mm: bdi: move statistics to debugfs

Move BDI statistics to debugfs:

   /sys/kernel/debug/bdi/<bdi>/stats

Use postcore_initcall() to initialize the sysfs class and debugfs,
because debugfs is initialized in core_initcall().

Update descriptions in ABI documentation.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

3 files changed, 99 insertions, 48 deletions

diff --git a/Documentation/ABI/testing/sysfs-class-bdi b/Documentation/ABI/testing/sysfs-class-bdi
index c55e811ca180..5ac1e01bbd48 100644
--- a/Documentation/ABI/testing/sysfs-class-bdi
+++ b/Documentation/ABI/testing/sysfs-class-bdi
@@ -3,8 +3,8 @@ Date:		January 2008
 Contact:        Peter Zijlstra <a.p.zijlstra@chello.nl>
 Description:
 
-Provide a place in sysfs for the backing_dev_info object.
-This allows us to see and set the various BDI specific variables.
+Provide a place in sysfs for the backing_dev_info object.  This allows
+setting and retrieving various BDI specific variables.
 
 The <bdi> identifier can be either of the following:
 
@@ -26,34 +26,21 @@ read_ahead_kb (read-write)
 
         Size of the read-ahead window in kilobytes
 
-reclaimable_kb (read-only)
-
-        Reclaimable (dirty or unstable) memory destined for writeback
-        to this device
-
-writeback_kb (read-only)
-
-        Memory currently under writeback to this device
-
-dirty_kb (read-only)
-
-        Global threshold for reclaimable + writeback memory
-
-bdi_dirty_kb (read-only)
-
-        Current threshold on this BDI for reclaimable + writeback
-        memory
-
 min_ratio (read-write)
 
-        Minimal percentage of global dirty threshold allocated to this
-        bdi.  If the value written to this file would make the the sum
-        of all min_ratio values exceed 100, then EINVAL is returned.
-        If min_ratio would become larger than the current max_ratio,
-        then also EINVAL is returned.  The default is zero
+        Under normal circumstances each device is given a part of the
+        total write-back cache that relates to its current average
+        writeout speed in relation to the other devices.
+
+        The 'min_ratio' parameter allows assigning a minimum
+        percentage of the write-back cache to a particular device.
+        For example, this is useful for providing a minimum QoS.
 
 max_ratio (read-write)
 
-        Maximal percentage of global dirty threshold allocated to this
-        bdi.  If max_ratio would become smaller than the current
-        min_ratio, then EINVAL is returned.  The default is 100
+        Allows limiting a particular device to use not more than the
+        given percentage of the write-back cache.  This is useful in
+        situations where we want to avoid one device taking all or
+        most of the write-back cache.  For example in case of an NFS
+        mount that is prone to get stuck, or a FUSE mount which cannot
+        be trusted to play fair.
diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
index ad3271d1e90a..c49a2d045e11 100644
--- a/include/linux/backing-dev.h
+++ b/include/linux/backing-dev.h
@@ -16,6 +16,7 @@
 
 struct page;
 struct device;
+struct dentry;
 
 /*
  * Bits in backing_dev_info.state
@@ -55,6 +56,11 @@ struct backing_dev_info {
         unsigned int max_ratio, max_prop_frac;
 
         struct device *dev;
+
+#ifdef CONFIG_DEBUG_FS
+        struct dentry *debug_dir;
+        struct dentry *debug_stats;
+#endif
 };
 
 int bdi_init(struct backing_dev_info *bdi);
diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index 08361b6aad50..7c4f9e097095 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -10,6 +10,80 @@
 
 static struct class *bdi_class;
 
+#ifdef CONFIG_DEBUG_FS
+#include <linux/debugfs.h>
+#include <linux/seq_file.h>
+
+static struct dentry *bdi_debug_root;
+
+static void bdi_debug_init(void)
+{
+        bdi_debug_root = debugfs_create_dir("bdi", NULL);
+}
+
+static int bdi_debug_stats_show(struct seq_file *m, void *v)
+{
+        struct backing_dev_info *bdi = m->private;
+        long background_thresh;
+        long dirty_thresh;
+        long bdi_thresh;
+
+        get_dirty_limits(&background_thresh, &dirty_thresh, &bdi_thresh, bdi);
+
+#define K(x) ((x) << (PAGE_SHIFT - 10))
+        seq_printf(m,
+                   "BdiWriteback:     %8lu kB\n"
+                   "BdiReclaimable:   %8lu kB\n"
+                   "BdiDirtyThresh:   %8lu kB\n"
+                   "DirtyThresh:      %8lu kB\n"
+                   "BackgroundThresh: %8lu kB\n",
+                   (unsigned long) K(bdi_stat(bdi, BDI_WRITEBACK)),
+                   (unsigned long) K(bdi_stat(bdi, BDI_RECLAIMABLE)),
+                   K(bdi_thresh),
+                   K(dirty_thresh),
+                   K(background_thresh));
+#undef K
+
+        return 0;
+}
+
+static int bdi_debug_stats_open(struct inode *inode, struct file *file)
+{
+        return single_open(file, bdi_debug_stats_show, inode->i_private);
+}
+
+static const struct file_operations bdi_debug_stats_fops = {
+        .open           = bdi_debug_stats_open,
+        .read           = seq_read,
+        .llseek         = seq_lseek,
+        .release        = single_release,
+};
+
+static void bdi_debug_register(struct backing_dev_info *bdi, const char *name)
+{
+        bdi->debug_dir = debugfs_create_dir(name, bdi_debug_root);
+        bdi->debug_stats = debugfs_create_file("stats", 0444, bdi->debug_dir,
+                                               bdi, &bdi_debug_stats_fops);
+}
+
+static void bdi_debug_unregister(struct backing_dev_info *bdi)
+{
+        debugfs_remove(bdi->debug_stats);
+        debugfs_remove(bdi->debug_dir);
+}
+#else
+static inline void bdi_debug_init(void)
+{
+}
+static inline void bdi_debug_register(struct backing_dev_info *bdi,
+                                      const char *name)
+{
+}
+static inline void bdi_debug_unregister(struct backing_dev_info *bdi)
+{
+}
+#endif
+
 static ssize_t read_ahead_kb_store(struct device *dev,
                                   struct device_attribute *attr,
                                   const char *buf, size_t count)
@@ -40,21 +114,6 @@ static ssize_t name##_show(struct device *dev,				\
 
 BDI_SHOW(read_ahead_kb, K(bdi->ra_pages))
 
-BDI_SHOW(reclaimable_kb, K(bdi_stat(bdi, BDI_RECLAIMABLE)))
-BDI_SHOW(writeback_kb, K(bdi_stat(bdi, BDI_WRITEBACK)))
-
-static inline unsigned long get_dirty(struct backing_dev_info *bdi, int i)
-{
-        unsigned long thresh[3];
-
-        get_dirty_limits(&thresh[0], &thresh[1], &thresh[2], bdi);
-
-        return thresh[i];
-}
-
-BDI_SHOW(dirty_kb, K(get_dirty(bdi, 1)))
-BDI_SHOW(bdi_dirty_kb, K(get_dirty(bdi, 2)))
-
 static ssize_t min_ratio_store(struct device *dev,
                 struct device_attribute *attr, const char *buf, size_t count)
 {
@@ -95,10 +154,6 @@ BDI_SHOW(max_ratio, bdi->max_ratio)
 
 static struct device_attribute bdi_dev_attrs[] = {
         __ATTR_RW(read_ahead_kb),
-        __ATTR_RO(reclaimable_kb),
-        __ATTR_RO(writeback_kb),
-        __ATTR_RO(dirty_kb),
-        __ATTR_RO(bdi_dirty_kb),
         __ATTR_RW(min_ratio),
         __ATTR_RW(max_ratio),
         __ATTR_NULL,
@@ -108,10 +163,11 @@ static __init int bdi_class_init(void)
 {
         bdi_class = class_create(THIS_MODULE, "bdi");
         bdi_class->dev_attrs = bdi_dev_attrs;
+        bdi_debug_init();
         return 0;
 }
 
-core_initcall(bdi_class_init);
+postcore_initcall(bdi_class_init);
 
 int bdi_register(struct backing_dev_info *bdi, struct device *parent,
                 const char *fmt, ...)
@@ -136,6 +192,7 @@ int bdi_register(struct backing_dev_info *bdi, struct device *parent,
 
         bdi->dev = dev;
         dev_set_drvdata(bdi->dev, bdi);
+        bdi_debug_register(bdi, name);
 
 exit:
         kfree(name);
@@ -152,6 +209,7 @@ EXPORT_SYMBOL(bdi_register_dev);
 void bdi_unregister(struct backing_dev_info *bdi)
 {
         if (bdi->dev) {
+                bdi_debug_unregister(bdi);
                 device_unregister(bdi->dev);
                 bdi->dev = NULL;
         }