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[PATCH] readahead commentary

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Add a few comments surrounding the generic readahead API.

Also convert some ulongs into pgoff_t: the identifier for PAGE_CACHE_SIZE
offsets into pagecache.

Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Andrew Morton 2005-11-07 00:59:28 -08:00 committed by Linus Torvalds
parent bf8f972d3a
commit 7361f4d8ca
2 changed files with 26 additions and 13 deletions
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8
include/linux/mm.h
View File

@ -932,13 +932,13 @@ int write_one_page(struct page *page, int wait);
* turning readahead off */ * turning readahead off */
int do_page_cache_readahead(struct address_space *mapping, struct file *filp, int do_page_cache_readahead(struct address_space *mapping, struct file *filp,
unsigned long offset, unsigned long nr_to_read); pgoff_t offset, unsigned long nr_to_read);
int force_page_cache_readahead(struct address_space *mapping, struct file *filp, int force_page_cache_readahead(struct address_space *mapping, struct file *filp,
unsigned long offset, unsigned long nr_to_read); pgoff_t offset, unsigned long nr_to_read);
unsigned long page_cache_readahead(struct address_space *mapping, unsigned long page_cache_readahead(struct address_space *mapping,
struct file_ra_state *ra, struct file_ra_state *ra,
struct file *filp, struct file *filp,
unsigned long offset, pgoff_t offset,
unsigned long size); unsigned long size);
void handle_ra_miss(struct address_space *mapping, void handle_ra_miss(struct address_space *mapping,
struct file_ra_state *ra, pgoff_t offset); struct file_ra_state *ra, pgoff_t offset);

31
mm/readahead.c
View File

@ -254,7 +254,7 @@ out:
*/ */
static int static int
__do_page_cache_readahead(struct address_space *mapping, struct file *filp, __do_page_cache_readahead(struct address_space *mapping, struct file *filp,
unsigned long offset, unsigned long nr_to_read) pgoff_t offset, unsigned long nr_to_read)
{ {
struct inode *inode = mapping->host; struct inode *inode = mapping->host;
struct page *page; struct page *page;
@ -274,7 +274,7 @@ __do_page_cache_readahead(struct address_space *mapping, struct file *filp,
*/ */
read_lock_irq(&mapping->tree_lock); read_lock_irq(&mapping->tree_lock);
for (page_idx = 0; page_idx < nr_to_read; page_idx++) { for (page_idx = 0; page_idx < nr_to_read; page_idx++) {
unsigned long page_offset = offset + page_idx; pgoff_t page_offset = offset + page_idx;
if (page_offset > end_index) if (page_offset > end_index)
break; break;
@ -311,7 +311,7 @@ out:
* memory at once. * memory at once.
*/ */
int force_page_cache_readahead(struct address_space *mapping, struct file *filp, int force_page_cache_readahead(struct address_space *mapping, struct file *filp,
unsigned long offset, unsigned long nr_to_read) pgoff_t offset, unsigned long nr_to_read)
{ {
int ret = 0; int ret = 0;
@ -368,7 +368,7 @@ static inline int check_ra_success(struct file_ra_state *ra,
* request queues. * request queues.
*/ */
int do_page_cache_readahead(struct address_space *mapping, struct file *filp, int do_page_cache_readahead(struct address_space *mapping, struct file *filp,
unsigned long offset, unsigned long nr_to_read) pgoff_t offset, unsigned long nr_to_read)
{ {
if (bdi_read_congested(mapping->backing_dev_info)) if (bdi_read_congested(mapping->backing_dev_info))
return -1; return -1;
@ -385,7 +385,7 @@ int do_page_cache_readahead(struct address_space *mapping, struct file *filp,
*/ */
static int static int
blockable_page_cache_readahead(struct address_space *mapping, struct file *filp, blockable_page_cache_readahead(struct address_space *mapping, struct file *filp,
unsigned long offset, unsigned long nr_to_read, pgoff_t offset, unsigned long nr_to_read,
struct file_ra_state *ra, int block) struct file_ra_state *ra, int block)
{ {
int actual; int actual;
@ -430,14 +430,27 @@ static int make_ahead_window(struct address_space *mapping, struct file *filp,
return ret; return ret;
} }
/* /**
* page_cache_readahead is the main function. If performs the adaptive * page_cache_readahead - generic adaptive readahead
* @mapping: address_space which holds the pagecache and I/O vectors
* @ra: file_ra_state which holds the readahead state
* @filp: passed on to ->readpage() and ->readpages()
* @offset: start offset into @mapping, in PAGE_CACHE_SIZE units
* @req_size: hint: total size of the read which the caller is performing in
* PAGE_CACHE_SIZE units
*
* page_cache_readahead() is the main function. If performs the adaptive
* readahead window size management and submits the readahead I/O. * readahead window size management and submits the readahead I/O.
*
* Note that @filp is purely used for passing on to the ->readpage[s]()
* handler: it may refer to a different file from @mapping (so we may not use
* @filp->f_mapping or @filp->f_dentry->d_inode here).
* Also, @ra may not be equal to &@filp->f_ra.
*
*/ */
unsigned long unsigned long
page_cache_readahead(struct address_space *mapping, struct file_ra_state *ra, page_cache_readahead(struct address_space *mapping, struct file_ra_state *ra,
struct file *filp, unsigned long offset, struct file *filp, pgoff_t offset, unsigned long req_size)
unsigned long req_size)
{ {
unsigned long max, newsize; unsigned long max, newsize;
int sequential; int sequential;