On Wed, 11 Mar 2009 15:11:17 -0700
Dave Hansen <dave@xxxxxxxxxxxxxxxxxx> wrote:
> I'm feeling a bit better about these, although I am still honestly quite
> afraid of the barriers. I also didn't like all the #ifdefs much, but
> here's some help on that.
Do we need the ifdefs at all?
> How about this on top of what you have as a bit of a cleanup? It gets
> rid of all the new #ifdefs in .c files?
>
> Did I miss the use of get_mnt_writers_ptr()? I don't think I actually
> saw it used anywhere in this pair of patches, so I've stolen it. I
> think gcc should compile all this new stuff down to be basically the
> same as you had before. The one thing I'm not horribly sure of is the
> "out_free_devname:" label. It shouldn't be reachable in the !SMP case.
>
> I could also consolidate the header #ifdefs into a single one if you
> think that looks better.
>
> This is just compile tested, btw.
>
> ---
>
> linux-2.6.git-dave/fs/namespace.c | 35 ++++++-------------------------
> linux-2.6.git-dave/include/linux/mount.h | 30 ++++++++++++++++++++++++--
> 2 files changed, 35 insertions(+), 30 deletions(-)
>
> diff -puN include/linux/mount.h~move-ifdefs-take2 include/linux/mount.h
> --- linux-2.6.git/include/linux/mount.h~move-ifdefs-take2 2009-03-11 15:01:10.000000000 -0700
> +++ linux-2.6.git-dave/include/linux/mount.h 2009-03-11 15:02:01.000000000 -0700
> @@ -71,15 +71,41 @@ struct vfsmount {
> #endif
> };
>
> -static inline int *get_mnt_writers_ptr(struct vfsmount *mnt)
> +static inline int *get_mnt_writers_ptr_cpu(struct vfsmount *mnt,
> + int cpu)
> {
> #ifdef CONFIG_SMP
> - return mnt->mnt_writers;
> + return per_cpu_ptr(mnt->mnt_writers, cpu);
> #else
> return &mnt->mnt_writers;
> #endif
> }
>
> +static inline int *get_mnt_writers_ptr(struct vfsmount *mnt)
> +{
> + return get_mnt_writers_ptr_cpu(mnt, smp_processor_id());
> +}
> +
> +static inline int alloc_mnt_writers(struct vfsmount *mnt)
> +{
> +#ifdef CONFIG_SMP
> + mnt->mnt_writers = alloc_percpu(int);
> + if (!mnt->mnt_writers)
> + return -ENOMEM;
> +#else
> + mnt->mnt_writers = 0;
> +#endif
> + return 0;
> +}
If the CONFIG_SMP=n code is just removed, the percpu code should dtrt
with CONFIG_SMP=n. There is the additional pointer indirection though,
I guess. Do we do it often enough to be concerned about the cost?
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