commit a2468cc9bfdf ("swap: choose swap device according to numa node")
increased size of swap_info_struct up to 44 Kbytes, now it requires 4th order page.
Switch to kvzmalloc allows to avoid unexpected allocation failures.
Signed-off-by: Vasily Averin <[email protected]>
---
mm/swapfile.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 644f746e167a..8688ae65ef58 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -2813,7 +2813,7 @@ static struct swap_info_struct *alloc_swap_info(void)
unsigned int type;
int i;
- p = kzalloc(sizeof(*p), GFP_KERNEL);
+ p = kvzalloc(sizeof(*p), GFP_KERNEL);
if (!p)
return ERR_PTR(-ENOMEM);
@@ -2824,7 +2824,7 @@ static struct swap_info_struct *alloc_swap_info(void)
}
if (type >= MAX_SWAPFILES) {
spin_unlock(&swap_lock);
- kfree(p);
+ kvfree(p);
return ERR_PTR(-EPERM);
}
if (type >= nr_swapfiles) {
@@ -2838,7 +2838,7 @@ static struct swap_info_struct *alloc_swap_info(void)
smp_wmb();
nr_swapfiles++;
} else {
- kfree(p);
+ kvfree(p);
p = swap_info[type];
/*
* Do not memset this entry: a racing procfs swap_next()
--
2.17.1
Vasily Averin <[email protected]> writes:
> commit a2468cc9bfdf ("swap: choose swap device according to numa node")
> increased size of swap_info_struct up to 44 Kbytes, now it requires
> 4th order page.
Why swap_info_struct could be so large? Because MAX_NUMNODES could be
thousands so that 'avail_lists' field could be tens KB? If so, I think
it's fair to use kvzalloc(). Can you add one line comment? Because
struct swap_info_struct is quite small in default configuration.
Best Regards,
Huang, Ying
> Switch to kvzmalloc allows to avoid unexpected allocation failures.
>
> Signed-off-by: Vasily Averin <[email protected]>
> ---
> mm/swapfile.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/mm/swapfile.c b/mm/swapfile.c
> index 644f746e167a..8688ae65ef58 100644
> --- a/mm/swapfile.c
> +++ b/mm/swapfile.c
> @@ -2813,7 +2813,7 @@ static struct swap_info_struct *alloc_swap_info(void)
> unsigned int type;
> int i;
>
> - p = kzalloc(sizeof(*p), GFP_KERNEL);
> + p = kvzalloc(sizeof(*p), GFP_KERNEL);
> if (!p)
> return ERR_PTR(-ENOMEM);
>
> @@ -2824,7 +2824,7 @@ static struct swap_info_struct *alloc_swap_info(void)
> }
> if (type >= MAX_SWAPFILES) {
> spin_unlock(&swap_lock);
> - kfree(p);
> + kvfree(p);
> return ERR_PTR(-EPERM);
> }
> if (type >= nr_swapfiles) {
> @@ -2838,7 +2838,7 @@ static struct swap_info_struct *alloc_swap_info(void)
> smp_wmb();
> nr_swapfiles++;
> } else {
> - kfree(p);
> + kvfree(p);
> p = swap_info[type];
> /*
> * Do not memset this entry: a racing procfs swap_next()
On 11/5/18 3:50 AM, Huang, Ying wrote:
> Vasily Averin <[email protected]> writes:
>
>> commit a2468cc9bfdf ("swap: choose swap device according to numa node")
>> increased size of swap_info_struct up to 44 Kbytes, now it requires
>> 4th order page.
>
> Why swap_info_struct could be so large? Because MAX_NUMNODES could be
> thousands so that 'avail_lists' field could be tens KB? If so, I think
> it's fair to use kvzalloc(). Can you add one line comment? Because
> struct swap_info_struct is quite small in default configuration.
I was incorrect not 44Kb but 40kb should be here.
We have found CONFIG_NODES_SHIFT=10 in new RHEL7 update 6 kernel,
default ubuntu kernels have the same setting too.
crash> struct swap_info_struct -o
struct swap_info_struct {
[0] unsigned long flags;
[8] short prio;
...
[140] spinlock_t lock;
[144] struct plist_node list;
[184] struct plist_node avail_lists[1024]; <<<< here
[41144] struct swap_cluster_info *cluster_info;
[41152] struct swap_cluster_list free_clusters;
...
[41224] spinlock_t cont_lock;
}
SIZE: 41232
struct swap_info_struct {
...
RH_KABI_EXTEND(struct plist_node avail_lists[MAX_NUMNODES]) /* entry in swap_avail_head */
...
}
#define MAX_NUMNODES (1 << NODES_SHIFT)
#ifdef CONFIG_NODES_SHIFT
#define NODES_SHIFT CONFIG_NODES_SHIFT
#else
#define NODES_SHIFT 0
#endif
/boot/config-4.15.0-38-generic:CONFIG_NODES_SHIFT=10
Vasily Averin <[email protected]> writes:
> On 11/5/18 3:50 AM, Huang, Ying wrote:
>> Vasily Averin <[email protected]> writes:
>>
>>> commit a2468cc9bfdf ("swap: choose swap device according to numa node")
>>> increased size of swap_info_struct up to 44 Kbytes, now it requires
>>> 4th order page.
>>
>> Why swap_info_struct could be so large? Because MAX_NUMNODES could be
>> thousands so that 'avail_lists' field could be tens KB? If so, I think
>> it's fair to use kvzalloc(). Can you add one line comment? Because
>> struct swap_info_struct is quite small in default configuration.
>
> I was incorrect not 44Kb but 40kb should be here.
> We have found CONFIG_NODES_SHIFT=10 in new RHEL7 update 6 kernel,
> default ubuntu kernels have the same setting too.
>
> crash> struct swap_info_struct -o
> struct swap_info_struct {
> [0] unsigned long flags;
> [8] short prio;
> ...
> [140] spinlock_t lock;
> [144] struct plist_node list;
> [184] struct plist_node avail_lists[1024]; <<<< here
> [41144] struct swap_cluster_info *cluster_info;
> [41152] struct swap_cluster_list free_clusters;
> ...
> [41224] spinlock_t cont_lock;
> }
> SIZE: 41232
>
> struct swap_info_struct {
> ...
> RH_KABI_EXTEND(struct plist_node avail_lists[MAX_NUMNODES]) /* entry in swap_avail_head */
> ...
> }
>
> #define MAX_NUMNODES (1 << NODES_SHIFT)
>
> #ifdef CONFIG_NODES_SHIFT
> #define NODES_SHIFT CONFIG_NODES_SHIFT
> #else
> #define NODES_SHIFT 0
> #endif
>
> /boot/config-4.15.0-38-generic:CONFIG_NODES_SHIFT=10
I see. So this is a more practical issue than my original imagination.
But for default config, I mean
$ make defconfig
And it turns out,
CONFIG_NODES_SHIFT=6
Best Regards,
Huang, Ying
On Mon, Nov 05, 2018 at 07:59:13AM +0300, Vasily Averin wrote:
>
>
> On 11/5/18 3:50 AM, Huang, Ying wrote:
> > Vasily Averin <[email protected]> writes:
> >
> >> commit a2468cc9bfdf ("swap: choose swap device according to numa node")
> >> increased size of swap_info_struct up to 44 Kbytes, now it requires
> >> 4th order page.
> >
> > Why swap_info_struct could be so large? Because MAX_NUMNODES could be
> > thousands so that 'avail_lists' field could be tens KB? If so, I think
> > it's fair to use kvzalloc(). Can you add one line comment? Because
> > struct swap_info_struct is quite small in default configuration.
>
> I was incorrect not 44Kb but 40kb should be here.
> We have found CONFIG_NODES_SHIFT=10 in new RHEL7 update 6 kernel,
> default ubuntu kernels have the same setting too.
>
> crash> struct swap_info_struct -o
> struct swap_info_struct {
> [0] unsigned long flags;
> [8] short prio;
> ...
> [140] spinlock_t lock;
> [144] struct plist_node list;
> [184] struct plist_node avail_lists[1024]; <<<< here
So every 'struct plist_node' takes 40 bytes and 1024 of them take a
total of 40960 bytes, which is 10 pages and need an order-4 page to host
them. It looks a little too much, especially consider most of the space
will left be unused since most systems have nodes <= 4. I didn't realize
this problem when developing this patch, thanks for pointing this out.
I think using kvzalloc() as is done by your patch is better here as it
can avoid possible failure of swapon.
Acked-by: Aaron Lu <[email protected]>
BTW, for systems with few swap devices this may not be a big deal, but
according to your description, your workload will create a lot of swap
devices and each of them will likely cause an order-4 unmovable pages
allocated(when kvzalloc() doesn't fallback). I was thinking maybe we
should convert avail_lists to a pointer in swap_info_struct and use
vzalloc() for it.
Thanks,
Aaron
> [41144] struct swap_cluster_info *cluster_info;
> [41152] struct swap_cluster_list free_clusters;
> ...
> [41224] spinlock_t cont_lock;
> }
> SIZE: 41232
>
> struct swap_info_struct {
> ...
> RH_KABI_EXTEND(struct plist_node avail_lists[MAX_NUMNODES]) /* entry in swap_avail_head */
> ...
> }
>
> #define MAX_NUMNODES (1 << NODES_SHIFT)
>
> #ifdef CONFIG_NODES_SHIFT
> #define NODES_SHIFT CONFIG_NODES_SHIFT
> #else
> #define NODES_SHIFT 0
> #endif
>
> /boot/config-4.15.0-38-generic:CONFIG_NODES_SHIFT=10
>
commit a2468cc9bfdf ("swap: choose swap device according to numa node")
changed 'avail_lists' field of 'struct swap_info_struct' to an array.
In popular linux distros it increased size of swap_info_struct up to
40 Kbytes and now swap_info_struct allocation requires order-4 page.
Switch to kvzmalloc allows to avoid unexpected allocation failures.
Acked-by: Aaron Lu <[email protected]>
Signed-off-by: Vasily Averin <[email protected]>
---
mm/swapfile.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 644f746e167a..8688ae65ef58 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -2813,7 +2813,7 @@ static struct swap_info_struct *alloc_swap_info(void)
unsigned int type;
int i;
- p = kzalloc(sizeof(*p), GFP_KERNEL);
+ p = kvzalloc(sizeof(*p), GFP_KERNEL);
if (!p)
return ERR_PTR(-ENOMEM);
@@ -2824,7 +2824,7 @@ static struct swap_info_struct *alloc_swap_info(void)
}
if (type >= MAX_SWAPFILES) {
spin_unlock(&swap_lock);
- kfree(p);
+ kvfree(p);
return ERR_PTR(-EPERM);
}
if (type >= nr_swapfiles) {
@@ -2838,7 +2838,7 @@ static struct swap_info_struct *alloc_swap_info(void)
smp_wmb();
nr_swapfiles++;
} else {
- kfree(p);
+ kvfree(p);
p = swap_info[type];
/*
* Do not memset this entry: a racing procfs swap_next()
--
2.17.1
On Mon 05-11-18 14:17:01, Vasily Averin wrote:
> commit a2468cc9bfdf ("swap: choose swap device according to numa node")
> changed 'avail_lists' field of 'struct swap_info_struct' to an array.
> In popular linux distros it increased size of swap_info_struct up to
> 40 Kbytes and now swap_info_struct allocation requires order-4 page.
> Switch to kvzmalloc allows to avoid unexpected allocation failures.
While this fixes the most visible issue is this a good long term
solution? Aren't we wasting memory without a good reason? IIRC our limit
for swap files/devices is much smaller than potential NUMA nodes numbers
so we can safely expect that would be only few numa affine nodes. I am
not really familiar with the rework which has added numa node awareness
but I wouls assueme that we should either go with one global table with
a linked list of possible swap_info structure per numa node or use a
sparse array.
That being said I am not really objecting to this patch as it is simple
and backportable to older (stable kernels).
I would even dare to add
Fixes: a2468cc9bfdf ("swap: choose swap device according to numa node")
because not being able to add a swap space on a fragmented system looks
like a regression to me.
> Acked-by: Aaron Lu <[email protected]>
> Signed-off-by: Vasily Averin <[email protected]>
Acked-by: Michal Hocko <[email protected]>
> ---
> mm/swapfile.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/mm/swapfile.c b/mm/swapfile.c
> index 644f746e167a..8688ae65ef58 100644
> --- a/mm/swapfile.c
> +++ b/mm/swapfile.c
> @@ -2813,7 +2813,7 @@ static struct swap_info_struct *alloc_swap_info(void)
> unsigned int type;
> int i;
>
> - p = kzalloc(sizeof(*p), GFP_KERNEL);
> + p = kvzalloc(sizeof(*p), GFP_KERNEL);
> if (!p)
> return ERR_PTR(-ENOMEM);
>
> @@ -2824,7 +2824,7 @@ static struct swap_info_struct *alloc_swap_info(void)
> }
> if (type >= MAX_SWAPFILES) {
> spin_unlock(&swap_lock);
> - kfree(p);
> + kvfree(p);
> return ERR_PTR(-EPERM);
> }
> if (type >= nr_swapfiles) {
> @@ -2838,7 +2838,7 @@ static struct swap_info_struct *alloc_swap_info(void)
> smp_wmb();
> nr_swapfiles++;
> } else {
> - kfree(p);
> + kvfree(p);
> p = swap_info[type];
> /*
> * Do not memset this entry: a racing procfs swap_next()
> --
> 2.17.1
--
Michal Hocko
SUSE Labs
On Mon, Nov 05, 2018 at 03:11:56PM +0100, Michal Hocko wrote:
> On Mon 05-11-18 14:17:01, Vasily Averin wrote:
> > commit a2468cc9bfdf ("swap: choose swap device according to numa node")
> > changed 'avail_lists' field of 'struct swap_info_struct' to an array.
> > In popular linux distros it increased size of swap_info_struct up to
> > 40 Kbytes and now swap_info_struct allocation requires order-4 page.
> > Switch to kvzmalloc allows to avoid unexpected allocation failures.
>
> While this fixes the most visible issue is this a good long term
> solution? Aren't we wasting memory without a good reason? IIRC our limit
That's right, we need a better way of handling this in the long term.
> for swap files/devices is much smaller than potential NUMA nodes numbers
> so we can safely expect that would be only few numa affine nodes. I am
> not really familiar with the rework which has added numa node awareness
> but I wouls assueme that we should either go with one global table with
> a linked list of possible swap_info structure per numa node or use a
> sparse array.
There is a per-numa-node plist of available swap devices, so every swap
device needs an entry on those per-numa-node plist.
I think we can convert avail_lists from array to pointer and use vzalloc
to allocate the needed memory. MAX_NUMANODES can be used for a simple
implementation, or use the precise online node number but then we will
need to handle node online/offline events.
sparse array sounds promising, I'll take a look, thanks for the pointer.
> That being said I am not really objecting to this patch as it is simple
> and backportable to older (stable kernels).
>
> I would even dare to add
> Fixes: a2468cc9bfdf ("swap: choose swap device according to numa node")
>
> because not being able to add a swap space on a fragmented system looks
> like a regression to me.
Agree, especially it used to work.
Regards,
Aaron
> > Acked-by: Aaron Lu <[email protected]>
> > Signed-off-by: Vasily Averin <[email protected]>
>
> Acked-by: Michal Hocko <[email protected]>
> > ---
> > mm/swapfile.c | 6 +++---
> > 1 file changed, 3 insertions(+), 3 deletions(-)
> >
> > diff --git a/mm/swapfile.c b/mm/swapfile.c
> > index 644f746e167a..8688ae65ef58 100644
> > --- a/mm/swapfile.c
> > +++ b/mm/swapfile.c
> > @@ -2813,7 +2813,7 @@ static struct swap_info_struct *alloc_swap_info(void)
> > unsigned int type;
> > int i;
> >
> > - p = kzalloc(sizeof(*p), GFP_KERNEL);
> > + p = kvzalloc(sizeof(*p), GFP_KERNEL);
> > if (!p)
> > return ERR_PTR(-ENOMEM);
> >
> > @@ -2824,7 +2824,7 @@ static struct swap_info_struct *alloc_swap_info(void)
> > }
> > if (type >= MAX_SWAPFILES) {
> > spin_unlock(&swap_lock);
> > - kfree(p);
> > + kvfree(p);
> > return ERR_PTR(-EPERM);
> > }
> > if (type >= nr_swapfiles) {
> > @@ -2838,7 +2838,7 @@ static struct swap_info_struct *alloc_swap_info(void)
> > smp_wmb();
> > nr_swapfiles++;
> > } else {
> > - kfree(p);
> > + kvfree(p);
> > p = swap_info[type];
> > /*
> > * Do not memset this entry: a racing procfs swap_next()
> > --
> > 2.17.1
>
> --
> Michal Hocko
> SUSE Labs
>