[PATCH v5] remove no longer use of pdflush interface

From: Wanpeng Li
Date: Sun Jun 10 2012 - 20:29:21 EST

From: Wanpeng Li <liwp@xxxxxxxxxxxxxxxxxx>

Since per-BDI flusher introduced to linux 2.6, pdflush mechanism is not
used any more, but the old interface of pdflush exported through /proc/sys/vm/
is still existing and obviously useless. In order for back-compatibility,
printk warning information and return 0 to notify the users that the
interface is removed.

Signed-off-by: Wanpeng Li <liwp@xxxxxxxxxxxxxxxxxx>

"V4 -> V5":

* remove useless comment
* copy "0\n" out to userspace and return 2

"V3 -> V4":

* replace generic proc_obsolete() by pdflush_proc_obsolete() which just
addresses old pdflush interface

"V2 -> V3":

* rename proc_deprecated() to proc_obsolete()
* replace printk in proc_obsolete by prink_once and change warning
* information

"V1 -> V2":

* add printk warning
* add description in Documentation
---
.../ABI/obsolete/proc-sys-vm-nr_pdflush_threads | 5 +++++
Documentation/feature-removal-schedule.txt | 8 ++++++++
Documentation/sysctl/vm.txt | 11 -----------
fs/fs-writeback.c | 5 -----
include/linux/backing-dev.h | 3 +++
include/linux/writeback.h | 5 -----
kernel/sysctl.c | 8 +++-----
kernel/sysctl_binary.c | 2 +-
mm/backing-dev.c | 20 ++++++++++++++++++++
9 files changed, 40 insertions(+), 27 deletions(-)
create mode 100644 Documentation/ABI/obsolete/proc-sys-vm-nr_pdflush_threads

diff --git a/Documentation/ABI/obsolete/proc-sys-vm-nr_pdflush_threads b/Documentation/ABI/obsolete/proc-sys-vm-nr_pdflush_threads
new file mode 100644
index 0000000..b0b0eeb
--- /dev/null
+++ b/Documentation/ABI/obsolete/proc-sys-vm-nr_pdflush_threads
@@ -0,0 +1,5 @@
+What: /proc/sys/vm/nr_pdflush_threads
+Date: June 2012
+Contact: Wanpeng Li <liwp@xxxxxxxxxxxxxxxxxx>
+Description: Since pdflush is replaced by per-BDI flusher, the interface of old pdflush
+ exported in /proc/sys/vm/ should be removed.
diff --git a/Documentation/feature-removal-schedule.txt b/Documentation/feature-removal-schedule.txt
index 56000b3..8e4a60c 100644
--- a/Documentation/feature-removal-schedule.txt
+++ b/Documentation/feature-removal-schedule.txt
@@ -13,6 +13,14 @@ Who: Jim Cromie <jim.cromie@xxxxxxxxx>, Jason Baron <jbaron@xxxxxxxxxx>

---------------------------

+What: /proc/sys/vm/nr_pdflush_threads
+When: 2012
+Why: Since pdflush is deprecated, the interface exported in /proc/sys/vm/
+ should be removed.
+Who: Wanpeng Li <liwp@xxxxxxxxxxxxxxxxxx>
+
+---------------------------
+
What: CONFIG_APM_CPU_IDLE, and its ability to call APM BIOS in idle
When: 2012
Why: This optional sub-feature of APM is of dubious reliability,
diff --git a/Documentation/sysctl/vm.txt b/Documentation/sysctl/vm.txt
index 96f0ee8..71c17d2 100644
--- a/Documentation/sysctl/vm.txt
+++ b/Documentation/sysctl/vm.txt
@@ -42,7 +42,6 @@ Currently, these files are in /proc/sys/vm:
- mmap_min_addr
- nr_hugepages
- nr_overcommit_hugepages
-- nr_pdflush_threads
- nr_trim_pages (only if CONFIG_MMU=n)
- numa_zonelist_order
- oom_dump_tasks
@@ -426,16 +425,6 @@ See Documentation/vm/hugetlbpage.txt

==============================================================

-nr_pdflush_threads
-
-The current number of pdflush threads. This value is read-only.
-The value changes according to the number of dirty pages in the system.
-
-When necessary, additional pdflush threads are created, one per second, up to
-nr_pdflush_threads_max.
-
-==============================================================
-
nr_trim_pages

This is available only on NOMMU kernels.
diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index d462fe7..37e9ced 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -52,11 +52,6 @@ struct wb_writeback_work {
struct completion *done; /* set if the caller waits */
};

-/*
- * We don't actually have pdflush, but this one is exported though /proc...
- */
-int nr_pdflush_threads;
-
/**
* writeback_in_progress - determine whether there is writeback in progress
* @bdi: the device's backing_dev_info structure.
diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
index b1038bd..db7a5ab 100644
--- a/include/linux/backing-dev.h
+++ b/include/linux/backing-dev.h
@@ -17,6 +17,7 @@
#include <linux/timer.h>
#include <linux/writeback.h>
#include <linux/atomic.h>
+#include <linux/sysctl.h>

struct page;
struct device;
@@ -304,6 +305,8 @@ void clear_bdi_congested(struct backing_dev_info *bdi, int sync);
void set_bdi_congested(struct backing_dev_info *bdi, int sync);
long congestion_wait(int sync, long timeout);
long wait_iff_congested(struct zone *zone, int sync, long timeout);
+int pdflush_proc_obsolete(struct ctl_table *table, int write,
+ void __user *buffer, size_t *lenp, loff_t *ppos);

static inline bool bdi_cap_writeback_dirty(struct backing_dev_info *bdi)
{
diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index 6d0a0fc..c66fe33 100644
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -189,9 +189,4 @@ void tag_pages_for_writeback(struct address_space *mapping,

void account_page_redirty(struct page *page);

-/* pdflush.c */
-extern int nr_pdflush_threads; /* Global so it can be exported to sysctl
- read-only. */
-
-
#endif /* WRITEBACK_H */
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 4ab1187..b3b9ba4 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -1095,11 +1095,9 @@ 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 a650694..65bdcf1 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 */
diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index dd8e2aa..e9caa10 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -886,3 +886,23 @@ out:
return ret;
}
EXPORT_SYMBOL(wait_iff_congested);
+
+int pdflush_proc_obsolete(struct ctl_table *table, int write,
+ void __user *buffer, size_t *lenp, loff_t *ppos)
+{
+ char kbuf[] = "0\n";
+
+ if (*ppos) {
+ *lenp = 0;
+ return 0;
+ }
+
+ if (copy_to_user(buffer, kbuf, sizeof(kbuf)))
+ return -EFAULT;
+ printk_once(KERN_WARNING "%s exported in /proc is scheduled for removal\n",
+ table->procname);
+
+ *lenp = 2;
+ *ppos += *lenp;
+ return 0;
+}
--
1.7.9.5

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