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Commit 6ce745ed authored by Jan Kara's avatar Jan Kara Committed by Linus Torvalds
Browse files

readahead: code cleanup 



Rename file_ra_state.prev_page to prev_index and file_ra_state.offset to
prev_offset.  Also update of prev_index in do_generic_mapping_read() is now
moved close to the update of prev_offset.

[wfg@mail.ustc.edu.cn: fix it]
Signed-off-by: default avatarJan Kara <jack@suse.cz>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: WU Fengguang <wfg@mail.ustc.edu.cn>
Signed-off-by: default avatarFengguang Wu <wfg@mail.ustc.edu.cn>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent ec0f1637

include/linux/fs.h

+2 −2
Original line number Diff line number Diff line
@@ -696,13 +696,13 @@ struct file_ra_state { 
	unsigned long size;

	unsigned long flags;		/* ra flags RA_FLAG_xxx*/

	unsigned long cache_hit;	/* cache hit count*/

	unsigned long prev_page;	/* Cache last read() position */

	unsigned long prev_index;	/* Cache last read() position */

	unsigned long ahead_start;	/* Ahead window */

	unsigned long ahead_size;

	unsigned long ra_pages;		/* Maximum readahead window */

	unsigned long mmap_hit;		/* Cache hit stat for mmap accesses */

	unsigned long mmap_miss;	/* Cache miss stat for mmap accesses */

	unsigned int offset;		/* Offset where last read() ended in a page */

	unsigned int prev_offset;	/* Offset where last read() ended in a page */

};

#define RA_FLAG_MISS 0x01	/* a cache miss occured against this file */

#define RA_FLAG_INCACHE 0x02	/* file is already in cache */

mm/filemap.c

+4 −3
Original line number Diff line number Diff line
@@ -877,8 +877,8 @@ void do_generic_mapping_read(struct address_space *mapping, 
	cached_page = NULL;

	index = *ppos >> PAGE_CACHE_SHIFT;

	next_index = index;

	prev_index = ra.prev_page;

	prev_offset = ra.offset;

	prev_index = ra.prev_index;

	prev_offset = ra.prev_offset;

	last_index = (*ppos + desc->count + PAGE_CACHE_SIZE-1) >> PAGE_CACHE_SHIFT;

	offset = *ppos & ~PAGE_CACHE_MASK;
@@ -947,7 +947,8 @@ void do_generic_mapping_read(struct address_space *mapping, 
		offset += ret;

		index += offset >> PAGE_CACHE_SHIFT;

		offset &= ~PAGE_CACHE_MASK;

		prev_offset = ra.offset = offset;

		prev_offset = offset;

		ra.prev_offset = offset;



		page_cache_release(page);

		if (ret == nr && desc->count)

mm/readahead.c

+15 −15
Original line number Diff line number Diff line
@@ -37,7 +37,7 @@ void 
file_ra_state_init(struct file_ra_state *ra, struct address_space *mapping)

{

	ra->ra_pages = mapping->backing_dev_info->ra_pages;

	ra->prev_page = -1;

	ra->prev_index = -1;

}

EXPORT_SYMBOL_GPL(file_ra_state_init);
@@ -202,19 +202,19 @@ static int read_pages(struct address_space *mapping, struct file *filp, 
 * size:	Number of pages in that read

 *              Together, these form the "current window".

 *              Together, start and size represent the `readahead window'.

 * prev_page:   The page which the readahead algorithm most-recently inspected.

 * prev_index:  The page which the readahead algorithm most-recently inspected.

 *              It is mainly used to detect sequential file reading.

 *              If page_cache_readahead sees that it is again being called for

 *              a page which it just looked at, it can return immediately without

 *              making any state changes.

 * offset:      Offset in the prev_page where the last read ended - used for

 * offset:      Offset in the prev_index where the last read ended - used for

 *              detection of sequential file reading.

 * ahead_start,

 * ahead_size:  Together, these form the "ahead window".

 * ra_pages:	The externally controlled max readahead for this fd.

 *

 * When readahead is in the off state (size == 0), readahead is disabled.

 * In this state, prev_page is used to detect the resumption of sequential I/O.

 * In this state, prev_index is used to detect the resumption of sequential I/O.

 *

 * The readahead code manages two windows - the "current" and the "ahead"

 * windows.  The intent is that while the application is walking the pages
@@ -417,7 +417,7 @@ static int make_ahead_window(struct address_space *mapping, struct file *filp, 
	ra->ahead_size = get_next_ra_size(ra);

	ra->ahead_start = ra->start + ra->size;



	block = force || (ra->prev_page >= ra->ahead_start);

	block = force || (ra->prev_index >= ra->ahead_start);

	ret = blockable_page_cache_readahead(mapping, filp,

			ra->ahead_start, ra->ahead_size, ra, block);
@@ -469,13 +469,13 @@ page_cache_readahead(struct address_space *mapping, struct file_ra_state *ra, 
	 * We avoid doing extra work and bogusly perturbing the readahead

	 * window expansion logic.

	 */

	if (offset == ra->prev_page && --req_size)

	if (offset == ra->prev_index && --req_size)

		++offset;



	/* Note that prev_page == -1 if it is a first read */

	sequential = (offset == ra->prev_page + 1);

	ra->prev_page = offset;

	ra->offset = 0;

	/* Note that prev_index == -1 if it is a first read */

	sequential = (offset == ra->prev_index + 1);

	ra->prev_index = offset;

	ra->prev_offset = 0;



	max = get_max_readahead(ra);

	newsize = min(req_size, max);
@@ -484,7 +484,7 @@ page_cache_readahead(struct address_space *mapping, struct file_ra_state *ra, 
	if (newsize == 0 || (ra->flags & RA_FLAG_INCACHE))

		goto out;



	ra->prev_page += newsize - 1;

	ra->prev_index += newsize - 1;



	/*

	 * Special case - first read at start of file. We'll assume it's
@@ -540,18 +540,18 @@ page_cache_readahead(struct address_space *mapping, struct file_ra_state *ra, 
	 * we get called back on the first page of the ahead window which

	 * will allow us to submit more IO.

	 */

	if (ra->prev_page >= ra->ahead_start) {

	if (ra->prev_index >= ra->ahead_start) {

		ra->start = ra->ahead_start;

		ra->size = ra->ahead_size;

		make_ahead_window(mapping, filp, ra, 0);

recheck:

		/* prev_page shouldn't overrun the ahead window */

		ra->prev_page = min(ra->prev_page,

		/* prev_index shouldn't overrun the ahead window */

		ra->prev_index = min(ra->prev_index,

			ra->ahead_start + ra->ahead_size - 1);

	}



out:

	return ra->prev_page + 1;

	return ra->prev_index + 1;

}

EXPORT_SYMBOL_GPL(page_cache_readahead);