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Date: Wed, 31 Oct 2012 12:05:32 -0500
From: Seth Jennings <sjenning@...ux.vnet.ibm.com>
To: Dan Magenheimer <dan.magenheimer@...cle.com>
CC: devel@...uxdriverproject.org, linux-kernel@...r.kernel.org,
gregkh@...uxfoundation.org, linux-mm@...ck.org, ngupta@...are.org,
konrad.wilk@...cle.com, minchan@...nel.org, fschmaus@...il.com,
andor.daam@...glemail.com, ilendir@...glemail.com,
akpm@...ux-foundation.org, mgorman@...e.de
Subject: Re: [PATCH 2/5] mm: frontswap: lazy initialization to allow tmem
backends to build/run as modules
On 10/31/2012 10:07 AM, Dan Magenheimer wrote:
> 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 <ilendir@...glemail.com>
> Signed-off-by: Florian Schmaus <fschmaus@...il.com>
> Signed-off-by: Andor Daam <andor.daam@...glemail.com>
> Signed-off-by: Dan Magenheimer <dan.magenheimer@...cle.com>
> ---
> include/linux/frontswap.h | 1 +
> mm/frontswap.c | 70 +++++++++++++++++++++++++++++++++++++++-----
> 2 files changed, 63 insertions(+), 8 deletions(-)
>
> diff --git a/include/linux/frontswap.h b/include/linux/frontswap.h
> index 3044254..ef6ada6 100644
> --- a/include/linux/frontswap.h
> +++ b/include/linux/frontswap.h
> @@ -23,6 +23,7 @@ extern void frontswap_writethrough(bool);
> extern void frontswap_tmem_exclusive_gets(bool);
>
> extern void __frontswap_init(unsigned type);
> +#define FRONTSWAP_HAS_LAZY_INIT
> extern int __frontswap_store(struct page *page);
> extern int __frontswap_load(struct page *page);
> extern void __frontswap_invalidate_page(unsigned, pgoff_t);
> diff --git a/mm/frontswap.c b/mm/frontswap.c
> index 2890e67..523a19b 100644
> --- a/mm/frontswap.c
> +++ b/mm/frontswap.c
> @@ -80,6 +80,19 @@ 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.
> + */
> +#define MAX_INITIALIZABLE_SD 32
MAX_INITIALIZABLE_SD should just be MAX_SWAPFILES
> +static int sds[MAX_INITIALIZABLE_SD];
Rather than store and array of enabled types indexed by type, why not
an array of booleans indexed by type. Or a bitfield if you really
want to save space.
> +static int backend_registered;
(backend_registered) is equivalent to checking (frontswap_ops != NULL)
right?
> +
> /*
> * Register operations for frontswap, returning previous thus allowing
> * detection of multiple backends and possible nesting.
> @@ -87,9 +100,16 @@ 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;
> +
> + backend_registered = 1;
> + for (i = 0; i < MAX_INITIALIZABLE_SD; i++) {
> + if (sds[i] != -1)
> + (*frontswap_ops.init)(sds[i]);
> + }
> return old;
> }
> EXPORT_SYMBOL(frontswap_register_ops);
> @@ -122,7 +142,10 @@ void __frontswap_init(unsigned type)
> BUG_ON(sis == NULL);
> if (sis->frontswap_map == NULL)
> return;
> - frontswap_ops.init(type);
> + if (backend_registered) {
> + (*frontswap_ops.init)(type);
> + sds[type] = type;
This is weird, storing the type in an array indexed by type. Hence my
suggestion above about an array of booleans or a bitfield.
> + }
> }
> EXPORT_SYMBOL(__frontswap_init);
>
> @@ -147,10 +170,20 @@ 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))
> dup = 1;
> + if (type < MAX_INITIALIZABLE_SD && sds[type] == -1) {
> + /* lazy init call to handle post-boot insmod backends*/
> + (*frontswap_ops.init)(type);
> + sds[type] = type;
> + }
> ret = frontswap_ops.store(type, offset, page);
> if (ret == 0) {
> frontswap_set(sis, offset);
> @@ -186,6 +219,9 @@ 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 +245,9 @@ 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);
> @@ -225,13 +264,23 @@ EXPORT_SYMBOL(__frontswap_invalidate_page);
> 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));
> + int i;
> +
> + 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));
> + } else {
> + for (i = 0; i < MAX_INITIALIZABLE_SD; i++) {
> + if (sds[i] == type) {
Additional weirdness with sds. It seems this whole for loop could
just be reduced to:
sds[type] = -1;
> + sds[i] = -1;
> + break;
> + }
> + }
> + }
> }
> EXPORT_SYMBOL(__frontswap_invalidate_area);
>
> @@ -353,6 +402,7 @@ EXPORT_SYMBOL(frontswap_curr_pages);
>
> 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?
--
Seth
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