mm: prepare for removal of obsolete /proc/sys/vm/nr_pdflush_threads

Since per-BDI flusher threads were introduced in 2.6, the pdflush
mechanism is not used any more.  But the old interface exported through
/proc/sys/vm/nr_pdflush_threads still exists and is obviously useless.

For back-compatibility, printk warning information and return 2 to notify
the users that the interface is removed.

Signed-off-by: Wanpeng Li <liwp@linux.vnet.ibm.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>

2 files changed, 4 insertions, 6 deletions

diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 97186b99b0e4..6502d35a25ba 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -1101,11 +1101,9 @@ static struct ctl_table vm_table[] = {
                 .extra1         = &zero,
         },
         {
-                .procname       = "nr_pdflush_threads",
-                .data           = &nr_pdflush_threads,
-                .maxlen         = sizeof nr_pdflush_threads,
-                .mode           = 0444 /* read-only*/,
-                .proc_handler   = proc_dointvec,
+                .procname       = "nr_pdflush_threads",
+                .mode           = 0444 /* read-only */,
+                .proc_handler   = pdflush_proc_obsolete,
         },
         {
                 .procname       = "swappiness",
diff --git a/kernel/sysctl_binary.c b/kernel/sysctl_binary.c
index a650694883a1..65bdcf198d4e 100644
--- a/kernel/sysctl_binary.c
+++ b/kernel/sysctl_binary.c
@@ -147,7 +147,7 @@ static const struct bin_table bin_vm_table[] = {
         { CTL_INT,      VM_DIRTY_RATIO,                 "dirty_ratio" },
         /* VM_DIRTY_WB_CS "dirty_writeback_centisecs" no longer used */
         /* VM_DIRTY_EXPIRE_CS "dirty_expire_centisecs" no longer used */
-        { CTL_INT,      VM_NR_PDFLUSH_THREADS,          "nr_pdflush_threads" },
+        /* VM_NR_PDFLUSH_THREADS "nr_pdflush_threads" no longer used */
         { CTL_INT,      VM_OVERCOMMIT_RATIO,            "overcommit_ratio" },
         /* VM_PAGEBUF unused */
         /* VM_HUGETLB_PAGES "nr_hugepages" no longer used */