[PATCH 2/8] readahead: make default readahead size a kernel parameter

[Wu Fengguang]

From: Nikanth Karthikesan <knikanth@xxxxxxx>

Add new kernel parameter "readahead=", which allows user to override
the static VM_MAX_READAHEAD=128kb.

CC: Ankit Jain <radical@xxxxxxxxx>
CC: Dave Chinner <david@xxxxxxxxxxxxx>
CC: Christian Ehrhardt <ehrhardt@xxxxxxxxxxxxxxxxxx>
Acked-by: Rik van Riel <riel@xxxxxxxxxx>
Signed-off-by: Nikanth Karthikesan <knikanth@xxxxxxx>
Signed-off-by: Wu Fengguang <fengguang.wu@xxxxxxxxx>
---
 Documentation/kernel-parameters.txt |    6 ++++++
 block/blk-core.c                    |    3 +--
 fs/fuse/inode.c                     |    2 +-
 mm/readahead.c                      |   19 +++++++++++++++++++
 4 files changed, 27 insertions(+), 3 deletions(-)

--- linux-next.orig/Documentation/kernel-parameters.txt	2011-10-19 11:11:14.000000000 +0800
+++ linux-next/Documentation/kernel-parameters.txt	2011-11-20 11:09:56.000000000 +0800
@@ -2245,6 +2245,12 @@ bytes respectively. Such letter suffixes
 			Run specified binary instead of /init from the ramdisk,
 			used for early userspace startup. See initrd.
 
+	readahead=nn[KM]
+			Default max readahead size for block devices.
+
+			This default max readahead size may be overrode
+			in some cases, notably NFS, btrfs and software RAID.
+
 	reboot=		[BUGS=X86-32,BUGS=ARM,BUGS=IA-64] Rebooting mode
 			Format: <reboot_mode>[,<reboot_mode2>[,...]]
 			See arch/*/kernel/reboot.c or arch/*/kernel/process.c
--- linux-next.orig/block/blk-core.c	2011-11-08 10:18:16.000000000 +0800
+++ linux-next/block/blk-core.c	2011-11-20 10:49:33.000000000 +0800
@@ -462,8 +462,7 @@ struct request_queue *blk_alloc_queue_no
 	if (!q)
 		return NULL;
 
-	q->backing_dev_info.ra_pages =
-			(VM_MAX_READAHEAD * 1024) / PAGE_CACHE_SIZE;
+	q->backing_dev_info.ra_pages = default_backing_dev_info.ra_pages;
 	q->backing_dev_info.state = 0;
 	q->backing_dev_info.capabilities = BDI_CAP_MAP_COPY;
 	q->backing_dev_info.name = "block";
--- linux-next.orig/fs/fuse/inode.c	2011-11-08 10:18:39.000000000 +0800
+++ linux-next/fs/fuse/inode.c	2011-11-20 10:50:12.000000000 +0800
@@ -878,7 +878,7 @@ static int fuse_bdi_init(struct fuse_con
 	int err;
 
 	fc->bdi.name = "fuse";
-	fc->bdi.ra_pages = (VM_MAX_READAHEAD * 1024) / PAGE_CACHE_SIZE;
+	fc->bdi.ra_pages = default_backing_dev_info.ra_pages;
 	/* fuse does it's own writeback accounting */
 	fc->bdi.capabilities = BDI_CAP_NO_ACCT_WB;
 
--- linux-next.orig/mm/readahead.c	2011-11-20 10:48:57.000000000 +0800
+++ linux-next/mm/readahead.c	2011-11-20 11:09:22.000000000 +0800
@@ -18,6 +18,25 @@
 #include <linux/pagevec.h>
 #include <linux/pagemap.h>
 
+static int __init config_readahead_size(char *str)
+{
+	unsigned long bytes;
+
+	if (!str)
+		return -EINVAL;
+	bytes = memparse(str, &str);
+	if (*str != '\0')
+		return -EINVAL;
+
+	/* missed 'k'/'m' suffixes? */
+	if (bytes && bytes < PAGE_CACHE_SIZE)
+		return -EINVAL;
+
+	default_backing_dev_info.ra_pages = bytes / PAGE_CACHE_SIZE;
+	return 0;
+}
+early_param("readahead", config_readahead_size);
+
 /*
  * Initialise a struct file's readahead state.  Assumes that the caller has
  * memset *ra to zero.


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