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