| Message ID | 37b60523-d085-71e9-fef9-80b90bfcef18@virtuozzo.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [1/2] mm: use kvzalloc for swap_info_struct allocation | expand |
Vasily Averin <vvs@virtuozzo.com> 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 <vvs@virtuozzo.com> > --- > 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 <vvs@virtuozzo.com> 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 <vvs@virtuozzo.com> writes: > On 11/5/18 3:50 AM, Huang, Ying wrote: >> Vasily Averin <vvs@virtuozzo.com> 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 <vvs@virtuozzo.com> 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 <aaron.lu@intel.com> 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 >
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()
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 <vvs@virtuozzo.com> --- mm/swapfile.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)