[RFC] pin page control subsystem

[Minchan Kim]

Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
---
 mm/Makefile   |    2 +-
 mm/pin-page.c |  101 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 102 insertions(+), 1 deletion(-)
 create mode 100644 mm/pin-page.c

diff --git a/mm/Makefile b/mm/Makefile
index f008033..245c2f7 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -5,7 +5,7 @@
 mmu-y			:= nommu.o
 mmu-$(CONFIG_MMU)	:= fremap.o highmem.o madvise.o memory.o mincore.o \
 			   mlock.o mmap.o mprotect.o mremap.o msync.o rmap.o \
-			   vmalloc.o pagewalk.o pgtable-generic.o
+			   vmalloc.o pagewalk.o pgtable-generic.o pin-page.o
 
 ifdef CONFIG_CROSS_MEMORY_ATTACH
 mmu-$(CONFIG_MMU)	+= process_vm_access.o
diff --git a/mm/pin-page.c b/mm/pin-page.c
new file mode 100644
index 0000000..74b07f8
--- /dev/null
+++ b/mm/pin-page.c
@@ -0,0 +1,101 @@
+#include <linux/mm.h>
+#include <linux/slab.h>
+#include <linux/list.h>
+#include <linux/hashtable.h>
+
+#define PPAGE_HASH_BITS 10
+
+static DEFINE_SPINLOCK(hash_lock);
+/*
+ * Should consider what's data struct we should use.
+ * It would be better use radix tree if we try to pin contigous
+ * pages a lot but if we pin spread pages, it wouldn't be a good idea.
+ */
+static DEFINE_HASHTABLE(pin_page_hash, PPAGE_HASH_BITS);
+
+/*
+ * Each subsystems should provide own page migration handler
+ */
+struct pin_page_owner {
+	int (*migrate)(struct page *page, void *private);
+};
+
+struct pin_page_info {
+	struct pin_page_owner *owner;
+	struct hlist_node hlist;
+
+	unsigned long pfn;
+	void *private;
+};
+
+/* TODO : Introduce new page flags */
+void SetPinnedPage(struct page *page)
+{
+
+}
+
+int PinnedPage(struct page *page)
+{
+	return 0;
+}
+
+/*
+ * GUP caller or subsystems which pin the page should call this function
+ * to register @page in pin-page control subsystem so that VM can ask us
+ * when it want to migrate @page.
+ *  
+ * Each pinned page would have some private key to identify itself
+ * like custom-allocator-returned handle.
+ */
+int set_pinned_page(struct pin_page_owner *owner,
+			struct page *page, void *private)
+{
+	struct pin_page_info *pinfo = kmalloc(sizeof(pinfo), GFP_KERNEL);
+
+	INIT_HLIST_NODE(&pinfo->hlist);
+	pinfo->owner = owner;
+
+	pinfo->pfn = page_to_pfn(page);
+	pinfo->private = private;
+	
+	spin_lock(&hash_lock);
+	hash_add(pin_page_hash, &pinfo->hlist, pinfo->pfn);
+	spin_unlock(&hash_lock);
+
+	SetPinnedPage(page);
+	return 0;
+};
+
+struct pin_page_info *get_pin_page_info(struct page *page)
+{
+	struct pin_page_info *tmp;
+	unsigned long pfn = page_to_pfn(page);
+
+	spin_lock(&hash_lock);
+	hash_for_each_possible(pin_page_hash, tmp, hlist, pfn) {
+		if (tmp->pfn == pfn) {
+			spin_unlock(&hash_lock);
+			return tmp;
+		}
+	}
+	spin_unlock(&hash_lock);
+	return NULL;
+}
+
+/* Used in compaction.c */
+int migrate_pinned_page(struct page *page)
+{
+	int ret = 1;
+	struct pin_page_info *pinfo = NULL;
+
+	if (PinnedPage(page)) {
+		while ((pinfo = get_pin_page_info(page))) {
+			/* If one of owners failed, bail out */
+			if (pinfo->owner->migrate(page, pinfo->private))
+				break;
+		}
+
+		ret = 0;
+	}
+	return ret;
+}
-- 
1.7.9.5

-- 
Kind regards,
Minchan Kim
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