Re: [PATCH 3/7] FS-Cache: Avoid ENFILE checking for kernel-specific open files

[David Howells <dhowells@redhat.com>]

Andrew Morton <akpm@osdl.org> wrote:

> >  static struct percpu_counter nr_files __cacheline_aligned_in_smp;
> > +static atomic_t nr_kernel_files;
> 
> So it's not performance-critical.

Hmmm... nowhere near as critical as the ENFILE accounting, plus the only place
we actually read it is for the sysctl file.

It could actually be dispensed with entirely, I suppose.

> > -struct file *get_empty_filp(void)
> > +struct file *get_empty_filp(int kernel)
> 
> I'd suggest a new get_empty_kernel_filp(void) rather than providing a magic
> argument.  (we can still have the magic argument in the new
> __get_empty_filp(int), but it shouldn't be part of the caller-visible API).
> ...
> It would be more flexible to make the caller pass in the flags directly.

So:

	struct file *get_empty_kernel_filp(unsigned short flags);

which devolves to get_empty_filp() if flags == 0?


> > +EXPORT_SYMBOL(fget_light);
> 
> fget_light is not otherwise referenced in this patch.

Good point.  I'll move it into the cachefiles patch.

> > +EXPORT_SYMBOL(dentry_open_kernel);
> 
> _GPL?

If you wish.

> That's unfortunate.  There's still room in f_flags.  Was it hard to use that?

Yeah... but the usage of f_flags is constrained by O_xxxx flags that are part
of the userspace interface.  Using those up for purely kernel things is a bad
idea.

Note that I've not actually increased the size of the struct file - f_mode is
a 16-bit value, hence why I chose an unsigned short.

> This changes the format of /proc/sys/fs/file-nr.  What will break?

As far as I can tell, not a lot.  I've grepped through various etc, lib and
bin directories on my FC5 system, and the only match I've found is:

	/usr/lib64/sa/sadc

I'll present the count through a separate file to make sure.

David