[PATCH 16/28] readahead: initial method - guiding sizes

[Wu Fengguang <wfg@mail.ustc.edu.cn>]

Introduce three guiding sizes for the initial readahead method.
	- ra_pages0:	   min readahead on start-of-file
	- ra_thrash_bytes: estimated thrashing threshold

ra_thrash_bytes defaults to large value:
	- most systems don't have the danger of thrashing
	- it increases slowly and drops rapidly

Signed-off-by: Wu Fengguang <wfg@mail.ustc.edu.cn>
Signed-off-by: Andrew Morton <akpm@osdl.org>
--- linux-2.6.19-rc5-mm2.orig/include/linux/backing-dev.h
+++ linux-2.6.19-rc5-mm2/include/linux/backing-dev.h
@@ -26,6 +26,8 @@ typedef int (congested_fn)(void *, int);
 
 struct backing_dev_info {
 	unsigned long ra_pages;	/* max readahead in PAGE_CACHE_SIZE units */
+	unsigned long ra_pages0; /* min readahead on start of file */
+	unsigned long ra_thrash_bytes;	/* estimated thrashing threshold */
 	unsigned long state;	/* Always use atomic bitops on this */
 	unsigned int capabilities; /* Device capabilities */
 	congested_fn *congested_fn; /* Function pointer if device is md/dm */
--- linux-2.6.19-rc5-mm2.orig/mm/readahead.c
+++ linux-2.6.19-rc5-mm2/mm/readahead.c
@@ -32,6 +32,9 @@
  * Adaptive read-ahead parameters.
  */
 
+/* Default initial read-ahead size. */
+#define INITIAL_RA_PAGES  DIV_ROUND_UP(64*1024, PAGE_CACHE_SIZE)
+
 /* In laptop mode, poll delayed look-ahead on every ## pages read. */
 #define LAPTOP_POLL_INTERVAL 16
 
@@ -114,6 +117,8 @@ EXPORT_SYMBOL(default_unplug_io_fn);
 
 struct backing_dev_info default_backing_dev_info = {
 	.ra_pages	= MAX_RA_PAGES,
+	.ra_pages0	= INITIAL_RA_PAGES,
+	.ra_thrash_bytes = MAX_RA_PAGES * PAGE_CACHE_SIZE,
 	.state		= 0,
 	.capabilities	= BDI_CAP_MAP_COPY,
 	.unplug_io_fn	= default_unplug_io_fn,
--- linux-2.6.19-rc5-mm2.orig/block/ll_rw_blk.c
+++ linux-2.6.19-rc5-mm2/block/ll_rw_blk.c
@@ -214,9 +214,6 @@ void blk_queue_make_request(request_queu
 	blk_queue_max_phys_segments(q, MAX_PHYS_SEGMENTS);
 	blk_queue_max_hw_segments(q, MAX_HW_SEGMENTS);
 	q->make_request_fn = mfn;
-	q->backing_dev_info.ra_pages = (VM_MAX_READAHEAD * 1024) / PAGE_CACHE_SIZE;
-	q->backing_dev_info.state = 0;
-	q->backing_dev_info.capabilities = BDI_CAP_MAP_COPY;
 	blk_queue_max_sectors(q, SAFE_MAX_SECTORS);
 	blk_queue_hardsect_size(q, 512);
 	blk_queue_dma_alignment(q, 511);
@@ -1848,6 +1845,7 @@ request_queue_t *blk_alloc_queue_node(gf
 	q->kobj.ktype = &queue_ktype;
 	kobject_init(&q->kobj);
 
+	q->backing_dev_info = default_backing_dev_info;
 	q->backing_dev_info.unplug_io_fn = blk_backing_dev_unplug;
 	q->backing_dev_info.unplug_io_data = q;
 

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