> From: Seth Jennings [mailto:sjenn...@linux.vnet.ibm.com]
> Subject: Re: [PATCH 2/5] mm: frontswap: lazy initialization to allow tmem
> backends to build/run as
> modules
>
> > static int __init init_frontswap(void)
> > {
> > + int i;
> > #ifdef CONFIG_DEBUG_FS
> > struct dentry *root = debugfs_create_dir("frontswap", NULL);
> > if (root == NULL)
> > @@ -364,6 +414,10 @@ static int __init init_frontswap(void)
> > debugfs_create_u64("invalidates", S_IRUGO,
> > root, &frontswap_invalidates);
> > #endif
> > + for (i = 0; i < MAX_INITIALIZABLE_SD; i++)
> > + sds[i] = -1;
> > +
> > + frontswap_enabled = 1;
>
> If frontswap_enabled is going to be on all the time, then what point
> does it serve? By extension, can all of the static inline wrappers in
> frontswap.h be done away with?
The intent of frontswap_enabled and cleancache_enabled was
to avoid the overhead of a function call at the point where
each frontswap/cleancache "hooks" is placed, using a global
variable check instead. I'm not sure if this minor
performance tuning effort is worth preserving: If not,
I agree frontswap_enabled and the static inline wrappers (as
well as their cleancache brethren) could be done away with **;
if worth preserving, then I think frontswap_enabled could
be set in the init method instead but the check for enabled
in the frontswap init method and the cleancache init_fs
method would need to be removed else lazy initialization
wouldn't work.
Dan
** Note to anyone that tries this: There is a subtle but
clever hack in the wrappers suggested by Jeremy Fitzhardinge
that disables the wrappers at compile-time as well as
runtime. IOW, make sure you test-compile both with
CONFIG_{CLEANCACHE|FRONTSWAP} _and_ with them unconfig'd.
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