linux-kernel - [PATCH v2 1/3] pagemap: add mmap-exclusive bit for marking pages mapped only here

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Date:	Tue, 12 May 2015 12:43:03 +0300
From:	Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
To:	linux-mm@...ck.org, Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Mark Williamson <mwilliamson@...o-software.com>,
	Pavel Emelyanov <xemul@...allels.com>,
	linux-api@...r.kernel.org, Andy Lutomirski <luto@...capital.net>,
	Vlastimil Babka <vbabka@...e.cz>, Pavel Machek <pavel@....cz>,
	Mark Seaborn <mseaborn@...omium.org>,
	"Kirill A. Shutemov" <kirill@...temov.name>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Daniel James <djames@...o-software.com>,
	Finn Grimwood <fgrimwood@...o-software.com>
Subject: [PATCH v2 1/3] pagemap: add mmap-exclusive bit for marking pages
 mapped only here

This patch sets bit 56 in pagemap if this page is mapped only once.
It allows to detect exclusively used pages without exposing PFN:

present file exclusive state
0       0    0         non-present
1       1    0         file page mapped somewhere else
1       1    1         file page mapped only here
1       0    0         anon non-CoWed page (shared with parent/child)
1       0    1         anon CoWed page (or never forked)

Signed-off-by: Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
Link: lkml.kernel.org/r/CAEVpBa+_RyACkhODZrRvQLs80iy0sqpdrd0AaP_-tgnX3Y9yNQ@...l.gmail.com

---

v2:
* handle transparent huge pages
* invert bit and rename shared -> exclusive (less confusing name)
---
 Documentation/vm/pagemap.txt |    3 ++-
 fs/proc/task_mmu.c           |   10 ++++++++++
 tools/vm/page-types.c        |   12 ++++++++++++
 3 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/Documentation/vm/pagemap.txt b/Documentation/vm/pagemap.txt
index 6bfbc172cdb9..3cfbbb333ea1 100644
--- a/Documentation/vm/pagemap.txt
+++ b/Documentation/vm/pagemap.txt
@@ -16,7 +16,8 @@ There are three components to pagemap:
     * Bits 0-4   swap type if swapped
     * Bits 5-54  swap offset if swapped
     * Bit  55    pte is soft-dirty (see Documentation/vm/soft-dirty.txt)
-    * Bits 56-60 zero
+    * Bit  56    page exlusively mapped
+    * Bits 57-60 zero
     * Bit  61    page is file-page or shared-anon
     * Bit  62    page swapped
     * Bit  63    page present
diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 6dee68d013ff..29febec65de4 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -982,6 +982,7 @@ struct pagemapread {
 #define PM_STATUS2(v2, x)   (__PM_PSHIFT(v2 ? x : PAGE_SHIFT))
 
 #define __PM_SOFT_DIRTY      (1LL)
+#define __PM_MMAP_EXCLUSIVE  (2LL)
 #define PM_PRESENT          PM_STATUS(4LL)
 #define PM_SWAP             PM_STATUS(2LL)
 #define PM_FILE             PM_STATUS(1LL)
@@ -1074,6 +1075,8 @@ static void pte_to_pagemap_entry(pagemap_entry_t *pme, struct pagemapread *pm,
 
 	if (page && !PageAnon(page))
 		flags |= PM_FILE;
+	if (page && page_mapcount(page) == 1)
+		flags2 |= __PM_MMAP_EXCLUSIVE;
 	if ((vma->vm_flags & VM_SOFTDIRTY))
 		flags2 |= __PM_SOFT_DIRTY;
 
@@ -1119,6 +1122,13 @@ static int pagemap_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
 		else
 			pmd_flags2 = 0;
 
+		if (pmd_present(*pmd)) {
+			struct page *page = pmd_page(*pmd);
+
+			if (page_mapcount(page) == 1)
+				pmd_flags2 |= __PM_MMAP_EXCLUSIVE;
+		}
+
 		for (; addr != end; addr += PAGE_SIZE) {
 			unsigned long offset;
 			pagemap_entry_t pme;
diff --git a/tools/vm/page-types.c b/tools/vm/page-types.c
index 8bdf16b8ba60..3a9f193526ee 100644
--- a/tools/vm/page-types.c
+++ b/tools/vm/page-types.c
@@ -70,9 +70,12 @@
 #define PM_PFRAME(x)        ((x) & PM_PFRAME_MASK)
 
 #define __PM_SOFT_DIRTY      (1LL)
+#define __PM_MMAP_EXCLUSIVE  (2LL)
 #define PM_PRESENT          PM_STATUS(4LL)
 #define PM_SWAP             PM_STATUS(2LL)
+#define PM_FILE             PM_STATUS(1LL)
 #define PM_SOFT_DIRTY       __PM_PSHIFT(__PM_SOFT_DIRTY)
+#define PM_MMAP_EXCLUSIVE   __PM_PSHIFT(__PM_MMAP_EXCLUSIVE)
 
 
 /*
@@ -100,6 +103,8 @@
 #define KPF_SLOB_FREE		49
 #define KPF_SLUB_FROZEN		50
 #define KPF_SLUB_DEBUG		51
+#define KPF_FILE		62
+#define KPF_MMAP_EXCLUSIVE	63
 
 #define KPF_ALL_BITS		((uint64_t)~0ULL)
 #define KPF_HACKERS_BITS	(0xffffULL << 32)
@@ -149,6 +154,9 @@ static const char * const page_flag_names[] = {
 	[KPF_SLOB_FREE]		= "P:slob_free",
 	[KPF_SLUB_FROZEN]	= "A:slub_frozen",
 	[KPF_SLUB_DEBUG]	= "E:slub_debug",
+
+	[KPF_FILE]		= "F:file",
+	[KPF_MMAP_EXCLUSIVE]	= "1:mmap_exclusive",
 };
 
 
@@ -452,6 +460,10 @@ static uint64_t expand_overloaded_flags(uint64_t flags, uint64_t pme)
 
 	if (pme & PM_SOFT_DIRTY)
 		flags |= BIT(SOFTDIRTY);
+	if (pme & PM_FILE)
+		flags |= BIT(FILE);
+	if (pme & PM_MMAP_EXCLUSIVE)
+		flags |= BIT(MMAP_EXCLUSIVE);
 
 	return flags;
 }

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