On Thu 15-11-18 16:38:47, Aaron Lu wrote:
> Since commit a2468cc9bfdf ("swap: choose swap device according to
> numa node"), avail_lists field of swap_info_struct is changed to
> an array with MAX_NUMNODES elements. This made swap_info_struct
> size increased to 40KiB and needs an order-4 page to hold it.
>
> This is not optimal in that:
> 1 Most systems have way less than MAX_NUMNODES(1024) nodes so it
> is a waste of memory;
> 2 It could cause swapon failure if the swap device is swapped on
> after system has been running for a while, due to no order-4
> page is available as pointed out by Vasily Averin.
>
> Solve the above two issues by using nr_node_ids(which is the actual
> possible node number the running system has) for avail_lists instead
> of MAX_NUMNODES.
>
> nr_node_ids is unknown at compile time so can't be directly used
> when declaring this array. What I did here is to declare avail_lists
> as zero element array and allocate space for it when allocating
> space for swap_info_struct. The reason why keep using array but
> not pointer is plist_for_each_entry needs the field to be part
> of the struct, so pointer will not work.
>
> This patch is on top of Vasily Averin's fix commit. I think the
> use of kvzalloc for swap_info_struct is still needed in case
> nr_node_ids is really big on some systems.
I haven't seen any system with a huge nr_node_ids but using kvzalloc
is not harmfull.
> Cc: Vasily Averin <vvs@xxxxxxxxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxxx>
> Cc: Huang Ying <ying.huang@xxxxxxxxx>
> Signed-off-by: Aaron Lu <aaron.lu@xxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
> ---
> include/linux/swap.h | 11 ++++++++++-
> mm/swapfile.c | 3 ++-
> 2 files changed, 12 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/swap.h b/include/linux/swap.h
> index d8a07a4f171d..3d3630b3f63d 100644
> --- a/include/linux/swap.h
> +++ b/include/linux/swap.h
> @@ -233,7 +233,6 @@ struct swap_info_struct {
> unsigned long flags; /* SWP_USED etc: see above */
> signed short prio; /* swap priority of this type */
> struct plist_node list; /* entry in swap_active_head */
> - struct plist_node avail_lists[MAX_NUMNODES];/* entry in swap_avail_heads */
> signed char type; /* strange name for an index */
> unsigned int max; /* extent of the swap_map */
> unsigned char *swap_map; /* vmalloc'ed array of usage counts */
> @@ -274,6 +273,16 @@ struct swap_info_struct {
> */
> struct work_struct discard_work; /* discard worker */
> struct swap_cluster_list discard_clusters; /* discard clusters list */
> + struct plist_node avail_lists[0]; /*
> + * entries in swap_avail_heads, one
> + * entry per node.
> + * Must be last as the number of the
> + * array is nr_node_ids, which is not
> + * a fixed value so have to allocate
> + * dynamically.
> + * And it has to be an array so that
> + * plist_for_each_* can work.
> + */
> };
>
> #ifdef CONFIG_64BIT
> diff --git a/mm/swapfile.c b/mm/swapfile.c
> index 8688ae65ef58..6e06821623f6 100644
> --- a/mm/swapfile.c
> +++ b/mm/swapfile.c
> @@ -2812,8 +2812,9 @@ static struct swap_info_struct *alloc_swap_info(void)
> struct swap_info_struct *p;
> unsigned int type;
> int i;
> + int size = sizeof(*p) + nr_node_ids * sizeof(struct plist_node);
>
> - p = kvzalloc(sizeof(*p), GFP_KERNEL);
> + p = kvzalloc(size, GFP_KERNEL);
> if (!p)
> return ERR_PTR(-ENOMEM);
>
> --
> 2.17.2
>
--
Michal Hocko
SUSE Labs
