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Message-ID: <20121102182749.GB30100@konrad-lan.dumpdata.com>
Date: Fri, 2 Nov 2012 14:27:49 -0400
From: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To: Seth Jennings <sjenning@...ux.vnet.ibm.com>
Cc: 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 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;
+
/*
* 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);
+ }
}
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);
+ }
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;
+
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);
+ }
}
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;
return 0;
}
--
1.7.11.7
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