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readahead: MIN_RA_PAGES/MAX_RA_PAGES macros 

Define two convenient macros for read-ahead:
	- MAX_RA_PAGES: rounded down counterpart of VM_MAX_READAHEAD
	- MIN_RA_PAGES: rounded _up_ counterpart of VM_MIN_READAHEAD

Note that the rounded up MIN_RA_PAGES will work flawlessly with _large_
page sizes like 64k.

Signed-off-by: Fengguang Wu <wfg@mail.ustc.edu.cn>
Cc: Steven Pratt <slpratt@austin.ibm.com>
Cc: Ram Pai <linuxram@us.ibm.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Fengguang Wu 2007-07-19 01:47:58 -07:00 committed by Linus Torvalds
parent 46fc3e7b4e
commit f615bfca46
1 changed files with 10 additions and 2 deletions
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12
mm/readahead.c
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@ -21,8 +21,16 @@ void default_unplug_io_fn(struct backing_dev_info *bdi, struct page *page)
}
EXPORT_SYMBOL(default_unplug_io_fn);
/*
* Convienent macros for min/max read-ahead pages.
* Note that MAX_RA_PAGES is rounded down, while MIN_RA_PAGES is rounded up.
* The latter is necessary for systems with large page size(i.e. 64k).
*/
#define MAX_RA_PAGES (VM_MAX_READAHEAD*1024 / PAGE_CACHE_SIZE)
#define MIN_RA_PAGES DIV_ROUND_UP(VM_MIN_READAHEAD*1024, PAGE_CACHE_SIZE)
struct backing_dev_info default_backing_dev_info = {
.ra_pages = (VM_MAX_READAHEAD * 1024) / PAGE_CACHE_SIZE,
.ra_pages = MAX_RA_PAGES,
.state = 0,
.capabilities = BDI_CAP_MAP_COPY,
.unplug_io_fn = default_unplug_io_fn,
@ -51,7 +59,7 @@ static inline unsigned long get_max_readahead(struct file_ra_state *ra)
static inline unsigned long get_min_readahead(struct file_ra_state *ra)
{
return (VM_MIN_READAHEAD * 1024) / PAGE_CACHE_SIZE;
return MIN_RA_PAGES;
}
static inline void reset_ahead_window(struct file_ra_state *ra)