| Message ID | 20220824040153.215059-1-xu.xin16@zte.com.cn (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | ksm: count allocated rmap_items and update documentation | expand |
On Wed, Aug 24, 2022 at 04:01:53AM +0000, xu xin wrote: > KSM can save memory by merging identical pages, but also can consume > additional memory, because it needs to generate rmap_items to save > each scanned page's brief rmap information. Some of these pages may > be merged, but some may not be abled to be merged after being checked > several times, which are unprofitable memory consumed. > > The information about whether KSM save memory or consume memory in > system-wide range can be determined by the comprehensive calculation > of pages_sharing, pages_shared, pages_unshared and pages_volatile. > A simple approximate calculation: > > profit =~ pages_sharing * sizeof(page) - (all_rmap_items) * > sizeof(rmap_item); > > where all_rmap_items equals to the sum of pages_sharing, pages_shared, > pages_unshared and pages_volatile. > > But we cannot calculate this kind of ksm profit inner single-process wide > because the information of ksm rmap_item's number of a process is lacked. > For user applications, if this kind of information could be obtained, > it helps upper users know how beneficial the ksm-policy (like madvise) > they are using brings, and then optimize their app code. For example, > one application madvise 1000 pages as MERGEABLE, while only a few pages > are really merged, then it's not cost-efficient. > > So we add a new interface /proc/<pid>/ksm_rmp_items for each process to > indicate the total allocated ksm rmap_items of this process. Similarly, > we can calculate the ksm profit approximately for a single-process by: > > profit =~ ksm_merging_pages * sizeof(page) - ksm_rmp_items * > sizeof(rmap_item); > > where ksm_merging_pages and ksm_rmp_items are both under /proc/<pid>/. > Hmm... I can't apply this patch on linux-next. On what commit this patch series is based on? When submitting patches, don't forget to include --base to git format-patch. Thanks.
diff --git a/fs/proc/base.c b/fs/proc/base.c index 93f7e3d971e4..b6317981492a 100644 --- a/fs/proc/base.c +++ b/fs/proc/base.c @@ -3196,6 +3196,19 @@ static int proc_pid_ksm_merging_pages(struct seq_file *m, struct pid_namespace * return 0; } +static int proc_pid_ksm_rmp_items(struct seq_file *m, struct pid_namespace *ns, + struct pid *pid, struct task_struct *task) +{ + struct mm_struct *mm; + + mm = get_task_mm(task); + if (mm) { + seq_printf(m, "%lu\n", mm->ksm_rmp_items); + mmput(mm); + } + + return 0; +} #endif /* CONFIG_KSM */ #ifdef CONFIG_STACKLEAK_METRICS @@ -3331,6 +3344,7 @@ static const struct pid_entry tgid_base_stuff[] = { #endif #ifdef CONFIG_KSM ONE("ksm_merging_pages", S_IRUSR, proc_pid_ksm_merging_pages), + ONE("ksm_rmp_items", S_IRUSR, proc_pid_ksm_rmp_items), #endif }; @@ -3668,6 +3682,7 @@ static const struct pid_entry tid_base_stuff[] = { #endif #ifdef CONFIG_KSM ONE("ksm_merging_pages", S_IRUSR, proc_pid_ksm_merging_pages), + ONE("ksm_rmp_items", S_IRUSR, proc_pid_ksm_rmp_items), #endif }; diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h index cf97f3884fda..0b9e76275ea7 100644 --- a/include/linux/mm_types.h +++ b/include/linux/mm_types.h @@ -671,6 +671,11 @@ struct mm_struct { * merging. */ unsigned long ksm_merging_pages; + /* + * Represent how many pages are checked for ksm merging + * including merged and not merged. + */ + unsigned long ksm_rmp_items; #endif } __randomize_layout; diff --git a/mm/ksm.c b/mm/ksm.c index 478bcf26bfcd..fc9879d7049f 100644 --- a/mm/ksm.c +++ b/mm/ksm.c @@ -421,6 +421,7 @@ static inline struct rmap_item *alloc_rmap_item(void) static inline void free_rmap_item(struct rmap_item *rmap_item) { ksm_rmap_items--; + rmap_item->mm->ksm_rmp_items--; rmap_item->mm = NULL; /* debug safety */ kmem_cache_free(rmap_item_cache, rmap_item); } @@ -2265,6 +2266,7 @@ static struct rmap_item *get_next_rmap_item(struct mm_slot *mm_slot, if (rmap_item) { /* It has already been zeroed */ rmap_item->mm = mm_slot->mm; + rmap_item->mm->ksm_rmp_items++; rmap_item->address = addr; rmap_item->rmap_list = *rmap_list; *rmap_list = rmap_item;