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.
Signed-off-by: Stefan Hengelein <[email protected]> Signed-off-by: Florian Schmaus <[email protected]> Signed-off-by: Andor Daam <[email protected]> Signed-off-by: Dan Magenheimer <[email protected]> [v1: Fixes per Seth Jennings suggestions] [v2: Removed FRONTSWAP_HAS_.. ] [v3: Fix up per Bob Liu <[email protected]> recommendations] Signed-off-by: Konrad Rzeszutek Wilk <[email protected]> --- mm/frontswap.c | 66 +++++++++++++++++++++++++++++++++++++++++++++++-------- 1 files changed, 56 insertions(+), 10 deletions(-) diff --git a/mm/frontswap.c b/mm/frontswap.c index 2890e67..ba58157 100644 --- 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 + * 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. + * 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)) + (*frontswap_ops.init)(i); + } + /* 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); @@ -119,10 +141,17 @@ void __frontswap_init(unsigned type) { struct swap_info_struct *sis = swap_info[type]; - BUG_ON(sis == NULL); - if (sis->frontswap_map == NULL) - return; - frontswap_ops.init(type); + if (backend_registered) { + BUG_ON(sis == NULL); + if (sis->frontswap_map == NULL) + return; + (*frontswap_ops.init)(type); + } + else { + BUG_ON(type > MAX_SWAPFILES); + set_bit(type, need_init); + } + } EXPORT_SYMBOL(__frontswap_init); @@ -147,6 +176,11 @@ int __frontswap_store(struct page *page) struct swap_info_struct *sis = swap_info[type]; pgoff_t offset = swp_offset(entry); + if (!backend_registered) { + inc_frontswap_failed_stores(); + return ret; + } + BUG_ON(!PageLocked(page)); BUG_ON(sis == NULL); if (frontswap_test(sis, offset)) @@ -186,6 +220,9 @@ int __frontswap_load(struct page *page) struct swap_info_struct *sis = swap_info[type]; pgoff_t offset = swp_offset(entry); + if (!backend_registered) + return ret; + BUG_ON(!PageLocked(page)); BUG_ON(sis == NULL); if (frontswap_test(sis, offset)) @@ -209,6 +246,9 @@ void __frontswap_invalidate_page(unsigned type, pgoff_t offset) { struct swap_info_struct *sis = swap_info[type]; + if (!backend_registered) + return; + BUG_ON(sis == NULL); if (frontswap_test(sis, offset)) { frontswap_ops.invalidate_page(type, offset); @@ -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); + + frontswap_enabled = 1; return 0; } -- 1.7.7.6 -- 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/
