mm: bdi: export BDI attributes in sysfs

Provide a place in sysfs (/sys/class/bdi) for the backing_dev_info object.
This allows us to see and set the various BDI specific variables.

In particular this properly exposes the read-ahead window for all relevant
users and /sys/block/<block>/queue/read_ahead_kb should be deprecated.

With patient help from Kay Sievers and Greg KH

[mszeredi@suse.cz]

 - split off NFS and FUSE changes into separate patches
 - document new sysfs attributes under Documentation/ABI
 - do bdi_class_init as a core_initcall, otherwise the "default" BDI
   won't be initialized
 - remove bdi_init_fmt macro, it's not used very much

[akpm@linux-foundation.org: fix ia64 warning]
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Kay Sievers <kay.sievers@vrfy.org>
Acked-by: Greg KH <greg@kroah.com>
Cc: Trond Myklebust <trond.myklebust@fys.uio.no>
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>

8 files changed, 194 insertions, 2 deletions

diff --git a/Documentation/ABI/testing/sysfs-class-bdi b/Documentation/ABI/testing/sysfs-class-bdi
new file mode 100644
index 000000000000..b800cdda40bb
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-class-bdi
@@ -0,0 +1,46 @@
+What:           /sys/class/bdi/<bdi>/
+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.
+
+The <bdi> identifier can be either of the following:
+
+MAJOR:MINOR
+
+        Device number for block devices, or value of st_dev on
+        non-block filesystems which provide their own BDI, such as NFS
+        and FUSE.
+
+default
+
+        The default backing dev, used for non-block device backed
+        filesystems which do not provide their own BDI.
+
+Files under /sys/class/bdi/<bdi>/
+---------------------------------
+
+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
+
diff --git a/block/genhd.c b/block/genhd.c
index 00da5219ee37..fda9c7a63c29 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -182,11 +182,17 @@ static int exact_lock(dev_t devt, void *data)
  */
 void add_disk(struct gendisk *disk)
 {
+        struct backing_dev_info *bdi;
+
         disk->flags |= GENHD_FL_UP;
         blk_register_region(MKDEV(disk->major, disk->first_minor),
                             disk->minors, NULL, exact_match, exact_lock, disk);
         register_disk(disk);
         blk_register_queue(disk);
+
+        bdi = &disk->queue->backing_dev_info;
+        bdi_register_dev(bdi, MKDEV(disk->major, disk->first_minor));
+        sysfs_create_link(&disk->dev.kobj, &bdi->dev->kobj, "bdi");
 }
 
 EXPORT_SYMBOL(add_disk);
@@ -194,6 +200,8 @@ EXPORT_SYMBOL(del_gendisk);	/* in partitions/check.c */
 
 void unlink_gendisk(struct gendisk *disk)
 {
+        sysfs_remove_link(&disk->dev.kobj, "bdi");
+        bdi_unregister(&disk->queue->backing_dev_info);
         blk_unregister_queue(disk);
         blk_unregister_region(MKDEV(disk->major, disk->first_minor),
                               disk->minors);
diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
index b66fa2bdfd9c..6d513666d45c 100644
--- a/include/linux/backing-dev.h
+++ b/include/linux/backing-dev.h
@@ -11,9 +11,11 @@
 #include <linux/percpu_counter.h>
 #include <linux/log2.h>
 #include <linux/proportions.h>
+#include <linux/kernel.h>
 #include <asm/atomic.h>
 
 struct page;
+struct device;
 
 /*
  * Bits in backing_dev_info.state
@@ -48,11 +50,18 @@ struct backing_dev_info {
 
         struct prop_local_percpu completions;
         int dirty_exceeded;
+
+        struct device *dev;
 };
 
 int bdi_init(struct backing_dev_info *bdi);
 void bdi_destroy(struct backing_dev_info *bdi);
 
+int bdi_register(struct backing_dev_info *bdi, struct device *parent,
+                const char *fmt, ...);
+int bdi_register_dev(struct backing_dev_info *bdi, dev_t dev);
+void bdi_unregister(struct backing_dev_info *bdi);
+
 static inline void __add_bdi_stat(struct backing_dev_info *bdi,
                 enum bdi_stat_item item, s64 amount)
 {
diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index b7b3362f7717..f462439cc288 100644
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -114,6 +114,9 @@ struct file;
 int dirty_writeback_centisecs_handler(struct ctl_table *, int, struct file *,
                                       void __user *, size_t *, loff_t *);
 
+void get_dirty_limits(long *pbackground, long *pdirty, long *pbdi_dirty,
+                 struct backing_dev_info *bdi);
+
 void page_writeback_init(void);
 void balance_dirty_pages_ratelimited_nr(struct address_space *mapping,
                                         unsigned long nr_pages_dirtied);
diff --git a/lib/percpu_counter.c b/lib/percpu_counter.c
index 393a0e915c23..119174494cb5 100644
--- a/lib/percpu_counter.c
+++ b/lib/percpu_counter.c
@@ -102,6 +102,7 @@ void percpu_counter_destroy(struct percpu_counter *fbc)
                 return;
 
         free_percpu(fbc->counters);
+        fbc->counters = NULL;
 #ifdef CONFIG_HOTPLUG_CPU
         mutex_lock(&percpu_counters_lock);
         list_del(&fbc->list);
diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index e8644b1e5527..847eabe4824c 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -4,12 +4,129 @@
 #include <linux/fs.h>
 #include <linux/sched.h>
 #include <linux/module.h>
+#include <linux/writeback.h>
+#include <linux/device.h>
+
+
+static struct class *bdi_class;
+
+static ssize_t read_ahead_kb_store(struct device *dev,
+                                  struct device_attribute *attr,
+                                  const char *buf, size_t count)
+{
+        struct backing_dev_info *bdi = dev_get_drvdata(dev);
+        char *end;
+        unsigned long read_ahead_kb;
+        ssize_t ret = -EINVAL;
+
+        read_ahead_kb = simple_strtoul(buf, &end, 10);
+        if (*buf && (end[0] == '\0' || (end[0] == '\n' && end[1] == '\0'))) {
+                bdi->ra_pages = read_ahead_kb >> (PAGE_SHIFT - 10);
+                ret = count;
+        }
+        return ret;
+}
+
+#define K(pages) ((pages) << (PAGE_SHIFT - 10))
+
+#define BDI_SHOW(name, expr)                                            \
+static ssize_t name##_show(struct device *dev,                          \
+                           struct device_attribute *attr, char *page)   \
+{                                                                       \
+        struct backing_dev_info *bdi = dev_get_drvdata(dev);            \
+                                                                        \
+        return snprintf(page, PAGE_SIZE-1, "%lld\n", (long long)expr);  \
+}
+
+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)))
+
+#define __ATTR_RW(attr) __ATTR(attr, 0644, attr##_show, attr##_store)
+
+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_NULL,
+};
+
+static __init int bdi_class_init(void)
+{
+        bdi_class = class_create(THIS_MODULE, "bdi");
+        bdi_class->dev_attrs = bdi_dev_attrs;
+        return 0;
+}
+
+core_initcall(bdi_class_init);
+
+int bdi_register(struct backing_dev_info *bdi, struct device *parent,
+                const char *fmt, ...)
+{
+        char *name;
+        va_list args;
+        int ret = 0;
+        struct device *dev;
+
+        va_start(args, fmt);
+        name = kvasprintf(GFP_KERNEL, fmt, args);
+        va_end(args);
+
+        if (!name)
+                return -ENOMEM;
+
+        dev = device_create(bdi_class, parent, MKDEV(0, 0), name);
+        if (IS_ERR(dev)) {
+                ret = PTR_ERR(dev);
+                goto exit;
+        }
+
+        bdi->dev = dev;
+        dev_set_drvdata(bdi->dev, bdi);
+
+exit:
+        kfree(name);
+        return ret;
+}
+EXPORT_SYMBOL(bdi_register);
+
+int bdi_register_dev(struct backing_dev_info *bdi, dev_t dev)
+{
+        return bdi_register(bdi, NULL, "%u:%u", MAJOR(dev), MINOR(dev));
+}
+EXPORT_SYMBOL(bdi_register_dev);
+
+void bdi_unregister(struct backing_dev_info *bdi)
+{
+        if (bdi->dev) {
+                device_unregister(bdi->dev);
+                bdi->dev = NULL;
+        }
+}
+EXPORT_SYMBOL(bdi_unregister);
 
 int bdi_init(struct backing_dev_info *bdi)
 {
         int i;
         int err;
 
+        bdi->dev = NULL;
+
         for (i = 0; i < NR_BDI_STAT_ITEMS; i++) {
                 err = percpu_counter_init_irq(&bdi->bdi_stat[i], 0);
                 if (err)
@@ -33,6 +150,8 @@ void bdi_destroy(struct backing_dev_info *bdi)
 {
         int i;
 
+        bdi_unregister(bdi);
+
         for (i = 0; i < NR_BDI_STAT_ITEMS; i++)
                 percpu_counter_destroy(&bdi->bdi_stat[i]);
 
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 5e00f1772c20..e5b6b1190a95 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -300,7 +300,7 @@ static unsigned long determine_dirtyable_memory(void)
         return x + 1;   /* Ensure that we never return 0 */
 }
 
-static void
+void
 get_dirty_limits(long *pbackground, long *pdirty, long *pbdi_dirty,
                  struct backing_dev_info *bdi)
 {
diff --git a/mm/readahead.c b/mm/readahead.c
index 8762e8988972..d8723a5f6496 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -235,7 +235,13 @@ unsigned long max_sane_readahead(unsigned long nr)
 
 static int __init readahead_init(void)
 {
-        return bdi_init(&default_backing_dev_info);
+        int err;
+
+        err = bdi_init(&default_backing_dev_info);
+        if (!err)
+                bdi_register(&default_backing_dev_info, NULL, "default");
+
+        return err;
 }
 subsys_initcall(readahead_init);