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    SubjectRe: [PATCH v2] remove no longer use of pdflush interface
    On Tue, Jun 05, 2012 at 10:45:20PM +0800, Gavin Shan wrote:

    Hi Gavin,

    >
    >- Why not just remove the proc entry since we needn't it anymore?

    Some user applications maybe still use this interface, so we should take
    attention to back-compatibility issues.

    >- 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?

    Maybe this is a good idea.

    >
    >>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
    >>
    >
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