Re: [PATCH v2] remove no longer use of pdflush interface

[Gavin Shan <shangw@linux.vnet.ibm.com>]

Hi WanPeng,

I have 2 questions here.

- Why not just remove the proc entry since we needn't it anymore?
- If we really want to keep the entry and just output warning message, we *only*
  can see the message out of system console. It's reasonable to put the message
  into the buffer directly so that any users from system console/telnet/ssh can
  see the warning message?

Thanks,
Gavin

>From: Wanpeng Li <liwp@linux.vnet.ibm.com>
>
>------------------
>
>Change in v2:
>
>* add printk warning
>* add description in Documentation
>
>------------------
>
>Signed-off-by: Wanpeng Li <liwp@linux.vnet.ibm.com>
>---
> .../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/sysctl.h                             |    3 +++
> include/linux/writeback.h                          |    5 -----
> kernel/sysctl.c                                    |   18 +++++++++++++-----
> kernel/sysctl_binary.c                             |    2 +-
> 8 files changed, 30 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..edbe548
>--- /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@linux.vnet.ibm.com>
>+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 e4b5775..7eea1ee 100644
>--- a/Documentation/feature-removal-schedule.txt
>+++ b/Documentation/feature-removal-schedule.txt
>@@ -6,6 +6,14 @@ be removed from this file.
>
> ---------------------------
>
>+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@linux.vnet.ibm.com>
>+
>+---------------------------
>+
> 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 539f36c..30ddb8a 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/sysctl.h b/include/linux/sysctl.h
>index c34b4c8..f25be74 100644
>--- a/include/linux/sysctl.h
>+++ b/include/linux/sysctl.h
>@@ -964,6 +964,9 @@ extern int proc_doulongvec_ms_jiffies_minmax(struct ctl_table *table, int,
> 				      void __user *, size_t *, loff_t *);
> extern int proc_do_large_bitmap(struct ctl_table *, int,
> 				void __user *, size_t *, loff_t *);
>+extern int proc_deprecated(struct ctl_table *, int,
>+				void __user *, size_t *, loff_t *);
>+
>
> /*
>  * Register a set of sysctl names by calling register_sysctl_table
>diff --git a/include/linux/writeback.h b/include/linux/writeback.h
>index a2b84f5..13b5df7 100644
>--- a/include/linux/writeback.h
>+++ b/include/linux/writeback.h
>@@ -193,9 +193,4 @@ 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..1ab53cb 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   = proc_deprecated,
> 	},
> 	{
> 		.procname	= "swappiness",
>@@ -2505,6 +2503,15 @@ int proc_doulongvec_ms_jiffies_minmax(struct ctl_table *table, int write,
>
> #endif /* CONFIG_PROC_SYSCTL */
>
>+/* notice associated proc deprecated */
>+int proc_deprecated(struct ctl_table *table, int write,
>+		    void __user *buffer, size_t *lenp, loff_t *ppos)
>+{
>+	printk(KERN_WARNING "%s exported in /proc is deprecated\n",
>+			table->procname);
>+	return -ENOSYS;
>+}
>+
> /*
>  * No sense putting this after each symbol definition, twice,
>  * exception granted :-)
>@@ -2517,3 +2524,4 @@ EXPORT_SYMBOL(proc_dointvec_ms_jiffies);
> EXPORT_SYMBOL(proc_dostring);
> EXPORT_SYMBOL(proc_doulongvec_minmax);
> EXPORT_SYMBOL(proc_doulongvec_ms_jiffies_minmax);
>+EXPORT_SYMBOL(proc_deprecated);
>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 */
>-- 
>1.7.9.5
>