[PATCH RFC 4/5] mm/ksm, proc: introduce remote merge

[Oleksandr Natalenko]

Use previously introduced remote madvise knob to mark task's
anonymous memory as mergeable.

To force merging task's VMAs, "merge" hint is used:

   # echo merge > /proc/<pid>/madvise

Force unmerging is done similarly:

   # echo unmerge > /proc/<pid>/madvise

To achieve this, previously introduced ksm_madvise_*() helpers
are used.

Signed-off-by: Oleksandr Natalenko <oleksa...@redhat.com>
---
 fs/proc/base.c | 52 +++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 51 insertions(+), 1 deletion(-)

diff --git a/fs/proc/base.c b/fs/proc/base.c
index f69532d6b74f..6677580080ed 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -94,6 +94,8 @@
 #include <linux/sched/debug.h>
 #include <linux/sched/stat.h>
 #include <linux/posix-timers.h>
+#include <linux/mman.h>
+#include <linux/ksm.h>
 #include <trace/events/oom.h>
 #include "internal.h"
 #include "fd.h"
@@ -2960,15 +2962,63 @@ static int proc_stack_depth(struct seq_file *m, struct 
pid_namespace *ns,
 static ssize_t madvise_write(struct file *file, const char __user *buf,
                size_t count, loff_t *ppos)
 {
+       /* For now, only KSM hints are implemented */
+#ifdef CONFIG_KSM
+       char buffer[PROC_NUMBUF];
+       int behaviour;
        struct task_struct *task;
+       struct mm_struct *mm;
+       int err = 0;
+       struct vm_area_struct *vma;
+
+       memset(buffer, 0, sizeof(buffer));
+       if (count > sizeof(buffer) - 1)
+               count = sizeof(buffer) - 1;
+       if (copy_from_user(buffer, buf, count))
+               return -EFAULT;
+
+       if (!memcmp("merge", buffer, min(sizeof("merge")-1, count)))
+               behaviour = MADV_MERGEABLE;
+       else if (!memcmp("unmerge", buffer, min(sizeof("unmerge")-1, count)))
+               behaviour = MADV_UNMERGEABLE;
+       else
+               return -EINVAL;
 
        task = get_proc_task(file_inode(file));
        if (!task)
                return -ESRCH;
 
+       mm = get_task_mm(task);
+       if (!mm) {
+               err = -EINVAL;
+               goto out_put_task_struct;
+       }
+
+       down_write(&mm->mmap_sem);
+       switch (behaviour) {
+       case MADV_MERGEABLE:
+       case MADV_UNMERGEABLE:
+               vma = mm->mmap;
+               while (vma) {
+                       if (behaviour == MADV_MERGEABLE)
+                               ksm_madvise_merge(vma->vm_mm, vma, 
&vma->vm_flags);
+                       else
+                               ksm_madvise_unmerge(vma, vma->vm_start, 
vma->vm_end, &vma->vm_flags);
+                       vma = vma->vm_next;
+               }
+               break;
+       }
+       up_write(&mm->mmap_sem);
+
+       mmput(mm);
+
+out_put_task_struct:
        put_task_struct(task);
 
-       return count;
+       return err ? err : count;
+#else
+       return -EINVAL;
+#endif /* CONFIG_KSM */
 }
 
 static const struct file_operations proc_madvise_operations = {
-- 
2.21.0