make default readahead size a kernel parameter

From: Nikanth Karthikesan <knikanth@suse.de>

Add new kernel parameter "readahead", which would be used instead of the
value of VM_MAX_READAHEAD. If the parameter is not specified, the default
of 128kb would be used.

Change-Id: I58540d4c3570d23befb9b9f1e27998e832eae88b
CC: Ankit Jain <radical@gmail.com>
CC: Dave Chinner <david@fromorbit.com>
CC: Christian Ehrhardt <ehrhardt@linux.vnet.ibm.com>
Signed-off-by: Nikanth Karthikesan <knikanth@suse.de>
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
Signed-off-by: D. Andrei Măceș <dmaces@nd.edu>

5 files changed, 34 insertions, 3 deletions

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 3899234..b82f69fd 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -2198,6 +2198,10 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 			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.
+			Range: 0; 4k - 128m
+
 	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
diff --git a/block/blk-core.c b/block/blk-core.c
index 35ae52d..8d881b0 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -413,8 +413,7 @@ struct request_queue *blk_alloc_queue_node(gfp_t gfp_mask, int node_id)
 	if (!q)
 		return NULL;
 
-	q->backing_dev_info.ra_pages =
-			(VM_MAX_READAHEAD * 1024) / PAGE_CACHE_SIZE;
+	q->backing_dev_info.ra_pages = max_readahead_pages;
 	q->backing_dev_info.state = 0;
 	q->backing_dev_info.capabilities = BDI_CAP_MAP_COPY;
 	q->backing_dev_info.name = "block";
diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index 69a1e0f..a32d532 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -884,7 +884,7 @@ static int fuse_bdi_init(struct fuse_conn *fc, struct super_block *sb)
 	int err;
 
 	fc->bdi.name = "fuse";
-	fc->bdi.ra_pages = (VM_MAX_READAHEAD * 1024) / PAGE_CACHE_SIZE;
+	fc->bdi.ra_pages = max_readahead_pages;
 	/* fuse does it's own writeback accounting */
 	fc->bdi.capabilities = BDI_CAP_NO_ACCT_WB;
 
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 815d809..2a3b05a 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1473,6 +1473,8 @@ void task_dirty_inc(struct task_struct *tsk);
 #define VM_MAX_READAHEAD	128	/* kbytes */
 #define VM_MIN_READAHEAD	16	/* kbytes (includes current page) */
 
+extern unsigned long max_readahead_pages;
+
 int force_page_cache_readahead(struct address_space *mapping, struct file *filp,
 			pgoff_t offset, unsigned long nr_to_read);
 
diff --git a/mm/readahead.c b/mm/readahead.c
index 867f9dd..df60df9 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -18,6 +18,32 @@
 #include <linux/pagevec.h>
 #include <linux/pagemap.h>
 
+unsigned long max_readahead_pages = VM_MAX_READAHEAD * 1024 / PAGE_CACHE_SIZE;
+
+static int __init readahead(char *str)
+{
+	unsigned long bytes;
+
+	if (!str)
+		return -EINVAL;
+	bytes = memparse(str, &str);
+	if (*str != '\0')
+		return -EINVAL;
+
+	if (bytes) {
+		if (bytes < PAGE_CACHE_SIZE)	/* missed 'k'/'m' suffixes? */
+			return -EINVAL;
+		if (bytes > 128 << 20)		/* limit to 128MB */
+			bytes = 128 << 20;
+	}
+
+	max_readahead_pages = bytes / PAGE_CACHE_SIZE;
+	default_backing_dev_info.ra_pages = max_readahead_pages;
+	return 0;
+}
+
+early_param("readahead", readahead);
+
 /*
  * Initialise a struct file's readahead state.  Assumes that the caller has
  * memset *ra to zero.