mm: add new KSM process and sysfs knobs

This adds the general_profit KSM sysfs knob and the process profit metric
and process merge type knobs to ksm_stat.

1) split off pages_volatile function

   This splits off the pages_volatile function.  The next patch will
   use this function.

2) expose general_profit metric

   The documentation mentions a general profit metric, however this
   metric is not calculated.  In addition the formula depends on the size
   of internal structures, which makes it more difficult for an
   administrator to make the calculation.  Adding the metric for a better
   user experience.

3) document general_profit sysfs knob

4) calculate ksm process profit metric

   The ksm documentation mentions the process profit metric and how to
   calculate it.  This adds the calculation of the metric.

5) add ksm_merge_type() function

   This adds the ksm_merge_type function.  The function returns the
   merge type for the process.  For madvise it returns "madvise", for
   prctl it returns "process" and otherwise it returns "none".

6) mm: expose ksm process profit metric and merge type in ksm_stat

   This exposes the ksm process profit metric in /proc/<pid>/ksm_stat.
   The name of the value is ksm_merge_type.  The documentation mentions
   the formula for the ksm process profit metric, however it does not
   calculate it.  In addition the formula depends on the size of internal
   structures.  So it makes sense to expose it.

7) document new procfs ksm knobs

Link: https://lkml.kernel.org/r/20230224044000.3084046-3-shr@devkernel.io
Link: https://lkml.kernel.org/r/20230310182851.2579138-3-shr@devkernel.io
Signed-off-by: Stefan Roesch <shr@devkernel.io>
Reviewed-by: Bagas Sanjaya <bagasdotme@gmail.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Rik van Riel <riel@surriel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/Documentation/ABI/testing/sysfs-kernel-mm-ksm b/Documentation/ABI/testing/sysfs-kernel-mm-ksm
index d244674a94806460c61e0afe4f12846a28ab52e3..7768e90f7a8fef7938743ecfc1cc80af4ead2edb 100644 (file)
--- a/Documentation/ABI/testing/sysfs-kernel-mm-ksm
+++ b/Documentation/ABI/testing/sysfs-kernel-mm-ksm
@@ -51,3 +51,11 @@ Description: Control merging pages across different NUMA nodes.
 
                When it is set to 0 only pages from the same node are merged,
                otherwise pages from all nodes can be merged together (default).
+
+What:          /sys/kernel/mm/ksm/general_profit
+Date:          January 2023
+KernelVersion:  6.1
+Contact:       Linux memory management mailing list <linux-mm@kvack.org>
+Description:   Measure how effective KSM is.
+               general_profit: how effective is KSM. The formula for the
+               calculation is in Documentation/admin-guide/mm/ksm.rst.

diff --git a/Documentation/admin-guide/mm/ksm.rst b/Documentation/admin-guide/mm/ksm.rst
index eed51a910c940e19b295eeb3825422a29f6aa39d..6eece5671ab643014e1d999588d18e6490a5be19 100644 (file)
--- a/Documentation/admin-guide/mm/ksm.rst
+++ b/Documentation/admin-guide/mm/ksm.rst
@@ -157,6 +157,8 @@ stable_node_chains_prune_millisecs
 
 The effectiveness of KSM and MADV_MERGEABLE is shown in ``/sys/kernel/mm/ksm/``:
 
+general_profit
+        how effective is KSM. The calculation is explained below.
 pages_shared
         how many shared pages are being used
 pages_sharing
@@ -207,7 +209,8 @@ several times, which are unprofitable memory consumed.
                          ksm_rmap_items * sizeof(rmap_item).
 
    where ksm_merging_pages is shown under the directory ``/proc/<pid>/``,
-   and ksm_rmap_items is shown in ``/proc/<pid>/ksm_stat``.
+   and ksm_rmap_items is shown in ``/proc/<pid>/ksm_stat``. The process profit
+   is also shown in ``/proc/<pid>/ksm_stat`` as ksm_process_profit.
 
 From the perspective of application, a high ratio of ``ksm_rmap_items`` to
 ``ksm_merging_pages`` means a bad madvise-applied policy, so developers or
@@ -218,6 +221,9 @@ so if the ``ksm_rmap_items/ksm_merging_pages`` ratio exceeds 64 on 64-bit CPU
 or exceeds 128 on 32-bit CPU, then the app's madvise policy should be dropped,
 because the ksm profit is approximately zero or negative.
 
+The ksm_merge_type in ``/proc/<pid>/ksm_stat`` shows the merge type of the
+process. Valid values are ``none``, ``madvise`` and ``process``.
+
 Monitoring KSM events
 =====================
 

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 5e0e0ccd47aa760190f75d14d8128264ba0a1b26..c93486fe0dbf0d63a0d8d52286ab5f0b3909d1a1 100644 (file)
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -96,6 +96,7 @@
 #include <linux/time_namespace.h>
 #include <linux/resctrl.h>
 #include <linux/cn_proc.h>
+#include <linux/ksm.h>
 #include <trace/events/oom.h>
 #include "internal.h"
 #include "fd.h"
@@ -3199,6 +3200,7 @@ static int proc_pid_ksm_merging_pages(struct seq_file *m, struct pid_namespace *
 
        return 0;
 }
+
 static int proc_pid_ksm_stat(struct seq_file *m, struct pid_namespace *ns,
                                struct pid *pid, struct task_struct *task)
 {
@@ -3207,6 +3209,9 @@ static int proc_pid_ksm_stat(struct seq_file *m, struct pid_namespace *ns,
        mm = get_task_mm(task);
        if (mm) {
                seq_printf(m, "ksm_rmap_items %lu\n", mm->ksm_rmap_items);
+               seq_printf(m, "ksm_merging_pages %lu\n", mm->ksm_merging_pages);
+               seq_printf(m, "ksm_merge_type %s\n", ksm_merge_type(mm));
+               seq_printf(m, "ksm_process_profit %ld\n", ksm_process_profit(mm));
                mmput(mm);
        }
 

diff --git a/include/linux/ksm.h b/include/linux/ksm.h
index d38a05a36298a7ae7871a918b8189893777056bf..d5f69f18ee5a6d130bf4a0297f67b44c38b379ca 100644 (file)
--- a/include/linux/ksm.h
+++ b/include/linux/ksm.h
@@ -55,6 +55,11 @@ struct page *ksm_might_need_to_copy(struct page *page,
 void rmap_walk_ksm(struct folio *folio, struct rmap_walk_control *rwc);
 void folio_migrate_ksm(struct folio *newfolio, struct folio *folio);
 
+#ifdef CONFIG_PROC_FS
+long ksm_process_profit(struct mm_struct *);
+const char *ksm_merge_type(struct mm_struct *mm);
+#endif /* CONFIG_PROC_FS */
+
 #else  /* !CONFIG_KSM */
 
 static inline int ksm_fork(struct mm_struct *mm, struct mm_struct *oldmm)

diff --git a/mm/ksm.c b/mm/ksm.c
index 4def6f993d986d0b8e586c1f055662d778c12aad..7cd7e12cd3df5f988db7812b9de5c22ab2d2883c 100644 (file)
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -2926,6 +2926,25 @@ static void wait_while_offlining(void)
 }
 #endif /* CONFIG_MEMORY_HOTREMOVE */
 
+#ifdef CONFIG_PROC_FS
+long ksm_process_profit(struct mm_struct *mm)
+{
+       return (long)mm->ksm_merging_pages * PAGE_SIZE -
+               mm->ksm_rmap_items * sizeof(struct ksm_rmap_item);
+}
+
+/* Return merge type name as string. */
+const char *ksm_merge_type(struct mm_struct *mm)
+{
+       if (test_bit(MMF_VM_MERGE_ANY, &mm->flags))
+               return "process";
+       else if (test_bit(MMF_VM_MERGEABLE, &mm->flags))
+               return "madvise";
+       else
+               return "none";
+}
+#endif /* CONFIG_PROC_FS */
+
 #ifdef CONFIG_SYSFS
 /*
  * This all compiles without CONFIG_SYSFS, but is a waste of space.
@@ -3173,8 +3192,7 @@ static ssize_t pages_unshared_show(struct kobject *kobj,
 }
 KSM_ATTR_RO(pages_unshared);
 
-static ssize_t pages_volatile_show(struct kobject *kobj,
-                                  struct kobj_attribute *attr, char *buf)
+static long pages_volatile(void)
 {
        long ksm_pages_volatile;
 
@@ -3186,10 +3204,32 @@ static ssize_t pages_volatile_show(struct kobject *kobj,
         */
        if (ksm_pages_volatile < 0)
                ksm_pages_volatile = 0;
-       return sysfs_emit(buf, "%ld\n", ksm_pages_volatile);
+
+       return ksm_pages_volatile;
+}
+
+static ssize_t pages_volatile_show(struct kobject *kobj,
+                                  struct kobj_attribute *attr, char *buf)
+{
+       return sysfs_emit(buf, "%ld\n", pages_volatile());
 }
 KSM_ATTR_RO(pages_volatile);
 
+static ssize_t general_profit_show(struct kobject *kobj,
+                                  struct kobj_attribute *attr, char *buf)
+{
+       long general_profit;
+       long all_rmap_items;
+
+       all_rmap_items = ksm_max_page_sharing + ksm_pages_shared +
+                               ksm_pages_unshared + pages_volatile();
+       general_profit = ksm_pages_sharing * PAGE_SIZE -
+                               all_rmap_items * sizeof(struct ksm_rmap_item);
+
+       return sysfs_emit(buf, "%ld\n", general_profit);
+}
+KSM_ATTR_RO(general_profit);
+
 static ssize_t stable_node_dups_show(struct kobject *kobj,
                                     struct kobj_attribute *attr, char *buf)
 {
@@ -3254,6 +3294,7 @@ static struct attribute *ksm_attrs[] = {
        &stable_node_dups_attr.attr,
        &stable_node_chains_prune_millisecs_attr.attr,
        &use_zero_pages_attr.attr,
+       &general_profit_attr.attr,
        NULL,
 };