[RFC PATCH] KSM: Auto add flag new VMA as VM_MERGEABLE

[Timofey Titovets <nefelim4ag@gmail.com>]

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Hi list.

This is a small patch what allow ksm dedupe "whole" system memory.
I think what people with tiny pc and android developers will be happy 
after this patch.
I just like clear memory =].

I have tested it and it working very good. For testing apply it and 
enable ksm:
echo 1 | sudo tee /sys/kernel/mm/ksm/run
This show how much memory saved:
echo $[$(cat /sys/kernel/mm/ksm/pages_shared)*$(getconf PAGE_SIZE)/1024 ]KB

(i use linux-next-git 20141031)

It add very small overhead to mmap call's.

Please check my code, may be i should move new functions to other file?
I think about sysfs switcher like:
/sys/kernel/mm/ksm/mark_new_vma # 0 or 1 if 1 new vma will be marked 
like VM_MERGEABLE.

Can you advise me something?

I implement 2 new functions:
ksm_vm_flags_mod() - working only in mm/mmap.c file, change default flags
ksm_vma_add_new() - add new created vma to ksm internal tree

If you see broken patch lines i have also attach patch.

 From db8ad0877146a69e1e5d5ab98825cefcf44a95bb Mon Sep 17 00:00:00 2001
From: Timofey Titovets <nefelim4ag@gmail.com>
Date: Sat, 8 Nov 2014 03:02:52 +0300
Subject: [PATCH] KSM: Add auto flag new VMA as VM_MERGEABLE

Signed-off-by: Timofey Titovets <nefelim4ag@gmail.com>
---
  include/linux/ksm.h | 31 +++++++++++++++++++++++++++++++
  mm/mmap.c           | 17 +++++++++++++++++
  2 files changed, 48 insertions(+)

diff --git a/include/linux/ksm.h b/include/linux/ksm.h
index 3be6bb1..c3fff64 100644
--- a/include/linux/ksm.h
+++ b/include/linux/ksm.h
@@ -76,6 +76,29 @@ struct page *ksm_might_need_to_copy(struct page *page,
  int rmap_walk_ksm(struct page *page, struct rmap_walk_control *rwc);
  void ksm_migrate_page(struct page *newpage, struct page *oldpage);

+/*
+ * Allow to mark new vma as VM_MERGEABLE
+ */
+#ifndef VM_SAO
+#define VM_SAO 0
+#endif
+static inline void ksm_vm_flags_mod(unsigned long *vm_flags)
+{
+	if (*vm_flags & (VM_MERGEABLE | VM_SHARED  | VM_MAYSHARE   |
+			 VM_PFNMAP    | VM_IO      | VM_DONTEXPAND |
+			 VM_HUGETLB | VM_NONLINEAR | VM_MIXEDMAP   | VM_SAO) )
+		return;
+	*vm_flags |= VM_MERGEABLE;
+}
+
+static inline void ksm_vma_add_new(struct vm_area_struct *vma)
+{
+	struct mm_struct *mm = vma->vm_mm;
+	if (!test_bit(MMF_VM_MERGEABLE, &mm->flags)) {
+		__ksm_enter(mm);
+	}
+}
+
  #else  /* !CONFIG_KSM */

  static inline int ksm_fork(struct mm_struct *mm, struct mm_struct *oldmm)
@@ -92,6 +115,14 @@ static inline int PageKsm(struct page *page)
  	return 0;
  }

+static inline void ksm_vm_flags_mod(unsigned long *vm_flags_p)
+{
+}
+
+void ksm_vma_add_new(struct vm_area_struct *vma)
+{
+}
+
  #ifdef CONFIG_MMU
  static inline int ksm_madvise(struct vm_area_struct *vma, unsigned 
long start,
  		unsigned long end, int advice, unsigned long *vm_flags)
diff --git a/mm/mmap.c b/mm/mmap.c
index 7f85520..ce0073e 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -41,6 +41,7 @@
  #include <linux/notifier.h>
  #include <linux/memory.h>
  #include <linux/printk.h>
+#include <linux/ksm.h>

  #include <asm/uaccess.h>
  #include <asm/cacheflush.h>
@@ -911,10 +912,14 @@ again:			remove_next = 1 + (end > next->vm_end);
  			vma_gap_update(next);
  		else
  			mm->highest_vm_end = end;
+	} else {
+		if (next && !insert)
+			ksm_vma_add_new(next);
  	}
  	if (insert && file)
  		uprobe_mmap(insert);

+	ksm_vma_add_new(vma);
  	validate_mm(mm);

  	return 0;
@@ -1307,6 +1312,9 @@ unsigned long do_mmap_pgoff(struct file *file, 
unsigned long addr,
  	vm_flags = calc_vm_prot_bits(prot) | calc_vm_flag_bits(flags) |
  			mm->def_flags | VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC;

+	/* If ksm is enabled, we add VM_MERGABLE to new VMAs. */
+	ksm_vm_flags_mod(&vm_flags);
+
  	if (flags & MAP_LOCKED)
  		if (!can_do_mlock())
  			return -EPERM;
@@ -1648,6 +1656,7 @@ munmap_back:
  			allow_write_access(file);
  	}
  	file = vma->vm_file;
+	ksm_vma_add_new(vma);
  out:
  	perf_event_mmap(vma);

@@ -2484,6 +2493,8 @@ static int __split_vma(struct mm_struct *mm, 
struct vm_area_struct *vma,
  	else
  		err = vma_adjust(vma, vma->vm_start, addr, vma->vm_pgoff, new);

+	ksm_vma_add_new(vma);
+
  	/* Success. */
  	if (!err)
  		return 0;
@@ -2659,6 +2670,9 @@ static unsigned long do_brk(unsigned long addr, 
unsigned long len)
  	if (error)
  		return error;

+	/* If ksm is enabled, we add VM_MERGABLE to new VMAs. */
+	ksm_vm_flags_mod(&flags);
+
  	/*
  	 * mm->mmap_sem is required to protect against another thread
  	 * changing the mappings in case we sleep.
@@ -2708,6 +2722,7 @@ static unsigned long do_brk(unsigned long addr, 
unsigned long len)
  	vma->vm_flags = flags;
  	vma->vm_page_prot = vm_get_page_prot(flags);
  	vma_link(mm, vma, prev, rb_link, rb_parent);
+	ksm_vma_add_new(vma);
  out:
  	perf_event_mmap(vma);
  	mm->total_vm += len >> PAGE_SHIFT;
@@ -2887,6 +2902,7 @@ struct vm_area_struct *copy_vma(struct 
vm_area_struct **vmap,
  				new_vma->vm_ops->open(new_vma);
  			vma_link(mm, new_vma, prev, rb_link, rb_parent);
  			*need_rmap_locks = false;
+			ksm_vma_add_new(new_vma);
  		}
  	}
  	return new_vma;
@@ -3004,6 +3020,7 @@ static struct vm_area_struct 
*__install_special_mapping(
  	mm->total_vm += len >> PAGE_SHIFT;

  	perf_event_mmap(vma);
+	ksm_vma_add_new(vma);

  	return vma;

-- 
2.1.3


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