mm/page-writeback: highmem_is_dirtyable option

Add vm.highmem_is_dirtyable toggle

A 32 bit machine with HIGHMEM64 enabled running DCC has an MMAPed file of
approximately 2Gb size which contains a hash format that is written
randomly by the dbclean process.  On 2.6.16 this process took a few
minutes.  With lowmem only accounting of dirty ratios, this takes about 12
hours of 100% disk IO, all random writes.

Include a toggle in /proc/sys/vm/highmem_is_dirtyable which can be set to 1 to
add the highmem back to the total available memory count.

[akpm@linux-foundation.org: Fix the CONFIG_DETECT_SOFTLOCKUP=y build]
Signed-off-by: Bron Gondwana <brong@fastmail.fm>
Cc: Ethan Solomita <solo@google.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: WU Fengguang <wfg@mail.ustc.edu.cn>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 17 insertions, 1 deletions

diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 7cb1ac3e6fff..d0b47b859067 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -84,8 +84,11 @@ extern int sysctl_stat_interval;
 extern int latencytop_enabled;
 
 /* Constants used for minimum and  maximum */
-#ifdef CONFIG_DETECT_SOFTLOCKUP
+#if defined(CONFIG_DETECT_SOFTLOCKUP) || defined(CONFIG_HIGHMEM)
 static int one = 1;
+#endif
+
+#ifdef CONFIG_DETECT_SOFTLOCKUP
 static int sixty = 60;
 #endif
 
@@ -1150,6 +1153,19 @@ static struct ctl_table vm_table[] = {
                 .extra1         = &zero,
         },
 #endif
+#ifdef CONFIG_HIGHMEM
+        {
+                .ctl_name       = CTL_UNNUMBERED,
+                .procname       = "highmem_is_dirtyable",
+                .data           = &vm_highmem_is_dirtyable,
+                .maxlen         = sizeof(vm_highmem_is_dirtyable),
+                .mode           = 0644,
+                .proc_handler   = &proc_dointvec_minmax,
+                .strategy       = &sysctl_intvec,
+                .extra1         = &zero,
+                .extra2         = &one,
+        },
+#endif
 /*
  * NOTE: do not add new entries to this table unless you have read
  * Documentation/sysctl/ctl_unnumbered.txt