On Fri, 10 Feb 2023 09:18:52 +0800 (CST)
<yang.yang29@xxxxxxxxxx> wrote:
> From: xu xin <xu.xin16@xxxxxxxxxx>
>
> As pages_sharing and pages_shared don't include the number of zero pages
> merged by KSM, we cannot know how many pages are zero pages placed by KSM
> when enabling use_zero_pages, which leads to KSM not being transparent with
> all actual merged pages by KSM. In the early days of use_zero_pages,
> zero-pages was unable to get unshared by the ways like MADV_UNMERGEABLE so
> it's hard to count how many times one of those zeropages was then unmerged.
>
> But now, unsharing KSM-placed zero page accurately has been achieved, so we
> can easily count both how many times a page full of zeroes was merged with
> zero-page and how many times one of those pages was then unmerged. and so,
> it helps to estimate memory demands when each and every shared page could
> get unshared.
>
> So we add zero_pages_sharing under /sys/kernel/mm/ksm/ to show the number
> of all zero pages placed by KSM.
>
> Signed-off-by: xu xin <xu.xin16@xxxxxxxxxx>
> Cc: Claudio Imbrenda <imbrenda@xxxxxxxxxxxxx>
> Cc: David Hildenbrand <david@xxxxxxxxxx>
> Cc: Xuexin Jiang <jiang.xuexin@xxxxxxxxxx>
> Reviewed-by: Xiaokai Ran <ran.xiaokai@xxxxxxxxxx>
> Reviewed-by: Yang Yang <yang.yang29@xxxxxxxxxx>
Reviewed-by: Claudio Imbrenda <imbrenda@xxxxxxxxxxxxx>
>
> v4->v5:
> fix warning mm/ksm.c:3238:9: warning: no previous prototype for
> 'zero_pages_sharing_show' [-Wmissing-prototypes].
> ---
> mm/ksm.c | 19 +++++++++++++++++--
> 1 file changed, 17 insertions(+), 2 deletions(-)
>
> diff --git a/mm/ksm.c b/mm/ksm.c
> index ab04b44679c8..1fa668e1fe82 100644
> --- a/mm/ksm.c
> +++ b/mm/ksm.c
> @@ -276,6 +276,9 @@ static unsigned int zero_checksum __read_mostly;
> /* Whether to merge empty (zeroed) pages with actual zero pages */
> static bool ksm_use_zero_pages __read_mostly;
>
> +/* The number of zero pages placed by KSM use_zero_pages */
> +static unsigned long ksm_zero_pages_sharing;
> +
> #ifdef CONFIG_NUMA
> /* Zeroed when merging across nodes is not allowed */
> static unsigned int ksm_merge_across_nodes = 1;
> @@ -789,8 +792,10 @@ static struct page *get_ksm_page(struct ksm_stable_node *stable_node,
> */
> static inline void clean_rmap_item_zero_flag(struct ksm_rmap_item *rmap_item)
> {
> - if (rmap_item->address & ZERO_PAGE_FLAG)
> + if (rmap_item->address & ZERO_PAGE_FLAG) {
> + ksm_zero_pages_sharing--;
> rmap_item->address &= PAGE_MASK;
> + }
> }
>
> /* Only called when rmap_item is going to be freed */
> @@ -2109,8 +2114,10 @@ static int try_to_merge_with_kernel_zero_page(struct ksm_rmap_item *rmap_item,
> if (vma) {
> err = try_to_merge_one_page(vma, page,
> ZERO_PAGE(rmap_item->address));
> - if (!err)
> + if (!err) {
> rmap_item->address |= ZERO_PAGE_FLAG;
> + ksm_zero_pages_sharing++;
> + }
> } else {
> /* If the vma is out of date, we do not need to continue. */
> err = 0;
> @@ -3230,6 +3237,13 @@ static ssize_t pages_volatile_show(struct kobject *kobj,
> }
> KSM_ATTR_RO(pages_volatile);
>
> +static ssize_t zero_pages_sharing_show(struct kobject *kobj,
> + struct kobj_attribute *attr, char *buf)
> +{
> + return sysfs_emit(buf, "%ld\n", ksm_zero_pages_sharing);
> +}
> +KSM_ATTR_RO(zero_pages_sharing);
> +
> static ssize_t stable_node_dups_show(struct kobject *kobj,
> struct kobj_attribute *attr, char *buf)
> {
> @@ -3285,6 +3299,7 @@ static struct attribute *ksm_attrs[] = {
> &pages_sharing_attr.attr,
> &pages_unshared_attr.attr,
> &pages_volatile_attr.attr,
> + &zero_pages_sharing_attr.attr,
> &full_scans_attr.attr,
> #ifdef CONFIG_NUMA
> &merge_across_nodes_attr.attr,
