I was wrong, openVz blocks sys_swapon/swapoff syscalls inside containers.
Our kernel just emulates /proc/swaps output inside containers,
it is enough for 'swapon' userspace to do not fail and show required info.
So I do not have any special arguments for proposed patch.
On 11/5/18 8:19 AM, Vasily Averin wrote:
> 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;
>>> /*
>>
