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Message-ID: <CAA_GA1e3ACs8v5955S8xfSVomT3niq0_PfLO23QpBMR6OoB5UQ@mail.gmail.com>
Date: Sat, 3 Nov 2012 09:21:28 +0800
From: Bob Liu <lliubbo@...il.com>
To: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Cc: Seth Jennings <sjenning@...ux.vnet.ibm.com>,
Dan Magenheimer <dan.magenheimer@...cle.com>,
devel@...uxdriverproject.org, linux-kernel@...r.kernel.org,
gregkh@...uxfoundation.org, linux-mm@...ck.org, ngupta@...are.org,
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 Sat, Nov 3, 2012 at 2:27 AM, Konrad Rzeszutek Wilk
<konrad.wilk@...cle.com> wrote:
> On Wed, Oct 31, 2012 at 12:05:32PM -0500, Seth Jennings wrote:
>> 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;
>
>
> How does this look? (I hadn't actually tested it, but did compile test
> it)
>
> From f545530e9ef2b0623ab9e78d490595e3b7eaa3fa Mon Sep 17 00:00:00 2001
> From: Dan Magenheimer <dan.magenheimer@...cle.com>
> Date: Wed, 31 Oct 2012 08:07:51 -0700
> Subject: [PATCH 2/2] mm: frontswap: lazy initialization to allow tmem
> backends to build/run as modules
>
> 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>
> [v1: Fixes per Seth Jennings suggestions]
> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
> ---
> include/linux/frontswap.h | 1 +
> mm/frontswap.c | 59 +++++++++++++++++++++++++++++++++++++++++------
> 2 files changed, 53 insertions(+), 7 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..4e04549 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(sds, MAX_SWAPFILES);
> +static bool backend_registered __read_mostly;
> +
Yes, i also prefer to use bitmap and resue MAX_SWAPFILES.
> /*
> * Register operations for frontswap, returning previous thus allowing
> * detection of multiple backends and possible nesting.
> @@ -87,9 +99,16 @@ 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 = true;
> + for (i = 0; i < MAX_SWAPFILES; i++) {
> + if (test_bit(i, sds))
> + (*frontswap_ops.init)(sds[i]);
> + }
> return old;
> }
> EXPORT_SYMBOL(frontswap_register_ops);
> @@ -122,7 +141,10 @@ 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);
> + set_bit(type, sds);
> + }
> }
What about set bit if backend not registered and clear bit when invalidate.
I think that looks more directly.
Like:
+ 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, sds);
+ }
> EXPORT_SYMBOL(__frontswap_init);
>
> @@ -147,10 +169,20 @@ 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_SWAPFILES && !test_bit(type, sds)) {
> + /* lazy init call to handle post-boot insmod backends*/
> + (*frontswap_ops.init)(type);
> + set_bit(type, sds);
> + }
Then rm this.
> ret = frontswap_ops.store(type, offset, page);
> if (ret == 0) {
> frontswap_set(sis, offset);
> @@ -186,6 +218,9 @@ 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 +244,9 @@ void __frontswap_invalidate_page(unsigned type, pgoff_t offset)
> {
> struct swap_info_struct *sis = swap_info[type];
>
> + if (!backend_registered)
> + return;
> +
I'm not sure whether __frontswap_invalidate_page() will be called if
backend not registered.
> BUG_ON(sis == NULL);
> if (frontswap_test(sis, offset)) {
> frontswap_ops.invalidate_page(type, offset);
> @@ -226,12 +264,16 @@ 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));
> + } else {
> + bitmap_zero(sds, MAX_SWAPFILES);
Use clear_bit(type, sds) here;
> + }
> }
> EXPORT_SYMBOL(__frontswap_invalidate_area);
>
> @@ -364,6 +406,9 @@ static int __init init_frontswap(void)
> debugfs_create_u64("invalidates", S_IRUGO,
> root, &frontswap_invalidates);
> #endif
> + bitmap_zero(sds, MAX_SWAPFILES);
> +
> + frontswap_enabled = 1;
We'd better init backend_registered = false also.
> return 0;
> }
>
> --
> 1.7.11.7
>
> --
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--
Thanks,
--Bob
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