On Wed, 14 Nov 2012 13:57:06 -0500 Konrad Rzeszutek Wilk <[email protected]> wrote:
> From: Dan Magenheimer <[email protected]> > > With the goal of allowing tmem backends (zcache, ramster, Xen tmem) to be > built/loaded as modules rather than built-in and enabled by a boot parameter, > this patch provides "lazy initialization", allowing backends to register to > frontswap even after swapon was run. Before a backend registers all calls > to init are recorded and the creation of tmem_pools delayed until a backend > registers or until a frontswap put is attempted. > > > ... > > --- a/mm/frontswap.c > +++ b/mm/frontswap.c > @@ -80,6 +80,18 @@ static inline void inc_frontswap_succ_stores(void) { } > static inline void inc_frontswap_failed_stores(void) { } > static inline void inc_frontswap_invalidates(void) { } > #endif > + > +/* > + * When no backend is registered all calls to init are registered and What is "init"? Spell it out fully, please. > + * remembered but fail to create tmem_pools. When a backend registers with > + * frontswap the previous calls to init are executed to create tmem_pools > + * and set the respective poolids. Again, seems really hacky. Why can't we just change callers so they call things in the correct order? > + * While no backend is registered all "puts", "gets" and "flushes" are > + * ignored or fail. > + */ > +static DECLARE_BITMAP(need_init, MAX_SWAPFILES); > +static bool backend_registered __read_mostly; > + > /* > * Register operations for frontswap, returning previous thus allowing > * detection of multiple backends and possible nesting. > @@ -87,9 +99,19 @@ static inline void inc_frontswap_invalidates(void) { } > struct frontswap_ops frontswap_register_ops(struct frontswap_ops *ops) > { > struct frontswap_ops old = frontswap_ops; > + int i; > > frontswap_ops = *ops; > frontswap_enabled = true; > + > + for (i = 0; i < MAX_SWAPFILES; i++) { > + if (test_and_clear_bit(i, need_init)) ooh, that wasn't racy ;) > + (*frontswap_ops.init)(i); > + } > + /* We MUST have backend_registered called _after_ the frontswap_init's > + * have been called. Otherwise __frontswap_store might fail. */ Comment makes no sense - backend_registered is not a function. Also, let's lay the comments out conventionally please: /* * We MUST have backend_registered called _after_ the frontswap_init's * have been called. Otherwise __frontswap_store might fail. */ > + barrier(); > + backend_registered = true; > return old; > } > EXPORT_SYMBOL(frontswap_register_ops); > > ... > > @@ -226,12 +266,15 @@ void __frontswap_invalidate_area(unsigned type) > { > struct swap_info_struct *sis = swap_info[type]; > > - BUG_ON(sis == NULL); > - if (sis->frontswap_map == NULL) > - return; > - frontswap_ops.invalidate_area(type); > - atomic_set(&sis->frontswap_pages, 0); > - memset(sis->frontswap_map, 0, sis->max / sizeof(long)); > + if (backend_registered) { > + BUG_ON(sis == NULL); > + if (sis->frontswap_map == NULL) > + return; > + (*frontswap_ops.invalidate_area)(type); > + atomic_set(&sis->frontswap_pages, 0); > + memset(sis->frontswap_map, 0, sis->max / sizeof(long)); > + } > + clear_bit(type, need_init); > } > EXPORT_SYMBOL(__frontswap_invalidate_area); > > @@ -364,6 +407,9 @@ static int __init init_frontswap(void) > debugfs_create_u64("invalidates", S_IRUGO, > root, &frontswap_invalidates); > #endif > + bitmap_zero(need_init, MAX_SWAPFILES); unneeded? > + frontswap_enabled = 1; > return 0; > } > > ... > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
