Merge branch 'akpm' (Andrew's patch-bomb)

Merge the rest of Andrew's patches for -rc1:
 "A bunch of fixes and misc missed-out-on things.

  That'll do for -rc1.  I still have a batch of IPC patches which still
  have a possible bug report which I'm chasing down."

* emailed patches from Andrew Morton <akpm@linux-foundation.org>: (25 commits)
  keys: use keyring_alloc() to create module signing keyring
  keys: fix unreachable code
  sendfile: allows bypassing of notifier events
  SGI-XP: handle non-fatal traps
  fat: fix incorrect function comment
  Documentation: ABI: remove testing/sysfs-devices-node
  proc: fix inconsistent lock state
  linux/kernel.h: fix DIV_ROUND_CLOSEST with unsigned divisors
  memcg: don't register hotcpu notifier from ->css_alloc()
  checkpatch: warn on uapi #includes that #include <uapi/...
  revert "rtc: recycle id when unloading a rtc driver"
  mm: clean up transparent hugepage sysfs error messages
  hfsplus: add error message for the case of failure of sync fs in delayed_sync_fs() method
  hfsplus: rework processing of hfs_btree_write() returned error
  hfsplus: rework processing errors in hfsplus_free_extents()
  hfsplus: avoid crash on failed block map free
  kcmp: include linux/ptrace.h
  drivers/rtc/rtc-imxdi.c: must include <linux/spinlock.h>
  mm: cma: WARN if freed memory is still in use
  exec: do not leave bprm->interp on stack
  ...

1 files changed, 20 insertions, 5 deletions

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 6f42712..0713bfb 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -201,6 +201,18 @@ static unsigned long highmem_dirtyable_memory(unsigned long total)
 		     zone_reclaimable_pages(z) - z->dirty_balance_reserve;
 	}
 	/*
+	 * Unreclaimable memory (kernel memory or anonymous memory
+	 * without swap) can bring down the dirtyable pages below
+	 * the zone's dirty balance reserve and the above calculation
+	 * will underflow.  However we still want to add in nodes
+	 * which are below threshold (negative values) to get a more
+	 * accurate calculation but make sure that the total never
+	 * underflows.
+	 */
+	if ((long)x < 0)
+		x = 0;
+
+	/*
 	 * Make sure that the number of highmem pages is never larger
 	 * than the number of the total dirtyable memory. This can only
 	 * occur in very strange VM situations but we want to make sure
@@ -222,8 +234,8 @@ static unsigned long global_dirtyable_memory(void)
 {
 	unsigned long x;
 
-	x = global_page_state(NR_FREE_PAGES) + global_reclaimable_pages() -
-	    dirty_balance_reserve;
+	x = global_page_state(NR_FREE_PAGES) + global_reclaimable_pages();
+	x -= min(x, dirty_balance_reserve);
 
 	if (!vm_highmem_is_dirtyable)
 		x -= highmem_dirtyable_memory(x);
@@ -290,9 +302,12 @@ static unsigned long zone_dirtyable_memory(struct zone *zone)
 	 * highmem zone can hold its share of dirty pages, so we don't
 	 * care about vm_highmem_is_dirtyable here.
 	 */
-	return zone_page_state(zone, NR_FREE_PAGES) +
-	       zone_reclaimable_pages(zone) -
-	       zone->dirty_balance_reserve;
+	unsigned long nr_pages = zone_page_state(zone, NR_FREE_PAGES) +
+		zone_reclaimable_pages(zone);
+
+	/* don't allow this to underflow */
+	nr_pages -= min(nr_pages, zone->dirty_balance_reserve);
+	return nr_pages;
 }
 
 /**