Re: [PATCH] fs: use kmalloc() to allocate fdmem if possible

[Avi Kivity]

On 05/03/2010 03:15 AM, Tetsuo Handa wrote:
> Avi Kivity wrote:
>    
> > On 05/02/2010 07:46 PM, Changli Gao wrote:
> >      
> > > use kmalloc() to allocate fdmem if possible.
> > >
> > > vmalloc() is used as a fallback solution for fdmem allocation. Two members are
> > > added into the hole of the structure fdtable to indicate if vmalloc() is used
> > > or not.
> > >
> > >
> > > diff --git a/fs/file.c b/fs/file.c
> > > index 34bb7f7..f71dd85 100644
> > > --- a/fs/file.c
> > > +++ b/fs/file.c
> > > @@ -39,28 +39,34 @@ int sysctl_nr_open_max = 1024 * 1024; /* raised later */
> > >     */
> > >    static DEFINE_PER_CPU(struct fdtable_defer, fdtable_defer_list);
> > >
> > > -static inline void * alloc_fdmem(unsigned int size)
> > > +static inline void *alloc_fdmem(unsigned int size, unsigned short *use_vmalloc)
> > >    {
> > > -	if (size<= PAGE_SIZE)
> > > -		return kmalloc(size, GFP_KERNEL);
> > > -	else
> > > -		return vmalloc(size);
> > > +	void *data;
> > > +
> > > +	data = kmalloc(size, GFP_KERNEL);
> > > +	if (data != NULL) {
> > > +		*use_vmalloc = 0;
> > > +		return data;
> > > +	}
> > > +	*use_vmalloc = 1;
> > > +
> > > +	return vmalloc(size);
> > >    }
> > >
> > >        
> > Perhaps vmalloc() should do this by itself?  vfree() can examine the
> > pointer and call kfree() if it isn't within the vmalloc address range.
> >      
> You can use is_vmalloc_addr().
>
> 	if (is_vmalloc_addr(p))
> 		vfree(p);
> 	else
> 		kfree(p);
>    


My point is, vmalloc() and vfree should do this, not their callers:

vmalloc(size):
    if (size <= PAGE_SIZE)
        return kmalloc(size, GFP_KERNEL);
    ...

vfree(p):
    if (!is_vmalloc_addr(p) {
        kfree(p);
        return;
    }
    ...

--
Do not meddle in the internals of kernels, for they are subtle and quick to panic.

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