[PATCH -mm 14/24] Ramfs and Ram Disk pages are unevictable

[Rik van Riel <riel@redhat.com>]

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From: Lee Schermerhorn <Lee.Schermerhorn@hp.com>

Christoph Lameter pointed out that ram disk pages also clutter the
LRU lists.  When vmscan finds them dirty and tries to clean them,
the ram disk writeback function just redirties the page so that it
goes back onto the active list.  Round and round she goes...

Define new address_space flag [shares address_space flags member
with mapping's gfp mask] to indicate that the address space contains
all unevictable pages.  This will provide for efficient testing
of ramdisk pages in page_evictable().

Also provide wrapper functions to set/test the unevictable state to
minimize #ifdefs in ramdisk driver and any other users of this
facility.

Set the unevictable state on address_space structures for new
ramdisk inodes.  Test the unevictable state in page_evictable()
to cull unevictable pages.

Similarly, ramfs pages are unevictable.  Set the 'unevictable'
address_space flag for new ramfs inodes.

These changes depend on [CONFIG_]UNEVICTABLE_LRU.

Signed-off-by:  Lee Schermerhorn <lee.schermerhorn@hp.com>
Signed-off-by:  Rik van Riel <riel@redhat.com>

 drivers/block/brd.c     |   13 +++++++++++++
 fs/ramfs/inode.c        |    1 +
 include/linux/pagemap.h |   22 ++++++++++++++++++++++
 mm/vmscan.c             |    5 +++++
 4 files changed, 41 insertions(+)

Index: linux-2.6.26-rc5-mm2/include/linux/pagemap.h
===================================================================
--- linux-2.6.26-rc5-mm2.orig/include/linux/pagemap.h	2008-06-10 10:46:23.000000000 -0400
+++ linux-2.6.26-rc5-mm2/include/linux/pagemap.h	2008-06-10 16:47:23.000000000 -0400
@@ -30,6 +30,28 @@ static inline void mapping_set_error(str
 	}
 }
 
+#ifdef CONFIG_UNEVICTABLE_LRU
+#define AS_UNEVICTABLE	(__GFP_BITS_SHIFT + 2)	/* e.g., ramdisk, SHM_LOCK */
+
+static inline void mapping_set_unevictable(struct address_space *mapping)
+{
+	set_bit(AS_UNEVICTABLE, &mapping->flags);
+}
+
+static inline int mapping_unevictable(struct address_space *mapping)
+{
+	if (mapping && (mapping->flags & AS_UNEVICTABLE))
+		return 1;
+	return 0;
+}
+#else
+static inline void mapping_set_unevictable(struct address_space *mapping) { }
+static inline int mapping_unevictable(struct address_space *mapping)
+{
+	return 0;
+}
+#endif
+
 static inline gfp_t mapping_gfp_mask(struct address_space * mapping)
 {
 	return (__force gfp_t)mapping->flags & __GFP_BITS_MASK;
Index: linux-2.6.26-rc5-mm2/mm/vmscan.c
===================================================================
--- linux-2.6.26-rc5-mm2.orig/mm/vmscan.c	2008-06-10 16:25:49.000000000 -0400
+++ linux-2.6.26-rc5-mm2/mm/vmscan.c	2008-06-10 16:47:23.000000000 -0400
@@ -2320,6 +2320,8 @@ int zone_reclaim(struct zone *zone, gfp_
  * lists vs unevictable list.
  *
  * Reasons page might not be evictable:
+ * (1) page's mapping marked unevictable
+ *
  * TODO - later patches
  */
 int page_evictable(struct page *page, struct vm_area_struct *vma)
@@ -2327,6 +2329,9 @@ int page_evictable(struct page *page, st
 
 	VM_BUG_ON(PageUnevictable(page));
 
+	if (mapping_unevictable(page_mapping(page)))
+		return 0;
+
 	/* TODO:  test page [!]evictable conditions */
 
 	return 1;
Index: linux-2.6.26-rc5-mm2/fs/ramfs/inode.c
===================================================================
--- linux-2.6.26-rc5-mm2.orig/fs/ramfs/inode.c	2008-06-10 10:25:06.000000000 -0400
+++ linux-2.6.26-rc5-mm2/fs/ramfs/inode.c	2008-06-10 16:47:23.000000000 -0400
@@ -61,6 +61,7 @@ struct inode *ramfs_get_inode(struct sup
 		inode->i_mapping->a_ops = &ramfs_aops;
 		inode->i_mapping->backing_dev_info = &ramfs_backing_dev_info;
 		mapping_set_gfp_mask(inode->i_mapping, GFP_HIGHUSER);
+		mapping_set_unevictable(inode->i_mapping);
 		inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
 		switch (mode & S_IFMT) {
 		default:
Index: linux-2.6.26-rc5-mm2/drivers/block/brd.c
===================================================================
--- linux-2.6.26-rc5-mm2.orig/drivers/block/brd.c	2008-06-10 10:46:18.000000000 -0400
+++ linux-2.6.26-rc5-mm2/drivers/block/brd.c	2008-06-10 16:47:23.000000000 -0400
@@ -374,8 +374,21 @@ static int brd_ioctl(struct inode *inode
 	return error;
 }
 
+/*
+ * brd_open():
+ * Just mark the mapping as containing unevictable pages
+ */
+static int brd_open(struct inode *inode, struct file *filp)
+{
+	struct address_space *mapping = inode->i_mapping;
+
+	mapping_set_unevictable(mapping);
+	return 0;
+}
+
 static struct block_device_operations brd_fops = {
 	.owner =		THIS_MODULE,
+	.open  =		brd_open,
 	.ioctl =		brd_ioctl,
 #ifdef CONFIG_BLK_DEV_XIP
 	.direct_access =	brd_direct_access,

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