We will use percpu-refcount to serialize against concurrent swapoff. This
patch adds the percpu_ref support for swap.
Signed-off-by: Miaohe Lin <[email protected]>
---
include/linux/swap.h | 3 +++
mm/swapfile.c | 33 +++++++++++++++++++++++++++++----
2 files changed, 32 insertions(+), 4 deletions(-)
diff --git a/include/linux/swap.h b/include/linux/swap.h
index 144727041e78..8be36eb58b7a 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -240,6 +240,7 @@ struct swap_cluster_list {
* The in-memory structure used to track swap areas.
*/
struct swap_info_struct {
+ struct percpu_ref users; /* serialization against concurrent swapoff */
unsigned long flags; /* SWP_USED etc: see above */
signed short prio; /* swap priority of this type */
struct plist_node list; /* entry in swap_active_head */
@@ -260,6 +261,8 @@ struct swap_info_struct {
struct block_device *bdev; /* swap device or bdev of swap file */
struct file *swap_file; /* seldom referenced */
unsigned int old_block_size; /* seldom referenced */
+ bool ref_initialized; /* seldom referenced */
+ struct completion comp; /* seldom referenced */
#ifdef CONFIG_FRONTSWAP
unsigned long *frontswap_map; /* frontswap in-use, one bit per page */
atomic_t frontswap_pages; /* frontswap pages in-use counter */
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 149e77454e3c..66515a3a2824 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -39,6 +39,7 @@
#include <linux/export.h>
#include <linux/swap_slots.h>
#include <linux/sort.h>
+#include <linux/completion.h>
#include <asm/tlbflush.h>
#include <linux/swapops.h>
@@ -511,6 +512,14 @@ static void swap_discard_work(struct work_struct *work)
spin_unlock(&si->lock);
}
+static void swap_users_ref_free(struct percpu_ref *ref)
+{
+ struct swap_info_struct *si;
+
+ si = container_of(ref, struct swap_info_struct, users);
+ complete(&si->comp);
+}
+
static void alloc_cluster(struct swap_info_struct *si, unsigned long idx)
{
struct swap_cluster_info *ci = si->cluster_info;
@@ -2500,7 +2509,7 @@ static void enable_swap_info(struct swap_info_struct *p, int prio,
* Guarantee swap_map, cluster_info, etc. fields are valid
* between get/put_swap_device() if SWP_VALID bit is set
*/
- synchronize_rcu();
+ percpu_ref_resurrect(&p->users);
spin_lock(&swap_lock);
spin_lock(&p->lock);
_enable_swap_info(p);
@@ -2621,11 +2630,18 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
p->flags &= ~SWP_VALID; /* mark swap device as invalid */
spin_unlock(&p->lock);
spin_unlock(&swap_lock);
+
+ percpu_ref_kill(&p->users);
/*
- * wait for swap operations protected by get/put_swap_device()
- * to complete
+ * We need synchronize_rcu() here to protect the accessing
+ * to the swap cache data structure.
*/
synchronize_rcu();
+ /*
+ * Wait for swap operations protected by get/put_swap_device()
+ * to complete.
+ */
+ wait_for_completion(&p->comp);
flush_work(&p->discard_work);
@@ -3132,7 +3148,7 @@ static bool swap_discardable(struct swap_info_struct *si)
SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
{
struct swap_info_struct *p;
- struct filename *name;
+ struct filename *name = NULL;
struct file *swap_file = NULL;
struct address_space *mapping;
int prio;
@@ -3163,6 +3179,15 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
INIT_WORK(&p->discard_work, swap_discard_work);
+ if (!p->ref_initialized) {
+ error = percpu_ref_init(&p->users, swap_users_ref_free,
+ PERCPU_REF_INIT_DEAD, GFP_KERNEL);
+ if (unlikely(error))
+ goto bad_swap;
+ init_completion(&p->comp);
+ p->ref_initialized = true;
+ }
+
name = getname(specialfile);
if (IS_ERR(name)) {
error = PTR_ERR(name);
--
2.19.1
Miaohe Lin <[email protected]> writes:
> We will use percpu-refcount to serialize against concurrent swapoff. This
> patch adds the percpu_ref support for swap.
>
> Signed-off-by: Miaohe Lin <[email protected]>
> ---
> include/linux/swap.h | 3 +++
> mm/swapfile.c | 33 +++++++++++++++++++++++++++++----
> 2 files changed, 32 insertions(+), 4 deletions(-)
>
> diff --git a/include/linux/swap.h b/include/linux/swap.h
> index 144727041e78..8be36eb58b7a 100644
> --- a/include/linux/swap.h
> +++ b/include/linux/swap.h
> @@ -240,6 +240,7 @@ struct swap_cluster_list {
> * The in-memory structure used to track swap areas.
> */
> struct swap_info_struct {
> + struct percpu_ref users; /* serialization against concurrent swapoff */
The comments aren't general enough. We use this to check whether the
swap device has been fully initialized, etc. May be something as below?
/* indicate and keep swap device valid */
> unsigned long flags; /* SWP_USED etc: see above */
> signed short prio; /* swap priority of this type */
> struct plist_node list; /* entry in swap_active_head */
> @@ -260,6 +261,8 @@ struct swap_info_struct {
> struct block_device *bdev; /* swap device or bdev of swap file */
> struct file *swap_file; /* seldom referenced */
> unsigned int old_block_size; /* seldom referenced */
> + bool ref_initialized; /* seldom referenced */
> + struct completion comp; /* seldom referenced */
> #ifdef CONFIG_FRONTSWAP
> unsigned long *frontswap_map; /* frontswap in-use, one bit per page */
> atomic_t frontswap_pages; /* frontswap pages in-use counter */
> diff --git a/mm/swapfile.c b/mm/swapfile.c
> index 149e77454e3c..66515a3a2824 100644
> --- a/mm/swapfile.c
> +++ b/mm/swapfile.c
> @@ -39,6 +39,7 @@
> #include <linux/export.h>
> #include <linux/swap_slots.h>
> #include <linux/sort.h>
> +#include <linux/completion.h>
>
> #include <asm/tlbflush.h>
> #include <linux/swapops.h>
> @@ -511,6 +512,14 @@ static void swap_discard_work(struct work_struct *work)
> spin_unlock(&si->lock);
> }
>
> +static void swap_users_ref_free(struct percpu_ref *ref)
> +{
> + struct swap_info_struct *si;
> +
> + si = container_of(ref, struct swap_info_struct, users);
> + complete(&si->comp);
> +}
> +
> static void alloc_cluster(struct swap_info_struct *si, unsigned long idx)
> {
> struct swap_cluster_info *ci = si->cluster_info;
> @@ -2500,7 +2509,7 @@ static void enable_swap_info(struct swap_info_struct *p, int prio,
> * Guarantee swap_map, cluster_info, etc. fields are valid
> * between get/put_swap_device() if SWP_VALID bit is set
> */
> - synchronize_rcu();
You cannot remove this without changing get/put_swap_device(). It's
better to squash at least PATCH 1-2.
> + percpu_ref_resurrect(&p->users);
> spin_lock(&swap_lock);
> spin_lock(&p->lock);
> _enable_swap_info(p);
> @@ -2621,11 +2630,18 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
> p->flags &= ~SWP_VALID; /* mark swap device as invalid */
> spin_unlock(&p->lock);
> spin_unlock(&swap_lock);
> +
> + percpu_ref_kill(&p->users);
> /*
> - * wait for swap operations protected by get/put_swap_device()
> - * to complete
> + * We need synchronize_rcu() here to protect the accessing
> + * to the swap cache data structure.
> */
> synchronize_rcu();
> + /*
> + * Wait for swap operations protected by get/put_swap_device()
> + * to complete.
> + */
I think the comments (after some revision) can be moved before
percpu_ref_kill(). The synchronize_rcu() comments can be merged.
> + wait_for_completion(&p->comp);
>
> flush_work(&p->discard_work);
>
> @@ -3132,7 +3148,7 @@ static bool swap_discardable(struct swap_info_struct *si)
> SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
> {
> struct swap_info_struct *p;
> - struct filename *name;
> + struct filename *name = NULL;
> struct file *swap_file = NULL;
> struct address_space *mapping;
> int prio;
> @@ -3163,6 +3179,15 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
>
> INIT_WORK(&p->discard_work, swap_discard_work);
>
> + if (!p->ref_initialized) {
I don't think it's necessary to add another flag p->ref_initialized. We
can distinguish newly allocated and reused swap_info_struct in alloc_swap_info().
Best Regards,
Huang, Ying
> + error = percpu_ref_init(&p->users, swap_users_ref_free,
> + PERCPU_REF_INIT_DEAD, GFP_KERNEL);
> + if (unlikely(error))
> + goto bad_swap;
> + init_completion(&p->comp);
> + p->ref_initialized = true;
> + }
> +
> name = getname(specialfile);
> if (IS_ERR(name)) {
> error = PTR_ERR(name);
On 2021/4/19 10:48, Huang, Ying wrote:
> Miaohe Lin <[email protected]> writes:
>
>> We will use percpu-refcount to serialize against concurrent swapoff. This
>> patch adds the percpu_ref support for swap.
>>
>> Signed-off-by: Miaohe Lin <[email protected]>
>> ---
>> include/linux/swap.h | 3 +++
>> mm/swapfile.c | 33 +++++++++++++++++++++++++++++----
>> 2 files changed, 32 insertions(+), 4 deletions(-)
>>
>> diff --git a/include/linux/swap.h b/include/linux/swap.h
>> index 144727041e78..8be36eb58b7a 100644
>> --- a/include/linux/swap.h
>> +++ b/include/linux/swap.h
>> @@ -240,6 +240,7 @@ struct swap_cluster_list {
>> * The in-memory structure used to track swap areas.
>> */
>> struct swap_info_struct {
>> + struct percpu_ref users; /* serialization against concurrent swapoff */
>
> The comments aren't general enough. We use this to check whether the
> swap device has been fully initialized, etc. May be something as below?
>
> /* indicate and keep swap device valid */
Looks good.
>
>> unsigned long flags; /* SWP_USED etc: see above */
>> signed short prio; /* swap priority of this type */
>> struct plist_node list; /* entry in swap_active_head */
>> @@ -260,6 +261,8 @@ struct swap_info_struct {
>> struct block_device *bdev; /* swap device or bdev of swap file */
>> struct file *swap_file; /* seldom referenced */
>> unsigned int old_block_size; /* seldom referenced */
>> + bool ref_initialized; /* seldom referenced */
>> + struct completion comp; /* seldom referenced */
>> #ifdef CONFIG_FRONTSWAP
>> unsigned long *frontswap_map; /* frontswap in-use, one bit per page */
>> atomic_t frontswap_pages; /* frontswap pages in-use counter */
>> diff --git a/mm/swapfile.c b/mm/swapfile.c
>> index 149e77454e3c..66515a3a2824 100644
>> --- a/mm/swapfile.c
>> +++ b/mm/swapfile.c
>> @@ -39,6 +39,7 @@
>> #include <linux/export.h>
>> #include <linux/swap_slots.h>
>> #include <linux/sort.h>
>> +#include <linux/completion.h>
>>
>> #include <asm/tlbflush.h>
>> #include <linux/swapops.h>
>> @@ -511,6 +512,14 @@ static void swap_discard_work(struct work_struct *work)
>> spin_unlock(&si->lock);
>> }
>>
>> +static void swap_users_ref_free(struct percpu_ref *ref)
>> +{
>> + struct swap_info_struct *si;
>> +
>> + si = container_of(ref, struct swap_info_struct, users);
>> + complete(&si->comp);
>> +}
>> +
>> static void alloc_cluster(struct swap_info_struct *si, unsigned long idx)
>> {
>> struct swap_cluster_info *ci = si->cluster_info;
>> @@ -2500,7 +2509,7 @@ static void enable_swap_info(struct swap_info_struct *p, int prio,
>> * Guarantee swap_map, cluster_info, etc. fields are valid
>> * between get/put_swap_device() if SWP_VALID bit is set
>> */
>> - synchronize_rcu();
>
> You cannot remove this without changing get/put_swap_device(). It's
> better to squash at least PATCH 1-2.
Will squash PATCH 1-2. Thanks.
>
>> + percpu_ref_resurrect(&p->users);
>> spin_lock(&swap_lock);
>> spin_lock(&p->lock);
>> _enable_swap_info(p);
>> @@ -2621,11 +2630,18 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
>> p->flags &= ~SWP_VALID; /* mark swap device as invalid */
>> spin_unlock(&p->lock);
>> spin_unlock(&swap_lock);
>> +
>> + percpu_ref_kill(&p->users);
>> /*
>> - * wait for swap operations protected by get/put_swap_device()
>> - * to complete
>> + * We need synchronize_rcu() here to protect the accessing
>> + * to the swap cache data structure.
>> */
>> synchronize_rcu();
>> + /*
>> + * Wait for swap operations protected by get/put_swap_device()
>> + * to complete.
>> + */
>
> I think the comments (after some revision) can be moved before
> percpu_ref_kill(). The synchronize_rcu() comments can be merged.
>
Ok.
>> + wait_for_completion(&p->comp);
>>
>> flush_work(&p->discard_work);
>>
>> @@ -3132,7 +3148,7 @@ static bool swap_discardable(struct swap_info_struct *si)
>> SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
>> {
>> struct swap_info_struct *p;
>> - struct filename *name;
>> + struct filename *name = NULL;
>> struct file *swap_file = NULL;
>> struct address_space *mapping;
>> int prio;
>> @@ -3163,6 +3179,15 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
>>
>> INIT_WORK(&p->discard_work, swap_discard_work);
>>
>> + if (!p->ref_initialized) {
>
> I don't think it's necessary to add another flag p->ref_initialized. We
> can distinguish newly allocated and reused swap_info_struct in alloc_swap_info().
>
If newly allocated swap_info_struct failed to init percpu_ref, it will be considered as
a reused one in alloc_swap_info() _but_ the field users of swap_info_struct is actually
uninitialized. Does this make sense for you?
Many Thanks for quick review.
> Best Regards,
> Huang, Ying
>
>> + error = percpu_ref_init(&p->users, swap_users_ref_free,
>> + PERCPU_REF_INIT_DEAD, GFP_KERNEL);
>> + if (unlikely(error))
>> + goto bad_swap;
>> + init_completion(&p->comp);
>> + p->ref_initialized = true;
>> + }
>> +
>> name = getname(specialfile);
>> if (IS_ERR(name)) {
>> error = PTR_ERR(name);
> .
>
Miaohe Lin <[email protected]> writes:
> On 2021/4/19 10:48, Huang, Ying wrote:
>> Miaohe Lin <[email protected]> writes:
>>
>>> We will use percpu-refcount to serialize against concurrent swapoff. This
>>> patch adds the percpu_ref support for swap.
>>>
>>> Signed-off-by: Miaohe Lin <[email protected]>
>>> ---
>>> include/linux/swap.h | 3 +++
>>> mm/swapfile.c | 33 +++++++++++++++++++++++++++++----
>>> 2 files changed, 32 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/include/linux/swap.h b/include/linux/swap.h
>>> index 144727041e78..8be36eb58b7a 100644
>>> --- a/include/linux/swap.h
>>> +++ b/include/linux/swap.h
>>> @@ -240,6 +240,7 @@ struct swap_cluster_list {
>>> * The in-memory structure used to track swap areas.
>>> */
>>> struct swap_info_struct {
>>> + struct percpu_ref users; /* serialization against concurrent swapoff */
>>
>> The comments aren't general enough. We use this to check whether the
>> swap device has been fully initialized, etc. May be something as below?
>>
>> /* indicate and keep swap device valid */
>
> Looks good.
>
>>
>>> unsigned long flags; /* SWP_USED etc: see above */
>>> signed short prio; /* swap priority of this type */
>>> struct plist_node list; /* entry in swap_active_head */
>>> @@ -260,6 +261,8 @@ struct swap_info_struct {
>>> struct block_device *bdev; /* swap device or bdev of swap file */
>>> struct file *swap_file; /* seldom referenced */
>>> unsigned int old_block_size; /* seldom referenced */
>>> + bool ref_initialized; /* seldom referenced */
>>> + struct completion comp; /* seldom referenced */
>>> #ifdef CONFIG_FRONTSWAP
>>> unsigned long *frontswap_map; /* frontswap in-use, one bit per page */
>>> atomic_t frontswap_pages; /* frontswap pages in-use counter */
>>> diff --git a/mm/swapfile.c b/mm/swapfile.c
>>> index 149e77454e3c..66515a3a2824 100644
>>> --- a/mm/swapfile.c
>>> +++ b/mm/swapfile.c
>>> @@ -39,6 +39,7 @@
>>> #include <linux/export.h>
>>> #include <linux/swap_slots.h>
>>> #include <linux/sort.h>
>>> +#include <linux/completion.h>
>>>
>>> #include <asm/tlbflush.h>
>>> #include <linux/swapops.h>
>>> @@ -511,6 +512,14 @@ static void swap_discard_work(struct work_struct *work)
>>> spin_unlock(&si->lock);
>>> }
>>>
>>> +static void swap_users_ref_free(struct percpu_ref *ref)
>>> +{
>>> + struct swap_info_struct *si;
>>> +
>>> + si = container_of(ref, struct swap_info_struct, users);
>>> + complete(&si->comp);
>>> +}
>>> +
>>> static void alloc_cluster(struct swap_info_struct *si, unsigned long idx)
>>> {
>>> struct swap_cluster_info *ci = si->cluster_info;
>>> @@ -2500,7 +2509,7 @@ static void enable_swap_info(struct swap_info_struct *p, int prio,
>>> * Guarantee swap_map, cluster_info, etc. fields are valid
>>> * between get/put_swap_device() if SWP_VALID bit is set
>>> */
>>> - synchronize_rcu();
>>
>> You cannot remove this without changing get/put_swap_device(). It's
>> better to squash at least PATCH 1-2.
>
> Will squash PATCH 1-2. Thanks.
>
>>
>>> + percpu_ref_resurrect(&p->users);
>>> spin_lock(&swap_lock);
>>> spin_lock(&p->lock);
>>> _enable_swap_info(p);
>>> @@ -2621,11 +2630,18 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
>>> p->flags &= ~SWP_VALID; /* mark swap device as invalid */
>>> spin_unlock(&p->lock);
>>> spin_unlock(&swap_lock);
>>> +
>>> + percpu_ref_kill(&p->users);
>>> /*
>>> - * wait for swap operations protected by get/put_swap_device()
>>> - * to complete
>>> + * We need synchronize_rcu() here to protect the accessing
>>> + * to the swap cache data structure.
>>> */
>>> synchronize_rcu();
>>> + /*
>>> + * Wait for swap operations protected by get/put_swap_device()
>>> + * to complete.
>>> + */
>>
>> I think the comments (after some revision) can be moved before
>> percpu_ref_kill(). The synchronize_rcu() comments can be merged.
>>
>
> Ok.
>
>>> + wait_for_completion(&p->comp);
>>>
>>> flush_work(&p->discard_work);
>>>
>>> @@ -3132,7 +3148,7 @@ static bool swap_discardable(struct swap_info_struct *si)
>>> SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
>>> {
>>> struct swap_info_struct *p;
>>> - struct filename *name;
>>> + struct filename *name = NULL;
>>> struct file *swap_file = NULL;
>>> struct address_space *mapping;
>>> int prio;
>>> @@ -3163,6 +3179,15 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
>>>
>>> INIT_WORK(&p->discard_work, swap_discard_work);
>>>
>>> + if (!p->ref_initialized) {
>>
>> I don't think it's necessary to add another flag p->ref_initialized. We
>> can distinguish newly allocated and reused swap_info_struct in alloc_swap_info().
>>
>
> If newly allocated swap_info_struct failed to init percpu_ref, it will be considered as
> a reused one in alloc_swap_info() _but_ the field users of swap_info_struct is actually
> uninitialized. Does this make sense for you?
We can call percpu_ref_init() just after kvzalloc() in alloc_swap_info().
Best Regards,
Huang, Ying
> Many Thanks for quick review.
>
>> Best Regards,
>> Huang, Ying
>>
>>> + error = percpu_ref_init(&p->users, swap_users_ref_free,
>>> + PERCPU_REF_INIT_DEAD, GFP_KERNEL);
>>> + if (unlikely(error))
>>> + goto bad_swap;
>>> + init_completion(&p->comp);
>>> + p->ref_initialized = true;
>>> + }
>>> +
>>> name = getname(specialfile);
>>> if (IS_ERR(name)) {
>>> error = PTR_ERR(name);
>> .
>>
On 2021/4/19 15:52, Huang, Ying wrote:
> Miaohe Lin <[email protected]> writes:
>
>> On 2021/4/19 15:09, Huang, Ying wrote:
>>> Miaohe Lin <[email protected]> writes:
>>>
>>>> On 2021/4/19 10:48, Huang, Ying wrote:
>>>>> Miaohe Lin <[email protected]> writes:
>>>>>
>>>>>> We will use percpu-refcount to serialize against concurrent swapoff. This
>>>>>> patch adds the percpu_ref support for swap.
>>>>>>
>>>>>> Signed-off-by: Miaohe Lin <[email protected]>
>>>>>> ---
>>>>>> include/linux/swap.h | 3 +++
>>>>>> mm/swapfile.c | 33 +++++++++++++++++++++++++++++----
>>>>>> 2 files changed, 32 insertions(+), 4 deletions(-)
>>>>>>
>>>>>> diff --git a/include/linux/swap.h b/include/linux/swap.h
>>>>>> index 144727041e78..8be36eb58b7a 100644
>>>>>> --- a/include/linux/swap.h
>>>>>> +++ b/include/linux/swap.h
>>>>>> @@ -240,6 +240,7 @@ struct swap_cluster_list {
>>>>>> * The in-memory structure used to track swap areas.
>>>>>> */
>>>>>> struct swap_info_struct {
>>>>>> + struct percpu_ref users; /* serialization against concurrent swapoff */
>>>>>
>>>>> The comments aren't general enough. We use this to check whether the
>>>>> swap device has been fully initialized, etc. May be something as below?
>>>>>
>>>>> /* indicate and keep swap device valid */
>>>>
>>>> Looks good.
>>>>
>>>>>
>>>>>> unsigned long flags; /* SWP_USED etc: see above */
>>>>>> signed short prio; /* swap priority of this type */
>>>>>> struct plist_node list; /* entry in swap_active_head */
>>>>>> @@ -260,6 +261,8 @@ struct swap_info_struct {
>>>>>> struct block_device *bdev; /* swap device or bdev of swap file */
>>>>>> struct file *swap_file; /* seldom referenced */
>>>>>> unsigned int old_block_size; /* seldom referenced */
>>>>>> + bool ref_initialized; /* seldom referenced */
>>>>>> + struct completion comp; /* seldom referenced */
>>>>>> #ifdef CONFIG_FRONTSWAP
>>>>>> unsigned long *frontswap_map; /* frontswap in-use, one bit per page */
>>>>>> atomic_t frontswap_pages; /* frontswap pages in-use counter */
>>>>>> diff --git a/mm/swapfile.c b/mm/swapfile.c
>>>>>> index 149e77454e3c..66515a3a2824 100644
>>>>>> --- a/mm/swapfile.c
>>>>>> +++ b/mm/swapfile.c
>>>>>> @@ -39,6 +39,7 @@
>>>>>> #include <linux/export.h>
>>>>>> #include <linux/swap_slots.h>
>>>>>> #include <linux/sort.h>
>>>>>> +#include <linux/completion.h>
>>>>>>
>>>>>> #include <asm/tlbflush.h>
>>>>>> #include <linux/swapops.h>
>>>>>> @@ -511,6 +512,14 @@ static void swap_discard_work(struct work_struct *work)
>>>>>> spin_unlock(&si->lock);
>>>>>> }
>>>>>>
>>>>>> +static void swap_users_ref_free(struct percpu_ref *ref)
>>>>>> +{
>>>>>> + struct swap_info_struct *si;
>>>>>> +
>>>>>> + si = container_of(ref, struct swap_info_struct, users);
>>>>>> + complete(&si->comp);
>>>>>> +}
>>>>>> +
>>>>>> static void alloc_cluster(struct swap_info_struct *si, unsigned long idx)
>>>>>> {
>>>>>> struct swap_cluster_info *ci = si->cluster_info;
>>>>>> @@ -2500,7 +2509,7 @@ static void enable_swap_info(struct swap_info_struct *p, int prio,
>>>>>> * Guarantee swap_map, cluster_info, etc. fields are valid
>>>>>> * between get/put_swap_device() if SWP_VALID bit is set
>>>>>> */
>>>>>> - synchronize_rcu();
>>>>>
>>>>> You cannot remove this without changing get/put_swap_device(). It's
>>>>> better to squash at least PATCH 1-2.
>>>>
>>>> Will squash PATCH 1-2. Thanks.
>>>>
>>>>>
>>>>>> + percpu_ref_resurrect(&p->users);
>>>>>> spin_lock(&swap_lock);
>>>>>> spin_lock(&p->lock);
>>>>>> _enable_swap_info(p);
>>>>>> @@ -2621,11 +2630,18 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
>>>>>> p->flags &= ~SWP_VALID; /* mark swap device as invalid */
>>>>>> spin_unlock(&p->lock);
>>>>>> spin_unlock(&swap_lock);
>>>>>> +
>>>>>> + percpu_ref_kill(&p->users);
>>>>>> /*
>>>>>> - * wait for swap operations protected by get/put_swap_device()
>>>>>> - * to complete
>>>>>> + * We need synchronize_rcu() here to protect the accessing
>>>>>> + * to the swap cache data structure.
>>>>>> */
>>>>>> synchronize_rcu();
>>>>>> + /*
>>>>>> + * Wait for swap operations protected by get/put_swap_device()
>>>>>> + * to complete.
>>>>>> + */
>>>>>
>>>>> I think the comments (after some revision) can be moved before
>>>>> percpu_ref_kill(). The synchronize_rcu() comments can be merged.
>>>>>
>>>>
>>>> Ok.
>>>>
>>>>>> + wait_for_completion(&p->comp);
>>>>>>
>>>>>> flush_work(&p->discard_work);
>>>>>>
>>>>>> @@ -3132,7 +3148,7 @@ static bool swap_discardable(struct swap_info_struct *si)
>>>>>> SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
>>>>>> {
>>>>>> struct swap_info_struct *p;
>>>>>> - struct filename *name;
>>>>>> + struct filename *name = NULL;
>>>>>> struct file *swap_file = NULL;
>>>>>> struct address_space *mapping;
>>>>>> int prio;
>>>>>> @@ -3163,6 +3179,15 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
>>>>>>
>>>>>> INIT_WORK(&p->discard_work, swap_discard_work);
>>>>>>
>>>>>> + if (!p->ref_initialized) {
>>>>>
>>>>> I don't think it's necessary to add another flag p->ref_initialized. We
>>>>> can distinguish newly allocated and reused swap_info_struct in alloc_swap_info().
>>>>>
>>>>
>>>> If newly allocated swap_info_struct failed to init percpu_ref, it will be considered as
>>>> a reused one in alloc_swap_info() _but_ the field users of swap_info_struct is actually
>>>> uninitialized. Does this make sense for you?
>>>
>>> We can call percpu_ref_init() just after kvzalloc() in alloc_swap_info().
>>>
>>
>> Yes, we can do it this way. But using ref_initialized might make the code more straightforward
>> and simple?
>
> I think that it's simpler to call percpu_ref_init() in
> alloc_swap_info(). We can just call percpu_ref_init() for allocated
> swap_info_struct blindly, and call percpu_ref_exit() if we reuse.
>
Looks good. Will do. Many thanks again.
> Best Regards,
> Huang, Ying
>
>>> Best Regards,
>>> Huang, Ying
>>>
>>>> Many Thanks for quick review.
>>>>
>>>>> Best Regards,
>>>>> Huang, Ying
>>>>>
>>>>>> + error = percpu_ref_init(&p->users, swap_users_ref_free,
>>>>>> + PERCPU_REF_INIT_DEAD, GFP_KERNEL);
>>>>>> + if (unlikely(error))
>>>>>> + goto bad_swap;
>>>>>> + init_completion(&p->comp);
>>>>>> + p->ref_initialized = true;
>>>>>> + }
>>>>>> +
>>>>>> name = getname(specialfile);
>>>>>> if (IS_ERR(name)) {
>>>>>> error = PTR_ERR(name);
>>>>> .
>>>>>
>>> .
>>>
> .
>
On 2021/4/19 15:09, Huang, Ying wrote:
> Miaohe Lin <[email protected]> writes:
>
>> On 2021/4/19 10:48, Huang, Ying wrote:
>>> Miaohe Lin <[email protected]> writes:
>>>
>>>> We will use percpu-refcount to serialize against concurrent swapoff. This
>>>> patch adds the percpu_ref support for swap.
>>>>
>>>> Signed-off-by: Miaohe Lin <[email protected]>
>>>> ---
>>>> include/linux/swap.h | 3 +++
>>>> mm/swapfile.c | 33 +++++++++++++++++++++++++++++----
>>>> 2 files changed, 32 insertions(+), 4 deletions(-)
>>>>
>>>> diff --git a/include/linux/swap.h b/include/linux/swap.h
>>>> index 144727041e78..8be36eb58b7a 100644
>>>> --- a/include/linux/swap.h
>>>> +++ b/include/linux/swap.h
>>>> @@ -240,6 +240,7 @@ struct swap_cluster_list {
>>>> * The in-memory structure used to track swap areas.
>>>> */
>>>> struct swap_info_struct {
>>>> + struct percpu_ref users; /* serialization against concurrent swapoff */
>>>
>>> The comments aren't general enough. We use this to check whether the
>>> swap device has been fully initialized, etc. May be something as below?
>>>
>>> /* indicate and keep swap device valid */
>>
>> Looks good.
>>
>>>
>>>> unsigned long flags; /* SWP_USED etc: see above */
>>>> signed short prio; /* swap priority of this type */
>>>> struct plist_node list; /* entry in swap_active_head */
>>>> @@ -260,6 +261,8 @@ struct swap_info_struct {
>>>> struct block_device *bdev; /* swap device or bdev of swap file */
>>>> struct file *swap_file; /* seldom referenced */
>>>> unsigned int old_block_size; /* seldom referenced */
>>>> + bool ref_initialized; /* seldom referenced */
>>>> + struct completion comp; /* seldom referenced */
>>>> #ifdef CONFIG_FRONTSWAP
>>>> unsigned long *frontswap_map; /* frontswap in-use, one bit per page */
>>>> atomic_t frontswap_pages; /* frontswap pages in-use counter */
>>>> diff --git a/mm/swapfile.c b/mm/swapfile.c
>>>> index 149e77454e3c..66515a3a2824 100644
>>>> --- a/mm/swapfile.c
>>>> +++ b/mm/swapfile.c
>>>> @@ -39,6 +39,7 @@
>>>> #include <linux/export.h>
>>>> #include <linux/swap_slots.h>
>>>> #include <linux/sort.h>
>>>> +#include <linux/completion.h>
>>>>
>>>> #include <asm/tlbflush.h>
>>>> #include <linux/swapops.h>
>>>> @@ -511,6 +512,14 @@ static void swap_discard_work(struct work_struct *work)
>>>> spin_unlock(&si->lock);
>>>> }
>>>>
>>>> +static void swap_users_ref_free(struct percpu_ref *ref)
>>>> +{
>>>> + struct swap_info_struct *si;
>>>> +
>>>> + si = container_of(ref, struct swap_info_struct, users);
>>>> + complete(&si->comp);
>>>> +}
>>>> +
>>>> static void alloc_cluster(struct swap_info_struct *si, unsigned long idx)
>>>> {
>>>> struct swap_cluster_info *ci = si->cluster_info;
>>>> @@ -2500,7 +2509,7 @@ static void enable_swap_info(struct swap_info_struct *p, int prio,
>>>> * Guarantee swap_map, cluster_info, etc. fields are valid
>>>> * between get/put_swap_device() if SWP_VALID bit is set
>>>> */
>>>> - synchronize_rcu();
>>>
>>> You cannot remove this without changing get/put_swap_device(). It's
>>> better to squash at least PATCH 1-2.
>>
>> Will squash PATCH 1-2. Thanks.
>>
>>>
>>>> + percpu_ref_resurrect(&p->users);
>>>> spin_lock(&swap_lock);
>>>> spin_lock(&p->lock);
>>>> _enable_swap_info(p);
>>>> @@ -2621,11 +2630,18 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
>>>> p->flags &= ~SWP_VALID; /* mark swap device as invalid */
>>>> spin_unlock(&p->lock);
>>>> spin_unlock(&swap_lock);
>>>> +
>>>> + percpu_ref_kill(&p->users);
>>>> /*
>>>> - * wait for swap operations protected by get/put_swap_device()
>>>> - * to complete
>>>> + * We need synchronize_rcu() here to protect the accessing
>>>> + * to the swap cache data structure.
>>>> */
>>>> synchronize_rcu();
>>>> + /*
>>>> + * Wait for swap operations protected by get/put_swap_device()
>>>> + * to complete.
>>>> + */
>>>
>>> I think the comments (after some revision) can be moved before
>>> percpu_ref_kill(). The synchronize_rcu() comments can be merged.
>>>
>>
>> Ok.
>>
>>>> + wait_for_completion(&p->comp);
>>>>
>>>> flush_work(&p->discard_work);
>>>>
>>>> @@ -3132,7 +3148,7 @@ static bool swap_discardable(struct swap_info_struct *si)
>>>> SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
>>>> {
>>>> struct swap_info_struct *p;
>>>> - struct filename *name;
>>>> + struct filename *name = NULL;
>>>> struct file *swap_file = NULL;
>>>> struct address_space *mapping;
>>>> int prio;
>>>> @@ -3163,6 +3179,15 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
>>>>
>>>> INIT_WORK(&p->discard_work, swap_discard_work);
>>>>
>>>> + if (!p->ref_initialized) {
>>>
>>> I don't think it's necessary to add another flag p->ref_initialized. We
>>> can distinguish newly allocated and reused swap_info_struct in alloc_swap_info().
>>>
>>
>> If newly allocated swap_info_struct failed to init percpu_ref, it will be considered as
>> a reused one in alloc_swap_info() _but_ the field users of swap_info_struct is actually
>> uninitialized. Does this make sense for you?
>
> We can call percpu_ref_init() just after kvzalloc() in alloc_swap_info().
>
Yes, we can do it this way. But using ref_initialized might make the code more straightforward
and simple?
> Best Regards,
> Huang, Ying
>
>> Many Thanks for quick review.
>>
>>> Best Regards,
>>> Huang, Ying
>>>
>>>> + error = percpu_ref_init(&p->users, swap_users_ref_free,
>>>> + PERCPU_REF_INIT_DEAD, GFP_KERNEL);
>>>> + if (unlikely(error))
>>>> + goto bad_swap;
>>>> + init_completion(&p->comp);
>>>> + p->ref_initialized = true;
>>>> + }
>>>> +
>>>> name = getname(specialfile);
>>>> if (IS_ERR(name)) {
>>>> error = PTR_ERR(name);
>>> .
>>>
> .
>
Miaohe Lin <[email protected]> writes:
> On 2021/4/19 15:09, Huang, Ying wrote:
>> Miaohe Lin <[email protected]> writes:
>>
>>> On 2021/4/19 10:48, Huang, Ying wrote:
>>>> Miaohe Lin <[email protected]> writes:
>>>>
>>>>> We will use percpu-refcount to serialize against concurrent swapoff. This
>>>>> patch adds the percpu_ref support for swap.
>>>>>
>>>>> Signed-off-by: Miaohe Lin <[email protected]>
>>>>> ---
>>>>> include/linux/swap.h | 3 +++
>>>>> mm/swapfile.c | 33 +++++++++++++++++++++++++++++----
>>>>> 2 files changed, 32 insertions(+), 4 deletions(-)
>>>>>
>>>>> diff --git a/include/linux/swap.h b/include/linux/swap.h
>>>>> index 144727041e78..8be36eb58b7a 100644
>>>>> --- a/include/linux/swap.h
>>>>> +++ b/include/linux/swap.h
>>>>> @@ -240,6 +240,7 @@ struct swap_cluster_list {
>>>>> * The in-memory structure used to track swap areas.
>>>>> */
>>>>> struct swap_info_struct {
>>>>> + struct percpu_ref users; /* serialization against concurrent swapoff */
>>>>
>>>> The comments aren't general enough. We use this to check whether the
>>>> swap device has been fully initialized, etc. May be something as below?
>>>>
>>>> /* indicate and keep swap device valid */
>>>
>>> Looks good.
>>>
>>>>
>>>>> unsigned long flags; /* SWP_USED etc: see above */
>>>>> signed short prio; /* swap priority of this type */
>>>>> struct plist_node list; /* entry in swap_active_head */
>>>>> @@ -260,6 +261,8 @@ struct swap_info_struct {
>>>>> struct block_device *bdev; /* swap device or bdev of swap file */
>>>>> struct file *swap_file; /* seldom referenced */
>>>>> unsigned int old_block_size; /* seldom referenced */
>>>>> + bool ref_initialized; /* seldom referenced */
>>>>> + struct completion comp; /* seldom referenced */
>>>>> #ifdef CONFIG_FRONTSWAP
>>>>> unsigned long *frontswap_map; /* frontswap in-use, one bit per page */
>>>>> atomic_t frontswap_pages; /* frontswap pages in-use counter */
>>>>> diff --git a/mm/swapfile.c b/mm/swapfile.c
>>>>> index 149e77454e3c..66515a3a2824 100644
>>>>> --- a/mm/swapfile.c
>>>>> +++ b/mm/swapfile.c
>>>>> @@ -39,6 +39,7 @@
>>>>> #include <linux/export.h>
>>>>> #include <linux/swap_slots.h>
>>>>> #include <linux/sort.h>
>>>>> +#include <linux/completion.h>
>>>>>
>>>>> #include <asm/tlbflush.h>
>>>>> #include <linux/swapops.h>
>>>>> @@ -511,6 +512,14 @@ static void swap_discard_work(struct work_struct *work)
>>>>> spin_unlock(&si->lock);
>>>>> }
>>>>>
>>>>> +static void swap_users_ref_free(struct percpu_ref *ref)
>>>>> +{
>>>>> + struct swap_info_struct *si;
>>>>> +
>>>>> + si = container_of(ref, struct swap_info_struct, users);
>>>>> + complete(&si->comp);
>>>>> +}
>>>>> +
>>>>> static void alloc_cluster(struct swap_info_struct *si, unsigned long idx)
>>>>> {
>>>>> struct swap_cluster_info *ci = si->cluster_info;
>>>>> @@ -2500,7 +2509,7 @@ static void enable_swap_info(struct swap_info_struct *p, int prio,
>>>>> * Guarantee swap_map, cluster_info, etc. fields are valid
>>>>> * between get/put_swap_device() if SWP_VALID bit is set
>>>>> */
>>>>> - synchronize_rcu();
>>>>
>>>> You cannot remove this without changing get/put_swap_device(). It's
>>>> better to squash at least PATCH 1-2.
>>>
>>> Will squash PATCH 1-2. Thanks.
>>>
>>>>
>>>>> + percpu_ref_resurrect(&p->users);
>>>>> spin_lock(&swap_lock);
>>>>> spin_lock(&p->lock);
>>>>> _enable_swap_info(p);
>>>>> @@ -2621,11 +2630,18 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
>>>>> p->flags &= ~SWP_VALID; /* mark swap device as invalid */
>>>>> spin_unlock(&p->lock);
>>>>> spin_unlock(&swap_lock);
>>>>> +
>>>>> + percpu_ref_kill(&p->users);
>>>>> /*
>>>>> - * wait for swap operations protected by get/put_swap_device()
>>>>> - * to complete
>>>>> + * We need synchronize_rcu() here to protect the accessing
>>>>> + * to the swap cache data structure.
>>>>> */
>>>>> synchronize_rcu();
>>>>> + /*
>>>>> + * Wait for swap operations protected by get/put_swap_device()
>>>>> + * to complete.
>>>>> + */
>>>>
>>>> I think the comments (after some revision) can be moved before
>>>> percpu_ref_kill(). The synchronize_rcu() comments can be merged.
>>>>
>>>
>>> Ok.
>>>
>>>>> + wait_for_completion(&p->comp);
>>>>>
>>>>> flush_work(&p->discard_work);
>>>>>
>>>>> @@ -3132,7 +3148,7 @@ static bool swap_discardable(struct swap_info_struct *si)
>>>>> SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
>>>>> {
>>>>> struct swap_info_struct *p;
>>>>> - struct filename *name;
>>>>> + struct filename *name = NULL;
>>>>> struct file *swap_file = NULL;
>>>>> struct address_space *mapping;
>>>>> int prio;
>>>>> @@ -3163,6 +3179,15 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
>>>>>
>>>>> INIT_WORK(&p->discard_work, swap_discard_work);
>>>>>
>>>>> + if (!p->ref_initialized) {
>>>>
>>>> I don't think it's necessary to add another flag p->ref_initialized. We
>>>> can distinguish newly allocated and reused swap_info_struct in alloc_swap_info().
>>>>
>>>
>>> If newly allocated swap_info_struct failed to init percpu_ref, it will be considered as
>>> a reused one in alloc_swap_info() _but_ the field users of swap_info_struct is actually
>>> uninitialized. Does this make sense for you?
>>
>> We can call percpu_ref_init() just after kvzalloc() in alloc_swap_info().
>>
>
> Yes, we can do it this way. But using ref_initialized might make the code more straightforward
> and simple?
I think that it's simpler to call percpu_ref_init() in
alloc_swap_info(). We can just call percpu_ref_init() for allocated
swap_info_struct blindly, and call percpu_ref_exit() if we reuse.
Best Regards,
Huang, Ying
>> Best Regards,
>> Huang, Ying
>>
>>> Many Thanks for quick review.
>>>
>>>> Best Regards,
>>>> Huang, Ying
>>>>
>>>>> + error = percpu_ref_init(&p->users, swap_users_ref_free,
>>>>> + PERCPU_REF_INIT_DEAD, GFP_KERNEL);
>>>>> + if (unlikely(error))
>>>>> + goto bad_swap;
>>>>> + init_completion(&p->comp);
>>>>> + p->ref_initialized = true;
>>>>> + }
>>>>> +
>>>>> name = getname(specialfile);
>>>>> if (IS_ERR(name)) {
>>>>> error = PTR_ERR(name);
>>>> .
>>>>
>> .
>>