Vasily Averin <v...@virtuozzo.com> writes:
> On 11/5/18 3:50 AM, Huang, Ying wrote:
>> Vasily Averin <v...@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
