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From: Ankit Jain on 11 Feb 2010 06:20
> +static int __init readahead(char *str)
> +{
> + � � � if (!str)
> + � � � � � � � return -EINVAL;
> + � � � vm_max_readahead_kb = memparse(str, &str) / 1024ULL;

Just wondering, shouldn't you check whether the str had a valid value
[memparse (str, &next); next > str ..] and if it didn't, then use the
DEFAULT_VM_MAX_READAHEAD ? Otherwise, incase of a invalid
value, the readahead value will become zero.

> + � � � default_backing_dev_info.ra_pages = vm_max_readahead_kb
> + � � � � � � � � � � � � � � � � � � � � � � � * 1024 / PAGE_CACHE_SIZE;
> + � � � return 0;
> +}
> +
> +early_param("readahead", readahead);
> +

-Ankit
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From: Nikanth Karthikesan on 11 Feb 2010 06:50
On Thursday 11 February 2010 16:45:24 Ankit Jain wrote:
> > +static int __init readahead(char *str)
> > +{
> > + if (!str)
> > + return -EINVAL;
> > + vm_max_readahead_kb = memparse(str, &str) / 1024ULL;
>
> Just wondering, shouldn't you check whether the str had a valid value
> [memparse (str, &next); next > str ..] and if it didn't, then use the
> DEFAULT_VM_MAX_READAHEAD ? Otherwise, incase of a invalid
> value, the readahead value will become zero.
>

Thanks for the review. Here is the fixed patch that checks whether all of the
parameters value is consumed.

Thanks
Nikanth

From: Nikanth Karthikesan <knikanth(a)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.

Signed-off-by: Nikanth Karthikesan <knikanth(a)suse.de>

---

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 736d456..354e6f1 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -2148,6 +2148,8 @@ and is between 256 and 4096 characters. It is defined in the file
Format: <reboot_mode>[,<reboot_mode2>[,...]]
See arch/*/kernel/reboot.c or arch/*/kernel/process.c

+ readahead= Default readahead value for block devices.
+
relax_domain_level=
[KNL, SMP] Set scheduler's default relax_domain_level.
See Documentation/cgroups/cpusets.txt.
diff --git a/block/blk-core.c b/block/blk-core.c
index 718897e..02ed748 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -499,7 +499,7 @@ struct request_queue *blk_alloc_queue_node(gfp_t gfp_mask, int node_id)
q->backing_dev_info.unplug_io_fn = blk_backing_dev_unplug;
q->backing_dev_info.unplug_io_data = q;
q->backing_dev_info.ra_pages =
- (VM_MAX_READAHEAD * 1024) / PAGE_CACHE_SIZE;
+ (vm_max_readahead_kb * 1024) / PAGE_CACHE_SIZE;
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 1a822ce..a593578 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -870,7 +870,7 @@ 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 = (vm_max_readahead_kb * 1024) / PAGE_CACHE_SIZE;
fc->bdi.unplug_io_fn = default_unplug_io_fn;
/* 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 60c467b..17825d7 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1188,9 +1188,11 @@ int write_one_page(struct page *page, int wait);
void task_dirty_inc(struct task_struct *tsk);

/* readahead.c */
-#define VM_MAX_READAHEAD 128 /* kbytes */
+#define DEFAULT_VM_MAX_READAHEAD 128 /* kbytes */
#define VM_MIN_READAHEAD 16 /* kbytes (includes current page) */

+extern unsigned long vm_max_readahead_kb;
+
int force_page_cache_readahead(struct address_space *mapping, struct file *filp,
pgoff_t offset, unsigned long nr_to_read);

diff --git a/init/main.c b/init/main.c
index 4cb47a1..6c451d2 100644
--- a/init/main.c
+++ b/init/main.c
@@ -70,6 +70,7 @@
#include <linux/sfi.h>
#include <linux/shmem_fs.h>
#include <trace/boot.h>
+#include <linux/backing-dev.h>

#include <asm/io.h>
#include <asm/bugs.h>
@@ -249,6 +250,24 @@ static int __init loglevel(char *str)

early_param("loglevel", loglevel);

+static int __init readahead(char *str)
+{
+ unsigned long readahead_kb;
+
+ if (!str)
+ return -EINVAL;
+ readahead_kb = memparse(str, &str) / 1024ULL;
+ if (*str != '\0')
+ return -EINVAL;
+
+ vm_max_readahead_kb = readahead_kb;
+ default_backing_dev_info.ra_pages = vm_max_readahead_kb
+ * 1024 / PAGE_CACHE_SIZE;
+ return 0;
+}
+
+early_param("readahead", readahead);
+
/*
* Unknown boot options get handed to init, unless they look like
* unused parameters (modprobe will find them in /proc/cmdline).
diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index 0e8ca03..e33ff34 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -18,7 +18,7 @@ EXPORT_SYMBOL(default_unplug_io_fn);

struct backing_dev_info default_backing_dev_info = {
.name = "default",
- .ra_pages = VM_MAX_READAHEAD * 1024 / PAGE_CACHE_SIZE,
+ .ra_pages = DEFAULT_VM_MAX_READAHEAD * 1024 / PAGE_CACHE_SIZE,
.state = 0,
.capabilities = BDI_CAP_MAP_COPY,
.unplug_io_fn = default_unplug_io_fn,
diff --git a/mm/readahead.c b/mm/readahead.c
index 033bc13..516f8da 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -17,6 +17,8 @@
#include <linux/pagevec.h>
#include <linux/pagemap.h>

+unsigned long vm_max_readahead_kb = DEFAULT_VM_MAX_READAHEAD;
+
/*
* Initialise a struct file's readahead state. Assumes that the caller has
* memset *ra to zero.
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From: Wu Fengguang on 11 Feb 2010 10:20
Nikanth,

> From: Nikanth Karthikesan <knikanth(a)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.

The patch looks good to me, though it conflicts with my patches.
Do you mind me including a modified version in my readahead patchset?

Thanks,
Fengguang
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From: Dave Chinner on 14 Feb 2010 16:40
On Thu, Feb 11, 2010 at 05:15:03PM +0530, Nikanth Karthikesan wrote:
> On Thursday 11 February 2010 16:45:24 Ankit Jain wrote:
> > > +static int __init readahead(char *str)
> > > +{
> > > + if (!str)
> > > + return -EINVAL;
> > > + vm_max_readahead_kb = memparse(str, &str) / 1024ULL;
> >
> > Just wondering, shouldn't you check whether the str had a valid value
> > [memparse (str, &next); next > str ..] and if it didn't, then use the
> > DEFAULT_VM_MAX_READAHEAD ? Otherwise, incase of a invalid
> > value, the readahead value will become zero.
> >
>
> Thanks for the review. Here is the fixed patch that checks whether all of the
> parameters value is consumed.
>
> Thanks
> Nikanth
>
> From: Nikanth Karthikesan <knikanth(a)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.
>
> Signed-off-by: Nikanth Karthikesan <knikanth(a)suse.de>
>
> ---
>
> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
> index 736d456..354e6f1 100644
> --- a/Documentation/kernel-parameters.txt
> +++ b/Documentation/kernel-parameters.txt
> @@ -2148,6 +2148,8 @@ and is between 256 and 4096 characters. It is defined in the file
> Format: <reboot_mode>[,<reboot_mode2>[,...]]
> See arch/*/kernel/reboot.c or arch/*/kernel/process.c
>
> + readahead= Default readahead value for block devices.
> +

I think the description should define the units (kb) and valid value
ranges e.g. page size to something not excessive - say 65536kb. The
above description is, IMO, useless without refering to the source to
find out this information....

[snip]

> @@ -249,6 +250,24 @@ static int __init loglevel(char *str)
>
> early_param("loglevel", loglevel);
>
> +static int __init readahead(char *str)
> +{
> + unsigned long readahead_kb;
> +
> + if (!str)
> + return -EINVAL;
> + readahead_kb = memparse(str, &str) / 1024ULL;
> + if (*str != '\0')
> + return -EINVAL;

And readahead_kb needs to be validated against the range of
valid values here.

> +
> + vm_max_readahead_kb = readahead_kb;
> + default_backing_dev_info.ra_pages = vm_max_readahead_kb
> + * 1024 / PAGE_CACHE_SIZE;
> + return 0;
> +}
> +
> +early_param("readahead", readahead);
> +

Cheers,

Dave.
--
Dave Chinner
david(a)fromorbit.com
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From: Nikanth Karthikesan on 14 Feb 2010 23:40
On Thursday 11 February 2010 20:46:51 Wu Fengguang wrote:
> Nikanth,
>
> > From: Nikanth Karthikesan <knikanth(a)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.
>
> The patch looks good to me, though it conflicts with my patches.
> Do you mind me including a modified version in my readahead patchset?
>

Sure, go ahead.

Thanks
Nikanth
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