline int page_freeze_refs(struct page *page, int count)
{
return likely(atomic_cmpxchg(&page->_count, count, 0) == count);
}
static inline void page_unfreeze_refs(struct page *page, int count)
{
VM_BUG_ON(page_count(page) != 0);
VM_BUG_ON(count == 0);
atomic_set(&page->_count, count);
}
#ifdef CONFIG_NUMA
extern struct page *__page_cache_alloc(gfp_t gfp);
#else
static inline struct page *__page_cache_alloc(gfp_t gfp)
{
return alloc_pages(gfp, 0);
}
#endif
static inline struct page *page_cache_alloc(struct address_space *x)
{
return __page_cache_alloc(mapping_gfp_mask(x));
}
static inline struct page *page_cache_alloc_cold(struct address_space *x)
{
return __page_cache_alloc(mapping_gfp_mask(x)|__GFP_COLD);
}
typedef int filler_t(void *, struct page *);
extern struct page * find_get_page(struct address_space *mapping,
pgoff_t index);
extern struct page * find_lock_page(struct address_space *mapping,
pgoff_t index);
extern struct page * find_or_create_page(struct address_space *mapping,
pgoff_t index, gfp_t gfp_mask);
unsigned find_get_pages(struct address_space *mapping, pgoff_t start,
unsigned int nr_pages, struct page **pages);
unsigned find_get_pages_contig(struct address_space *mapping, pgoff_t start,
unsigned int nr_pages, struct page **pages);
unsigned find_get_pages_tag(struct address_space *mapping, pgoff_t *index,
int tag, unsigned int nr_pages, struct page **pages);
struct page *grab_cache_page_write_begin(struct address_space *mapping,
pgoff_t index, unsigned flags);
/*
* Returns locked page at given index in given cache, creating it if needed.
*/
static inline struct page *grab_cache_page(struct address_space *mapping,
pgoff_t index)
{
return find_or_create_page(mapping, index, mapping_gfp_mask(mapping));
}
extern struct page * grab_cache_page_nowait(struct address_space *mapping,
pgoff_t index);
extern struct page * read_cache_page_async(struct address_space *mapping,
pgoff_t index, filler_t *filler,
void *data);
extern struct page * read_cache_page(struct address_space *mapping,
pgoff_t index, filler_t *filler,
void *data);
extern struct page * read_cache_page_gfp(struct address_space *mapping,
pgoff_t index, gfp_t gfp_mask);
extern int read_cache_pages(struct address_space *mapping,
struct list_head *pages, filler_t *filler, void *data);
static inline struct page *read_mapping_page_async(
struct address_space *mapping,
pgoff_t index, void *data)
{
filler_t *filler = (filler_t *)mapping->a_ops->readpage;
return read_cache_page_async(mapping, index, filler, data);
}
static inline struct page *read_mapping_page(struct address_space *mapping,
pgoff_t index, void *data)
{
filler_t *filler = (filler_t *)mapping->a_ops->readpage;
return read_cache_page(mapping, index, filler, data);
}
/*
* Return byte-offset into filesystem object for page.
*/
static inline loff_t page_offset(struct page *page)
{
return ((loff_t)page->index) << PAGE_CACHE_SHIFT;
}
extern pgoff_t linear_hugepage_index(struct vm_area_struct *vma,
unsigned long address);
static inline pgoff_t linear_page_index(struct vm_area_struct *vma,
unsigned long address)
{
pgoff_t pgoff;
if (unlikely(is_vm_hugetlb_page(vma)))
return linear_hugepage_index(vma, address);
pgoff = (address - vma->vm_start) >> PAGE_SHIFT;
pgoff += vma->vm_pgoff;
return pgoff >> (PAGE_CACHE_SHIFT - PAGE_SHIFT);
}
extern void __lock_page(struct page *page);
extern int __lock_page_killable(struct page *page);
extern void __lock_page_nosync(struct page *page);
extern int __lock_page_or_retry(struct page *page, struct mm_struct *mm,
unsigned int flags);
extern void unlock_page(struct page *page);
static inline void __set_page_locked(struct page *page)
{
__set_bit(PG_locked, &page->flags);
}
static inline void __clear_page_locked(struct page *page)
{
__clear_bit(PG_locked, &page->flags);
}
static inline int trylock_page(struct page *page)
{
return (likely(!test_and_set_bit_lock(PG_locked, &page->flags)));
}
/*
* lock_page may only be called if we have the page's inode pinned.
*/
static inline void lock_page(struct page *page)
{
might_sleep();
if (!trylock_page(page))
__lock_page(page);
}
/*
* lock_page_killable is like lock_page but can be interrupted by fatal
* signals. It returns 0 if it locked the page and -EINTR if it was
* killed while waiting.
*/
static inline int lock_page_killable(struct page *page)
{
might_sleep();
if (!trylock_page(page))
return __lock_page_killable(page);
return 0;
}
/*
* lock_page_nosync should only be used if we can't pin the page's inode.
* Doesn't play quite so well with block device plugging.
*/
static inline void lock_page_nosync(struct page *page)
{
might_sleep();
if (!trylock_page(page))
__lock_page_nosync(page);
}
/*
* lock_page_or_retry - Lock the page, unless this would block and the
* caller indicated that it can handle a retry.
*/
static inline int lock_page_or_retry(struct page *page, struct mm_struct *mm,
unsigned int flags)
{
might_sleep();
return trylock_page(page) || __lock_page_or_retry(page, mm, flags);
}
/*
* This is exported only for wait_on_page_locked/wait_on_page_writeback.
* Never use this directly!
*/
extern void wait_on_page_bit(struct page *page, int bit_nr);
/*
* Wait for a page to be unlocked.
*
* This must be called with the caller "holding" the page,
* ie with increased "page->count" so that the page won't
* go away during the wait..
*/
static inline void wait_on_page_locked(struct page *page)
{
if (PageLocked(page))
wait_on_page_bit(page, PG_locked);
}
/*
* Wait for a page to complete writeback
*/
static inline void wait_on_page_writeback(struct page *page)
{
if (PageWriteback(page))
wait_on_page_bit(page, PG_writeback);
}
extern void end_page_writeback(struct page *page);
/*
* Add an arbitrary waiter to a page's wait queue
*/
extern void add_page_wait_queue(struct page *page, wait_queue_t *waiter);
/*
* Fault a userspace page into pagetables. Return non-zero on a fault.
*
* This assumes that two userspace pages are always sufficient. That's
* not true if PAGE_CACHE_SIZE > PAGE_SIZE.
*/
static inline int fault_in_pages_writeable(char __user *uaddr, int size)
{
int ret;
if (unlikely(size == 0))
return 0;
/*
* Writing zeroes into userspace here is OK, because we know that if
* the zero gets there, we'll be overwriting it.
*/
ret = __put_user(0, uaddr);
if (ret == 0) {
char __user *end = uaddr + size - 1;
/*
* If the page was already mapped, this will get a cache miss
* for sure, so try to avoid doing it.
*/
if (((unsigned long)uaddr & PAGE_MASK) !=
((unsigned long)end & PAGE_MASK))
ret = __put_user(0, end);
}
return ret;
}
static inline int fault_in_pages_readable(const char __user *uaddr, int size)
{
volatile char c;
int ret;
if (unlikely(size == 0))
return 0;
ret = __get_user(c, uaddr);
if (ret == 0) {
const char __user *end = uaddr + size - 1;
if (((unsigned long)uaddr & PAGE_MASK) !=
((unsigned long)end & PAGE_MASK)) {
ret = __get_user(c, end);
(void)c;
}
}
return ret;
}
int add_to_page_cache_locked(struct page *page, struct address_space *mapping,
pgoff_t index, gfp_t gfp_mask);
int add_to_page_cache_lru(struct page *page, struct address_space *mapping,
pgoff_t index, gfp_t gfp_mask);
extern void remove_from_page_cache(struct page *page);
extern void __remove_from_page_cache(struct page *page);
/*
* Like add_to_page_cache_locked, but used to add newly allocated pages:
* the page is new, so we can just run __set_page_locked() against it.
*/
static inline int add_to_page_cache(struct page *page,
struct address_space *mapping, pgoff_t offset, gfp_t gfp_mask)
{
int error;
__set_page_locked(page);
error = add_to_page_cache_locked(page, mapping, offset, gfp_mask);
if (unlikely(error))
__clear_page_locked(page);
return error;
}
#endif /* _LINUX_PAGEMAP_H */