+ readahead-add-look-ahead-support-to-__do_page_cache_readahead.patch added to -mm tree

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The patch titled

     readahead: add look-ahead support to __do_page_cache_readahead()

has been added to the -mm tree.  Its filename is

     readahead-add-look-ahead-support-to-__do_page_cache_readahead.patch

See http://www.zip.com.au/~akpm/linux/patches/stuff/added-to-mm.txt to find
out what to do about this

------------------------------------------------------
Subject: readahead: add look-ahead support to __do_page_cache_readahead()
From: Wu Fengguang <wfg@xxxxxxxxxxxxxxxx>


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: Wu Fengguang <wfg@xxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxx>
---

 mm/readahead.c |   15 +++++++++------
 1 files changed, 9 insertions(+), 6 deletions(-)

diff -puN mm/readahead.c~readahead-add-look-ahead-support-to-__do_page_cache_readahead mm/readahead.c
--- 25/mm/readahead.c~readahead-add-look-ahead-support-to-__do_page_cache_readahead	Fri May 26 13:33:52 2006
+++ 25-akpm/mm/readahead.c	Fri May 26 13:33:52 2006
@@ -268,7 +268,8 @@ 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;
@@ -281,7 +282,7 @@ __do_page_cache_readahead(struct address
 	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.
@@ -304,6 +305,8 @@ __do_page_cache_readahead(struct address
 			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);
@@ -340,7 +343,7 @@ int force_page_cache_readahead(struct ad
 		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;
@@ -387,7 +390,7 @@ int do_page_cache_readahead(struct addre
 	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);
 }
 
 /*
@@ -407,7 +410,7 @@ blockable_page_cache_readahead(struct ad
 	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);
 }
@@ -452,7 +455,7 @@ static int make_ahead_window(struct addr
  * @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]()
_

Patches currently in -mm which might be from wfg@xxxxxxxxxxxxxxxx are

readahead-kconfig-options.patch
radixtree-introduce-__radix_tree_lookup_parent.patch
radixtree-introduce-radix_tree_scan_hole.patch
mm-introduce-probe_pages.patch
mm-introduce-pg_readahead.patch
readahead-add-look-ahead-support-to-__do_page_cache_readahead.patch
readahead-delay-page-release-in-do_generic_mapping_read.patch
readahead-insert-cond_resched-calls.patch
readahead-minmax_ra_pages.patch
readahead-events-accounting.patch
readahead-rescue_pages.patch
readahead-sysctl-parameters.patch
readahead-min-max-sizes.patch
readahead-state-based-method-aging-accounting.patch
readahead-state-based-method-routines.patch
readahead-state-based-method.patch
readahead-context-based-method.patch
readahead-initial-method-guiding-sizes.patch
readahead-initial-method-thrashing-guard-size.patch
readahead-initial-method-expected-read-size.patch
readahead-initial-method-user-recommended-size.patch
readahead-initial-method.patch
readahead-backward-prefetching-method.patch
readahead-seeking-reads-method.patch
readahead-thrashing-recovery-method.patch
readahead-call-scheme.patch
readahead-laptop-mode.patch
readahead-loop-case.patch
readahead-nfsd-case.patch
readahead-turn-on-by-default.patch
readahead-debug-radix-tree-new-functions.patch
readahead-debug-traces-showing-accessed-file-names.patch
readahead-debug-traces-showing-read-patterns.patch

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