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 <[email protected]> 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 <[email protected]> >>> --- >>> 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; >>> /* >>
