On Monday 15 February 2010 03:07:24 Dave Chinner wrote:
> 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@xxxxxxx>
> >
> > 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@xxxxxxx>
> >
> > ---
> >
> > 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....
>
The parameter can be specified with/without any suffix(k/m/g) that memparse()
helper function can accept. So it can take 1M, 1024k, 1050620. I checked other
parameters that use memparse() to get similar values and they didn't document
it. May be this should be described here.
> [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.
>
I didn't want to impose artificial restrictions. I think Wu's patch set would
be adding some restrictions, like minimum readahead. He could fix it when he
modifies the patch to include in his patch set.
> > +
> > + 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);
> > +
>
Thanks for reviewing.
Thanks
Nikanth
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