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| author | Fengguang Wu <wfg@mail.ustc.edu.cn> | 2007-07-19 01:47:57 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@woody.linux-foundation.org> | 2007-07-19 10:04:43 -0700 |
| commit | 46fc3e7b4e7233a0ac981ac9084b55217318d04d (patch) | |
| tree | 555bededb43671605fa085d3b4d330d31aa4af5c /mm/readahead.c | |
| parent | d77c2d7cc5126639a47d73300b40d461f2811a0f (diff) | |
| download | lwn-46fc3e7b4e7233a0ac981ac9084b55217318d04d.tar.gz lwn-46fc3e7b4e7233a0ac981ac9084b55217318d04d.zip | |
readahead: add look-ahead support to __do_page_cache_readahead()
Add look-ahead support to __do_page_cache_readahead().
It works by
- mark the Nth backwards page with PG_readahead,
(which instructs the page's first reader to invoke readahead)
- and only do the marking for newly allocated pages.
(to prevent blindly doing readahead on already cached pages)
Look-ahead is a technique to achieve I/O pipelining:
While the application is working through a chunk of cached pages, the kernel
reads-ahead the next chunk of pages _before_ time of need. It effectively
hides low level I/O latencies to high level applications.
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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/readahead.c')
| -rw-r--r-- | mm/readahead.c | 15 |
1 files changed, 9 insertions, 6 deletions
diff --git a/mm/readahead.c b/mm/readahead.c index 9861e883fe57..88ea0f29aac8 100644 --- a/mm/readahead.c +++ b/mm/readahead.c @@ -265,7 +265,8 @@ out: */ static int __do_page_cache_readahead(struct address_space *mapping, struct file *filp, - pgoff_t offset, unsigned long nr_to_read) + pgoff_t offset, unsigned long nr_to_read, + unsigned long lookahead_size) { struct inode *inode = mapping->host; struct page *page; @@ -278,7 +279,7 @@ __do_page_cache_readahead(struct address_space *mapping, struct file *filp, if (isize == 0) goto out; - end_index = ((isize - 1) >> PAGE_CACHE_SHIFT); + end_index = ((isize - 1) >> PAGE_CACHE_SHIFT); /* * Preallocate as many pages as we will need. @@ -301,6 +302,8 @@ __do_page_cache_readahead(struct address_space *mapping, struct file *filp, break; page->index = page_offset; list_add(&page->lru, &page_pool); + if (page_idx == nr_to_read - lookahead_size) + SetPageReadahead(page); ret++; } read_unlock_irq(&mapping->tree_lock); @@ -337,7 +340,7 @@ int force_page_cache_readahead(struct address_space *mapping, struct file *filp, if (this_chunk > nr_to_read) this_chunk = nr_to_read; err = __do_page_cache_readahead(mapping, filp, - offset, this_chunk); + offset, this_chunk, 0); if (err < 0) { ret = err; break; @@ -384,7 +387,7 @@ int do_page_cache_readahead(struct address_space *mapping, struct file *filp, if (bdi_read_congested(mapping->backing_dev_info)) return -1; - return __do_page_cache_readahead(mapping, filp, offset, nr_to_read); + return __do_page_cache_readahead(mapping, filp, offset, nr_to_read, 0); } /* @@ -404,7 +407,7 @@ blockable_page_cache_readahead(struct address_space *mapping, struct file *filp, if (!block && bdi_read_congested(mapping->backing_dev_info)) return 0; - actual = __do_page_cache_readahead(mapping, filp, offset, nr_to_read); + actual = __do_page_cache_readahead(mapping, filp, offset, nr_to_read, 0); return check_ra_success(ra, nr_to_read, actual); } @@ -449,7 +452,7 @@ static int make_ahead_window(struct address_space *mapping, struct file *filp, * @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 + * page_cache_readahead() is the main function. It performs the adaptive * readahead window size management and submits the readahead I/O. * * Note that @filp is purely used for passing on to the ->readpage[s]() |