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; >> /* >
