[Patch 2/8] Sync block I/O and swapin delay collection

[Shailabh Nagar <nagar@watson.ibm.com>]

Changelog

Fixes comments by akpm
- avoid creating new per-process flag PF_SWAPIN

delayacct-blkio-swapin.patch

Collect per-task block I/O delay statistics.

Unlike earlier iterations of the delay accounting
patches, now delays are only collected for the actual
I/O waits rather than try and cover the delays seen in
I/O submission paths.

Account separately for block I/O delays
incurred as a result of swapin page faults whose
frequency can be affected by the task/process' rss limit.
Hence swapin delays can act as feedback for rss limit changes
independent of I/O priority changes.

Signed-off-by: Shailabh Nagar <nagar@watson.ibm.com>

 include/linux/delayacct.h |   25 +++++++++++++++++++++++++
 include/linux/sched.h     |    6 ++++++
 kernel/delayacct.c        |   19 +++++++++++++++++++
 kernel/sched.c            |    5 +++++
 mm/memory.c               |    4 ++++
 5 files changed, 59 insertions(+)

Index: linux-2.6.17-rc1/include/linux/delayacct.h
===================================================================
--- linux-2.6.17-rc1.orig/include/linux/delayacct.h	2006-04-21 22:27:18.000000000 -0400
+++ linux-2.6.17-rc1/include/linux/delayacct.h	2006-04-21 22:27:19.000000000 -0400
@@ -19,6 +19,13 @@

 #include <linux/sched.h>

+/*
+ * Per-task flags relevant to delay accounting
+ * maintained privately to avoid exhausting similar flags in sched.h:PF_*
+ * Used to set current->delays->flags
+ */
+#define DELAYACCT_PF_SWAPIN	0x00000001	/* I am doing a swapin */
+
 #ifdef CONFIG_TASK_DELAY_ACCT

 extern int delayacct_on;	/* Delay accounting turned on/off */
@@ -26,6 +33,8 @@ extern kmem_cache_t *delayacct_cache;
 extern void delayacct_init(void);
 extern void __delayacct_tsk_init(struct task_struct *);
 extern void __delayacct_tsk_exit(struct task_struct *);
+extern void __delayacct_blkio_start(void);
+extern void __delayacct_blkio_end(void);

 static inline void delayacct_set_flag(int flag)
 {
@@ -53,6 +62,18 @@ static inline void delayacct_tsk_exit(st
 		__delayacct_tsk_exit(tsk);
 }

+static inline void delayacct_blkio_start(void)
+{
+	if (current->delays)
+		__delayacct_blkio_start();
+}
+
+static inline void delayacct_blkio_end(void)
+{
+	if (current->delays)
+		__delayacct_blkio_end();
+}
+
 #else
 static inline void delayacct_set_flag(int flag)
 {}
@@ -64,6 +85,10 @@ static inline void delayacct_tsk_init(st
 {}
 static inline void delayacct_tsk_exit(struct task_struct *tsk)
 {}
+static inline void delayacct_blkio_start(void)
+{}
+static inline void delayacct_blkio_end(void)
+{}
 #endif /* CONFIG_TASK_DELAY_ACCT */

 #endif
Index: linux-2.6.17-rc1/kernel/delayacct.c
===================================================================
--- linux-2.6.17-rc1.orig/kernel/delayacct.c	2006-04-21 22:27:18.000000000 -0400
+++ linux-2.6.17-rc1/kernel/delayacct.c	2006-04-21 22:27:19.000000000 -0400
@@ -85,3 +85,22 @@ static inline void delayacct_end(struct
 	spin_unlock(&current->delays->lock);
 }

+void __delayacct_blkio_start(void)
+{
+	delayacct_start(&current->delays->blkio_start);
+}
+
+void __delayacct_blkio_end(void)
+{
+	if (current->delays->flags & DELAYACCT_PF_SWAPIN)
+		/* Swapin block I/O */
+		delayacct_end(&current->delays->blkio_start,
+			      &current->delays->blkio_end,
+			      &current->delays->swapin_delay,
+			      &current->delays->swapin_count);
+	else	/* Other block I/O */
+		delayacct_end(&current->delays->blkio_start,
+			      &current->delays->blkio_end,
+			      &current->delays->blkio_delay,
+			      &current->delays->blkio_count);
+}
Index: linux-2.6.17-rc1/include/linux/sched.h
===================================================================
--- linux-2.6.17-rc1.orig/include/linux/sched.h	2006-04-21 22:27:18.000000000 -0400
+++ linux-2.6.17-rc1/include/linux/sched.h	2006-04-21 22:27:19.000000000 -0400
@@ -550,6 +550,12 @@ struct task_delay_info {
 	 * Atomicity of updates to XXX_delay, XXX_count protected by
 	 * single lock above (split into XXX_lock if contention is an issue).
 	 */
+
+	struct timespec blkio_start, blkio_end;	/* Shared by blkio, swapin */
+	u64 blkio_delay;	/* wait for sync block io completion */
+	u64 swapin_delay;	/* wait for swapin block io completion */
+	u32 blkio_count;
+	u32 swapin_count;
 };
 #endif

Index: linux-2.6.17-rc1/kernel/sched.c
===================================================================
--- linux-2.6.17-rc1.orig/kernel/sched.c	2006-04-21 22:27:18.000000000 -0400
+++ linux-2.6.17-rc1/kernel/sched.c	2006-04-21 22:27:19.000000000 -0400
@@ -50,6 +50,7 @@
 #include <linux/times.h>
 #include <linux/acct.h>
 #include <linux/kprobes.h>
+#include <linux/delayacct.h>
 #include <asm/tlb.h>

 #include <asm/unistd.h>
@@ -4144,9 +4145,11 @@ void __sched io_schedule(void)
 {
 	struct runqueue *rq = &per_cpu(runqueues, raw_smp_processor_id());

+	delayacct_blkio_start();
 	atomic_inc(&rq->nr_iowait);
 	schedule();
 	atomic_dec(&rq->nr_iowait);
+	delayacct_blkio_end();
 }

 EXPORT_SYMBOL(io_schedule);
@@ -4156,9 +4159,11 @@ long __sched io_schedule_timeout(long ti
 	struct runqueue *rq = &per_cpu(runqueues, raw_smp_processor_id());
 	long ret;

+	delayacct_blkio_start();
 	atomic_inc(&rq->nr_iowait);
 	ret = schedule_timeout(timeout);
 	atomic_dec(&rq->nr_iowait);
+	delayacct_blkio_end();
 	return ret;
 }

Index: linux-2.6.17-rc1/mm/memory.c
===================================================================
--- linux-2.6.17-rc1.orig/mm/memory.c	2006-04-21 22:27:18.000000000 -0400
+++ linux-2.6.17-rc1/mm/memory.c	2006-04-21 22:27:19.000000000 -0400
@@ -48,6 +48,7 @@
 #include <linux/rmap.h>
 #include <linux/module.h>
 #include <linux/init.h>
+#include <linux/delayacct.h>

 #include <asm/pgalloc.h>
 #include <asm/uaccess.h>
@@ -1880,6 +1881,7 @@ static int do_swap_page(struct mm_struct

 	entry = pte_to_swp_entry(orig_pte);
 again:
+	delayacct_set_flag(DELAYACCT_PF_SWAPIN);
 	page = lookup_swap_cache(entry);
 	if (!page) {
  		swapin_readahead(entry, address, vma);
@@ -1892,6 +1894,7 @@ again:
 			page_table = pte_offset_map_lock(mm, pmd, address, &ptl);
 			if (likely(pte_same(*page_table, orig_pte)))
 				ret = VM_FAULT_OOM;
+			delayacct_clear_flag(DELAYACCT_PF_SWAPIN);
 			goto unlock;
 		}

@@ -1903,6 +1906,7 @@ again:

 	mark_page_accessed(page);
 	lock_page(page);
+	delayacct_clear_flag(DELAYACCT_PF_SWAPIN);
 	if (!PageSwapCache(page)) {
 		/* Page migration has occured */
 		unlock_page(page);