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readahead: code cleanup

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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: Jan Kara <jack@suse.cz>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: WU Fengguang <wfg@mail.ustc.edu.cn>
Signed-off-by: Fengguang Wu <wfg@mail.ustc.edu.cn>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Jan Kara
2007-05-06 14:49:26 -07:00
committed by Linus Torvalds
parent ec0f163722
commit 6ce745ed39
3 changed files with 21 additions and 20 deletions
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30
mm/readahead.c
View File

@ -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 @@ out:
* 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);