page-writeback.c: subtract min_free_kbytes from dirtyable memory

When calculating amount of dirtyable memory, min_free_kbytes should be
subtracted because it is not intended for dirty pages.

Addresses http://bugs.debian.org/695182

[akpm@linux-foundation.org: fix up min_free_kbytes extern declarations]
[akpm@linux-foundation.org: fix min() warning]
Signed-off-by: Paul Szabo <psz@maths.usyd.edu.au>
Acked-by: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

4 files changed, 6 insertions, 2 deletions

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 1d4122bf6f27..437da0ce78c7 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1393,6 +1393,9 @@ extern void setup_per_cpu_pageset(void);
 extern void zone_pcp_update(struct zone *zone);
 extern void zone_pcp_reset(struct zone *zone);
 
+/* page_alloc.c */
+extern int min_free_kbytes;
+
 /* nommu.c */
 extern atomic_long_t mmap_pages_allocated;
 extern int nommu_shrink_inode_mappings(struct inode *, size_t, size_t);
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 467d8b923fcd..95e9e55602a8 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -105,7 +105,6 @@ extern char core_pattern[];
 extern unsigned int core_pipe_limit;
 #endif
 extern int pid_max;
-extern int min_free_kbytes;
 extern int pid_max_min, pid_max_max;
 extern int sysctl_drop_caches;
 extern int percpu_pagelist_fraction;
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index b1cc6591ed83..c63a21d0e991 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -105,7 +105,6 @@ static int set_recommended_min_free_kbytes(void)
         struct zone *zone;
         int nr_zones = 0;
         unsigned long recommended_min;
-        extern int min_free_kbytes;
 
         if (!khugepaged_enabled())
                 return 0;
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 7300c9d5e1d9..cdc377c456c0 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -241,6 +241,9 @@ static unsigned long global_dirtyable_memory(void)
         if (!vm_highmem_is_dirtyable)
                 x -= highmem_dirtyable_memory(x);
 
+        /* Subtract min_free_kbytes */
+        x -= min_t(unsigned long, x, min_free_kbytes >> (PAGE_SHIFT - 10));
+
         return x + 1;   /* Ensure that we never return 0 */
 }