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readahead: combine file_ra_state.prev_index/prev_offset into prev_pos 

Combine the file_ra_state members
				unsigned long prev_index
				unsigned int prev_offset
into
				loff_t prev_pos

It is more consistent and better supports huge files.

Thanks to Peter for the nice proposal!

[akpm@linux-foundation.org: fix shift overflow]
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Fengguang Wu <wfg@mail.ustc.edu.cn>
Cc: Rusty Russell <rusty@rustcorp.com.au>
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 2007-10-16 01:24:33 -07:00 committed by Linus Torvalds
parent 0bb7ba6b9c
commit f4e6b498d6
6 changed files with 19 additions and 18 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
fs/ext3/dir.c
View File

@ -143,7 +143,7 @@ static int ext3_readdir(struct file * filp,
sb->s_bdev->bd_inode->i_mapping,
&filp->f_ra, filp,
index, 1);
filp->f_ra.prev_index = index;
filp->f_ra.prev_pos = (loff_t)index << PAGE_CACHE_SHIFT;
bh = ext3_bread(NULL, inode, blk, 0, &err);
}

2
fs/ext4/dir.c
View File

@ -142,7 +142,7 @@ static int ext4_readdir(struct file * filp,
sb->s_bdev->bd_inode->i_mapping,
&filp->f_ra, filp,
index, 1);
filp->f_ra.prev_index = index;
filp->f_ra.prev_pos = (loff_t)index << PAGE_CACHE_SHIFT;
bh = ext4_bread(NULL, inode, blk, 0, &err);
}

2
fs/splice.c
View File

@ -447,7 +447,7 @@ fill_it:
*/
while (page_nr < nr_pages)
page_cache_release(pages[page_nr++]);
in->f_ra.prev_index = index;
in->f_ra.prev_pos = (loff_t)index << PAGE_CACHE_SHIFT;
if (spd.nr_pages)
return splice_to_pipe(pipe, &spd);

3
include/linux/fs.h
View File

@ -704,8 +704,7 @@ struct file_ra_state {
unsigned int ra_pages; /* Maximum readahead window */
int mmap_miss; /* Cache miss stat for mmap accesses */
unsigned long prev_index; /* Cache last read() position */
unsigned int prev_offset; /* Offset where last read() ended in a page */
loff_t prev_pos; /* Cache last read() position */
};
/*

13
mm/filemap.c
View File

@ -879,8 +879,8 @@ void do_generic_mapping_read(struct address_space *mapping,
cached_page = NULL;
index = *ppos >> PAGE_CACHE_SHIFT;
next_index = index;
prev_index = ra.prev_index;
prev_offset = ra.prev_offset;
prev_index = ra.prev_pos >> PAGE_CACHE_SHIFT;
prev_offset = ra.prev_pos & (PAGE_CACHE_SIZE-1);
last_index = (*ppos + desc->count + PAGE_CACHE_SIZE-1) >> PAGE_CACHE_SHIFT;
offset = *ppos & ~PAGE_CACHE_MASK;
@ -966,7 +966,6 @@ page_ok:
index += offset >> PAGE_CACHE_SHIFT;
offset &= ~PAGE_CACHE_MASK;
prev_offset = offset;
ra.prev_offset = offset;
page_cache_release(page);
if (ret == nr && desc->count)
@ -1056,9 +1055,11 @@ no_cached_page:
out:
*_ra = ra;
_ra->prev_index = prev_index;
_ra->prev_pos = prev_index;
_ra->prev_pos <<= PAGE_CACHE_SHIFT;
_ra->prev_pos |= prev_offset;
*ppos = ((loff_t) index << PAGE_CACHE_SHIFT) + offset;
*ppos = ((loff_t)index << PAGE_CACHE_SHIFT) + offset;
if (cached_page)
page_cache_release(cached_page);
if (filp)
@ -1396,7 +1397,7 @@ retry_find:
* Found the page and have a reference on it.
*/
mark_page_accessed(page);
ra->prev_index = page->index;
ra->prev_pos = (loff_t)page->index << PAGE_CACHE_SHIFT;
vmf->page = page;
return ret | VM_FAULT_LOCKED;

13
mm/readahead.c
View File

@ -46,7 +46,7 @@ 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_index = -1;
ra->prev_pos = -1;
}
EXPORT_SYMBOL_GPL(file_ra_state_init);
@ -327,7 +327,7 @@ static unsigned long get_next_ra_size(struct file_ra_state *ra,
* indicator. The flag won't be set on already cached pages, to avoid the
* readahead-for-nothing fuss, saving pointless page cache lookups.
*
* prev_index tracks the last visited page in the _previous_ read request.
* prev_pos tracks the last visited byte in the _previous_ read request.
* It should be maintained by the caller, and will be used for detecting
* small random reads. Note that the readahead algorithm checks loosely
* for sequential patterns. Hence interleaved reads might be served as
@ -351,12 +351,10 @@ ondemand_readahead(struct address_space *mapping,
bool hit_readahead_marker, pgoff_t offset,
unsigned long req_size)
{
int max; /* max readahead pages */
int max = ra->ra_pages; /* max readahead pages */
pgoff_t prev_offset;
int sequential;
max = ra->ra_pages;
sequential = (offset - ra->prev_index <= 1UL) || (req_size > max);
/*
* It's the expected callback offset, assume sequential access.
* Ramp up sizes, and push forward the readahead window.
@ -369,6 +367,9 @@ ondemand_readahead(struct address_space *mapping,
goto readit;
}
prev_offset = ra->prev_pos >> PAGE_CACHE_SHIFT;
sequential = offset - prev_offset <= 1UL || req_size > max;
/*
* Standalone, small read.
* Read as is, and do not pollute the readahead state.