On 11/5/18 3:57 AM, Huang, Ying wrote:
> Vasily Averin <vvs@xxxxxxxxxxxxx> writes:
>
>> Currently newly allocated swap_info_struct can be quickly freed.
>> This patch avoid uneccessary high-order page allocation and helps
>> to decrease the memory pressure.
>
> I think swapon/swapoff are rare operations, so it will not increase the
> memory pressure much.
You are right, typically it should not affect usual nodes.
It's OpenVz-specific usecase.
OpenVz allows hosters to run hundreds of non-trusted containers per node.
Our containers have enabled "virtual swap" functionality,
and container's owners can call sys_swapon without any limits.
Containers can be restarted in any time and we would like to
decrease number of unnecessary high-order memory allocations.
>> Signed-off-by: Vasily Averin <vvs@xxxxxxxxxxxxx>
>> ---
>> mm/swapfile.c | 18 +++++++++++++-----
>> 1 file changed, 13 insertions(+), 5 deletions(-)
>>
>> diff --git a/mm/swapfile.c b/mm/swapfile.c
>> index 8688ae65ef58..53ec2f0cdf26 100644
>> --- a/mm/swapfile.c
>> +++ b/mm/swapfile.c
>> @@ -2809,14 +2809,17 @@ late_initcall(max_swapfiles_check);
>>
>> static struct swap_info_struct *alloc_swap_info(void)
>> {
>> - struct swap_info_struct *p;
>> + struct swap_info_struct *p = NULL;
>> unsigned int type;
>> int i;
>> + bool force_alloc = false;
>>
>> - p = kvzalloc(sizeof(*p), GFP_KERNEL);
>> - if (!p)
>> - return ERR_PTR(-ENOMEM);
>> -
>> +retry:
>> + if (force_alloc) {
>> + p = kvzalloc(sizeof(*p), GFP_KERNEL);
>> + if (!p)
>> + return ERR_PTR(-ENOMEM);
>> + }
>> spin_lock(&swap_lock);
>> for (type = 0; type < nr_swapfiles; type++) {
>> if (!(swap_info[type]->flags & SWP_USED))
>> @@ -2828,6 +2831,11 @@ static struct swap_info_struct *alloc_swap_info(void)
>> return ERR_PTR(-EPERM);
>> }
>> if (type >= nr_swapfiles) {
>> + if (!force_alloc) {
>> + force_alloc = true;
>> + spin_unlock(&swap_lock);
>> + goto retry;
>> + }
>> p->type = type;
>> swap_info[type] = p;
>> /*
>
