mm: Add NR_WRITEBACK_TEMP counter

Fuse will use temporary buffers to write back dirty data from memory mappings
(normal writes are done synchronously).  This is needed, because there cannot
be any guarantee about the time in which a write will complete.

By using temporary buffers, from the MM's point if view the page is written
back immediately.  If the writeout was due to memory pressure, this
effectively migrates data from a full zone to a less full zone.

This patch adds a new counter (NR_WRITEBACK_TEMP) for the number of pages used
as temporary buffers.

[Lee.Schermerhorn@hp.com: add vmstat_text for NR_WRITEBACK_TEMP]
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Cc: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Lee Schermerhorn <lee.schermerhorn@hp.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

5 files changed, 8 insertions, 1 deletions

diff --git a/drivers/base/node.c b/drivers/base/node.c
index 12fde2d03d69..39f3d1b3a213 100644
--- a/drivers/base/node.c
+++ b/drivers/base/node.c
@@ -77,6 +77,7 @@ static ssize_t node_read_meminfo(struct sys_device * dev, char * buf)
                        "Node %d PageTables:   %8lu kB\n"
                        "Node %d NFS_Unstable: %8lu kB\n"
                        "Node %d Bounce:       %8lu kB\n"
+                       "Node %d WritebackTmp: %8lu kB\n"
                        "Node %d Slab:         %8lu kB\n"
                        "Node %d SReclaimable: %8lu kB\n"
                        "Node %d SUnreclaim:   %8lu kB\n",
@@ -99,6 +100,7 @@ static ssize_t node_read_meminfo(struct sys_device * dev, char * buf)
                        nid, K(node_page_state(nid, NR_PAGETABLE)),
                        nid, K(node_page_state(nid, NR_UNSTABLE_NFS)),
                        nid, K(node_page_state(nid, NR_BOUNCE)),
+                       nid, K(node_page_state(nid, NR_WRITEBACK_TEMP)),
                        nid, K(node_page_state(nid, NR_SLAB_RECLAIMABLE) +
                                 node_page_state(nid, NR_SLAB_UNRECLAIMABLE)),
                        nid, K(node_page_state(nid, NR_SLAB_RECLAIMABLE)),
diff --git a/fs/proc/proc_misc.c b/fs/proc/proc_misc.c
index 48bcf20cec2f..74a323d2b850 100644
--- a/fs/proc/proc_misc.c
+++ b/fs/proc/proc_misc.c
@@ -179,6 +179,7 @@ static int meminfo_read_proc(char *page, char **start, off_t off,
                 "PageTables:   %8lu kB\n"
                 "NFS_Unstable: %8lu kB\n"
                 "Bounce:       %8lu kB\n"
+                "WritebackTmp: %8lu kB\n"
                 "CommitLimit:  %8lu kB\n"
                 "Committed_AS: %8lu kB\n"
                 "VmallocTotal: %8lu kB\n"
@@ -210,6 +211,7 @@ static int meminfo_read_proc(char *page, char **start, off_t off,
                 K(global_page_state(NR_PAGETABLE)),
                 K(global_page_state(NR_UNSTABLE_NFS)),
                 K(global_page_state(NR_BOUNCE)),
+                K(global_page_state(NR_WRITEBACK_TEMP)),
                 K(allowed),
                 K(committed),
                 (unsigned long)VMALLOC_TOTAL >> 10,
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index aad98003176f..ceb675d83a56 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -97,6 +97,7 @@ enum zone_stat_item {
         NR_UNSTABLE_NFS,        /* NFS unstable pages */
         NR_BOUNCE,
         NR_VMSCAN_WRITE,
+        NR_WRITEBACK_TEMP,      /* Writeback using temporary buffers */
 #ifdef CONFIG_NUMA
         NUMA_HIT,               /* allocated in intended node */
         NUMA_MISS,              /* allocated in non intended node */
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index c90a1e8e479f..789b6adbef37 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -211,7 +211,8 @@ clip_bdi_dirty_limit(struct backing_dev_info *bdi, long dirty, long *pbdi_dirty)
         avail_dirty = dirty -
                 (global_page_state(NR_FILE_DIRTY) +
                  global_page_state(NR_WRITEBACK) +
-                 global_page_state(NR_UNSTABLE_NFS));
+                 global_page_state(NR_UNSTABLE_NFS) +
+                 global_page_state(NR_WRITEBACK_TEMP));
 
         if (avail_dirty < 0)
                 avail_dirty = 0;
diff --git a/mm/vmstat.c b/mm/vmstat.c
index 280a7ed549f2..1a32130b958c 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -612,6 +612,7 @@ static const char * const vmstat_text[] = {
         "nr_unstable",
         "nr_bounce",
         "nr_vmscan_write",
+        "nr_writeback_temp",
 
 #ifdef CONFIG_NUMA
         "numa_hit",