Writeback/pdflush cleanup patch from Steven Augart
* Exposes nr_pdflush_threads as /proc/sys/vm/nr_pdflush_threads, read-only.
(I like this - I expect that management of the pdflush thread pool
will be important for many-spindle machines, and this is a neat way
of getting at the info).
* Adds minimum and maximum checking to the five writable pdflush
and fs-writeback parameters.
* Minor indentation fix in sysctl.c
* mm/pdflush.c now includes linux/writeback.h, which prototypes
pdflush_operation. This is so that the compiler can
automatically check that the prototype matches the definition.
* Adds a few comments to existing code.
include/linux/sysctl.h | 6 +++++-
include/linux/writeback.h | 7 +++++++
kernel/sysctl.c | 42 ++++++++++++++++++++++++++++++++++--------
mm/page-writeback.c | 12 +++++++++---
mm/pdflush.c | 8 +++++++-
5 files changed, 62 insertions(+), 13 deletions(-)
--- 2.5.24/include/linux/sysctl.h~pdflush-cleanup Thu Jul 4 16:17:14 2002
+++ 2.5.24-akpm/include/linux/sysctl.h Thu Jul 4 16:17:14 2002
@@ -30,7 +30,10 @@
struct file;
-#define CTL_MAXNAME 10
+#define CTL_MAXNAME 10 /* how many path components do we allow in a
+ call to sysctl? In other words, what is
+ the largest acceptable value for the nlen
+ member of a struct __sysctl_args to have? */
struct __sysctl_args {
int *name;
@@ -145,6 +148,7 @@ enum
VM_DIRTY_SYNC=13, /* dirty_sync_ratio */
VM_DIRTY_WB_CS=14, /* dirty_writeback_centisecs */
VM_DIRTY_EXPIRE_CS=15, /* dirty_expire_centisecs */
+ VM_NR_PDFLUSH_THREADS=16, /* nr_pdflush_threads */
};
--- 2.5.24/include/linux/writeback.h~pdflush-cleanup Thu Jul 4 16:17:14 2002
+++ 2.5.24-akpm/include/linux/writeback.h Thu Jul 4 16:17:14 2002
@@ -49,15 +49,22 @@ static inline void wait_on_inode(struct
/*
* mm/page-writeback.c
*/
+/* These 5 are exported to sysctl. */
extern int dirty_background_ratio;
extern int dirty_async_ratio;
extern int dirty_sync_ratio;
extern int dirty_writeback_centisecs;
extern int dirty_expire_centisecs;
+
void balance_dirty_pages(struct address_space *mapping);
void balance_dirty_pages_ratelimited(struct address_space *mapping);
int pdflush_operation(void (*fn)(unsigned long), unsigned long arg0);
int do_writepages(struct address_space *mapping, int *nr_to_write);
+/* pdflush.c */
+extern int nr_pdflush_threads; /* Global so it can be exported to sysctl
+ read-only. */
+
+
#endif /* WRITEBACK_H */
--- 2.5.24/kernel/sysctl.c~pdflush-cleanup Thu Jul 4 16:17:14 2002
+++ 2.5.24-akpm/kernel/sysctl.c Thu Jul 4 16:17:14 2002
@@ -258,6 +258,13 @@ static ctl_table kern_table[] = {
{0}
};
+/* Constants for minimum and maximum testing in vm_table.
+ We use these as one-element integer vectors. */
+static int zero = 0;
+static int one = 1;
+static int one_hundred = 100;
+
+
static ctl_table vm_table[] = {
{VM_OVERCOMMIT_MEMORY, "overcommit_memory", &sysctl_overcommit_memory,
sizeof(sysctl_overcommit_memory), 0644, NULL, &proc_dointvec},
@@ -266,18 +273,37 @@ static ctl_table vm_table[] = {
{VM_PAGE_CLUSTER, "page-cluster",
&page_cluster, sizeof(int), 0644, NULL, &proc_dointvec},
{VM_DIRTY_BACKGROUND, "dirty_background_ratio",
- &dirty_background_ratio, sizeof(dirty_background_ratio),
- 0644, NULL, &proc_dointvec},
+ &dirty_background_ratio, sizeof(dirty_background_ratio),
+ 0644, NULL, &proc_dointvec_minmax, &sysctl_intvec, NULL,
+ &zero, &one_hundred },
{VM_DIRTY_ASYNC, "dirty_async_ratio", &dirty_async_ratio,
- sizeof(dirty_async_ratio), 0644, NULL, &proc_dointvec},
+ sizeof(dirty_async_ratio), 0644, NULL, &proc_dointvec_minmax,
+ &sysctl_intvec, NULL, &zero, &one_hundred },
{VM_DIRTY_SYNC, "dirty_sync_ratio", &dirty_sync_ratio,
- sizeof(dirty_sync_ratio), 0644, NULL, &proc_dointvec},
+ sizeof(dirty_sync_ratio), 0644, NULL, &proc_dointvec_minmax,
+ &sysctl_intvec, NULL, &zero, &one_hundred },
{VM_DIRTY_WB_CS, "dirty_writeback_centisecs",
- &dirty_writeback_centisecs, sizeof(dirty_writeback_centisecs), 0644,
- NULL, &proc_dointvec},
+ &dirty_writeback_centisecs, sizeof(dirty_writeback_centisecs), 0644,
+ NULL, &proc_dointvec_minmax, &sysctl_intvec, NULL,
+ /* Here, we define the range of possible values for
+ dirty_writeback_centisecs.
+
+ The default value is 5 seconds (500 centisec). We will use 1
+ centisec, the smallest possible value that could make any sort of
+ sense. If we allowed the user to set the interval to 0 seconds
+ (which would presumably mean to chew up all of the CPU looking for
+ dirty pages and writing them out, without taking a break), the
+ interval would effectively become 1 second (100 centisecs), due to
+ some nicely documented throttling code in wb_kupdate().
+
+ There is no maximum legal value for dirty_writeback. */
+ &one , NULL},
{VM_DIRTY_EXPIRE_CS, "dirty_expire_centisecs",
- &dirty_expire_centisecs, sizeof(dirty_expire_centisecs), 0644,
- NULL, &proc_dointvec},
+ &dirty_expire_centisecs, sizeof(dirty_expire_centisecs), 0644,
+ NULL, &proc_dointvec},
+ { VM_NR_PDFLUSH_THREADS, "nr_pdflush_threads",
+ &nr_pdflush_threads, sizeof nr_pdflush_threads,
+ 0444 /* read-only*/, NULL, &proc_dointvec},
{0}
};
--- 2.5.24/mm/page-writeback.c~pdflush-cleanup Thu Jul 4 16:17:14 2002
+++ 2.5.24-akpm/mm/page-writeback.c Thu Jul 4 16:22:08 2002
@@ -47,6 +47,8 @@
#define SYNC_WRITEBACK_PAGES 1500
+/* The following parameters are exported via /proc/sys/vm */
+
/*
* Dirty memory thresholds, in percentages
*/
@@ -67,15 +69,18 @@ int dirty_async_ratio = 50;
int dirty_sync_ratio = 60;
/*
- * The interval between `kupdate'-style writebacks.
+ * The interval between `kupdate'-style writebacks, in centiseconds
+ * (hundredths of a second)
*/
int dirty_writeback_centisecs = 5 * 100;
/*
- * The largest amount of time for which data is allowed to remain dirty
+ * The longest amount of time for which data is allowed to remain dirty
*/
int dirty_expire_centisecs = 30 * 100;
+/* End of sysctl-exported parameters */
+
static void background_writeout(unsigned long _min_pages);
@@ -233,7 +238,8 @@ static void wb_kupdate(unsigned long arg
static void wb_timer_fn(unsigned long unused)
{
if (pdflush_operation(wb_kupdate, 0) < 0)
- mod_timer(&wb_timer, jiffies + HZ);
+ mod_timer(&wb_timer, jiffies + HZ); /* delay 1 second */
+
}
static int __init wb_timer_init(void)
--- 2.5.24/mm/pdflush.c~pdflush-cleanup Thu Jul 4 16:17:14 2002
+++ 2.5.24-akpm/mm/pdflush.c Thu Jul 4 16:17:14 2002
@@ -15,6 +15,9 @@
#include <linux/init.h>
#include <linux/module.h>
#include <linux/suspend.h>
+#include <linux/sched.h> // Needed by writeback.h
+#include <linux/fs.h> // Needed by writeback.h
+#include <linux/writeback.h> // Prototypes pdflush_operation()
/*
@@ -44,8 +47,11 @@ static spinlock_t pdflush_lock = SPIN_LO
/*
* The count of currently-running pdflush threads. Protected
* by pdflush_lock.
+ *
+ * Readable by sysctl, but not writable. Published to userspace at
+ * /proc/sys/vm/nr_pdflush_threads.
*/
-static int nr_pdflush_threads = 0;
+int nr_pdflush_threads = 0;
/*
* The time at which the pdflush thread pool last went empty
-
-
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