aboutsummaryrefslogtreecommitdiffstats
diff options
context:
space:
mode:
authorFengguang Wu <wfg@mail.ustc.edu.cn>2007-07-19 04:47:57 -0400
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2007-07-19 13:04:43 -0400
commit46fc3e7b4e7233a0ac981ac9084b55217318d04d (patch)
tree555bededb43671605fa085d3b4d330d31aa4af5c
parentd77c2d7cc5126639a47d73300b40d461f2811a0f (diff)
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>
-rw-r--r--mm/readahead.c15
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:
265 */ 265 */
266static int 266static int
267__do_page_cache_readahead(struct address_space *mapping, struct file *filp, 267__do_page_cache_readahead(struct address_space *mapping, struct file *filp,
268 pgoff_t offset, unsigned long nr_to_read) 268 pgoff_t offset, unsigned long nr_to_read,
269 unsigned long lookahead_size)
269{ 270{
270 struct inode *inode = mapping->host; 271 struct inode *inode = mapping->host;
271 struct page *page; 272 struct page *page;
@@ -278,7 +279,7 @@ __do_page_cache_readahead(struct address_space *mapping, struct file *filp,
278 if (isize == 0) 279 if (isize == 0)
279 goto out; 280 goto out;
280 281
281 end_index = ((isize - 1) >> PAGE_CACHE_SHIFT); 282 end_index = ((isize - 1) >> PAGE_CACHE_SHIFT);
282 283
283 /* 284 /*
284 * Preallocate as many pages as we will need. 285 * Preallocate as many pages as we will need.
@@ -301,6 +302,8 @@ __do_page_cache_readahead(struct address_space *mapping, struct file *filp,
301 break; 302 break;
302 page->index = page_offset; 303 page->index = page_offset;
303 list_add(&page->lru, &page_pool); 304 list_add(&page->lru, &page_pool);
305 if (page_idx == nr_to_read - lookahead_size)
306 SetPageReadahead(page);
304 ret++; 307 ret++;
305 } 308 }
306 read_unlock_irq(&mapping->tree_lock); 309 read_unlock_irq(&mapping->tree_lock);
@@ -337,7 +340,7 @@ int force_page_cache_readahead(struct address_space *mapping, struct file *filp,
337 if (this_chunk > nr_to_read) 340 if (this_chunk > nr_to_read)
338 this_chunk = nr_to_read; 341 this_chunk = nr_to_read;
339 err = __do_page_cache_readahead(mapping, filp, 342 err = __do_page_cache_readahead(mapping, filp,
340 offset, this_chunk); 343 offset, this_chunk, 0);
341 if (err < 0) { 344 if (err < 0) {
342 ret = err; 345 ret = err;
343 break; 346 break;
@@ -384,7 +387,7 @@ int do_page_cache_readahead(struct address_space *mapping, struct file *filp,
384 if (bdi_read_congested(mapping->backing_dev_info)) 387 if (bdi_read_congested(mapping->backing_dev_info))
385 return -1; 388 return -1;
386 389
387 return __do_page_cache_readahead(mapping, filp, offset, nr_to_read); 390 return __do_page_cache_readahead(mapping, filp, offset, nr_to_read, 0);
388} 391}
389 392
390/* 393/*
@@ -404,7 +407,7 @@ blockable_page_cache_readahead(struct address_space *mapping, struct file *filp,
404 if (!block && bdi_read_congested(mapping->backing_dev_info)) 407 if (!block && bdi_read_congested(mapping->backing_dev_info))
405 return 0; 408 return 0;
406 409
407 actual = __do_page_cache_readahead(mapping, filp, offset, nr_to_read); 410 actual = __do_page_cache_readahead(mapping, filp, offset, nr_to_read, 0);
408 411
409 return check_ra_success(ra, nr_to_read, actual); 412 return check_ra_success(ra, nr_to_read, actual);
410} 413}
@@ -449,7 +452,7 @@ static int make_ahead_window(struct address_space *mapping, struct file *filp,
449 * @req_size: hint: total size of the read which the caller is performing in 452 * @req_size: hint: total size of the read which the caller is performing in
450 * PAGE_CACHE_SIZE units 453 * PAGE_CACHE_SIZE units
451 * 454 *
452 * page_cache_readahead() is the main function. If performs the adaptive 455 * page_cache_readahead() is the main function. It performs the adaptive
453 * readahead window size management and submits the readahead I/O. 456 * readahead window size management and submits the readahead I/O.
454 * 457 *
455 * Note that @filp is purely used for passing on to the ->readpage[s]() 458 * Note that @filp is purely used for passing on to the ->readpage[s]()