On 20.06.24 06:39, Sung-hun Kim wrote:
The current version of KSM does not take into account the number of
used ksm_mm_slot. Therefore, when users want to obtain profits of
KSM, KSM omits the memory used for allocating ksm_mm_slots.
This patch introduces a new variable to keep track of the number of
allocated ksm_mm_slots. By doing so, KSM will be able to provide a
more accurate number of the gains made.
If you take a look at the calculation explained in
Documentation/admin-guide/mm/ksm.rst, we only care about rmap_items,
which can grow rather substantially in size.
We also don't consider other metadata, such as the size of the stable
nodes etc. So why should the ksm_mm_slots matter that much that we
should track them and account them?
Any real life examples where this is relevant / a problem.
Signed-off-by: Sung-hun Kim <sfoon.kim@xxxxxxxxxxx>
---
Changelog in V2:
- Add an MMF_VM_MERGEABLE flag check in ksm_process_profit for
untracked processes
---
mm/ksm.c | 13 +++++++++++--
1 file changed, 11 insertions(+), 2 deletions(-)
diff --git a/mm/ksm.c b/mm/ksm.c
index 34c4820e0d3d..c8ced991ccda 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -267,6 +267,9 @@ static unsigned long ksm_pages_unshared;
/* The number of rmap_items in use: to calculate pages_volatile */
static unsigned long ksm_rmap_items;
+/* The number of ksm_mm_slot in use */
+static atomic_long_t ksm_mm_slots = ATOMIC_LONG_INIT(0);
+
/* The number of stable_node chains */
static unsigned long ksm_stable_node_chains;
@@ -1245,6 +1248,7 @@ static int unmerge_and_remove_all_rmap_items(void)
spin_unlock(&ksm_mmlist_lock);
mm_slot_free(mm_slot_cache, mm_slot);
+ atomic_long_dec(&ksm_mm_slots);
clear_bit(MMF_VM_MERGEABLE, &mm->flags);
clear_bit(MMF_VM_MERGE_ANY, &mm->flags);
mmdrop(mm);
@@ -2717,6 +2721,7 @@ static struct ksm_rmap_item *scan_get_next_rmap_item(struct page **page)
spin_unlock(&ksm_mmlist_lock);
mm_slot_free(mm_slot_cache, mm_slot);
+ atomic_long_dec(&ksm_mm_slots);
clear_bit(MMF_VM_MERGEABLE, &mm->flags);
clear_bit(MMF_VM_MERGE_ANY, &mm->flags);
mmap_read_unlock(mm);
@@ -3000,6 +3005,7 @@ int __ksm_enter(struct mm_struct *mm)
list_add_tail(&slot->mm_node, &ksm_scan.mm_slot->slot.mm_node);
spin_unlock(&ksm_mmlist_lock);
+ atomic_long_inc(&ksm_mm_slots);
set_bit(MMF_VM_MERGEABLE, &mm->flags);
mmgrab(mm);
@@ -3042,6 +3048,7 @@ void __ksm_exit(struct mm_struct *mm)
if (easy_to_free) {
mm_slot_free(mm_slot_cache, mm_slot);
+ atomic_long_dec(&ksm_mm_slots);
clear_bit(MMF_VM_MERGE_ANY, &mm->flags);
clear_bit(MMF_VM_MERGEABLE, &mm->flags);
mmdrop(mm);
@@ -3374,7 +3381,8 @@ static void wait_while_offlining(void)
long ksm_process_profit(struct mm_struct *mm)
{
return (long)(mm->ksm_merging_pages + mm_ksm_zero_pages(mm)) * PAGE_SIZE -
- mm->ksm_rmap_items * sizeof(struct ksm_rmap_item);
+ mm->ksm_rmap_items * sizeof(struct ksm_rmap_item) -
+ (test_bit(MMF_VM_MERGEABLE, &mm->flags) ? sizeof(struct ksm_mm_slot) : 0);
}
#endif /* CONFIG_PROC_FS */
@@ -3672,7 +3680,8 @@ static ssize_t general_profit_show(struct kobject *kobj,
long general_profit;
general_profit = (ksm_pages_sharing + atomic_long_read(&ksm_zero_pages)) * PAGE_SIZE -
- ksm_rmap_items * sizeof(struct ksm_rmap_item);
+ ksm_rmap_items * sizeof(struct ksm_rmap_item) -
+ atomic_long_read(&ksm_mm_slots) * sizeof(struct ksm_mm_slot);
return sysfs_emit(buf, "%ld\n", general_profit);
}
--
Cheers,
David / dhildenb
