[PATCH] per-task-delay-accounting: sync block I/O and swapin delay collection

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>
Signed-off-by: Balbir Singh <balbir@in.ibm.com>
Cc: Jes Sorensen <jes@sgi.com>
Cc: Peter Chubb <peterc@gelato.unsw.edu.au>
Cc: Erich Focht <efocht@ess.nec.de>
Cc: Levent Serinol <lserinol@gmail.com>
Cc: Jay Lan <jlan@engr.sgi.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

include/linux/delayacct.h

@@ -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(struct task_struct *tsk)
 		__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(struct task_struct *tsk)
 {}
 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

include/linux/sched.h

@@ -566,6 +566,19 @@ 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).
 	 */
+
+	/*
+	 * XXX_count is incremented on every XXX operation, the delay
+	 * associated with the operation is added to XXX_delay.
+	 * XXX_delay contains the accumulated delay time in nanoseconds.
+	 */
+	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;	/* total count of the number of sync block */
+				/* io operations performed */
+	u32 swapin_count;	/* total count of the number of swapin block */
+				/* io operations performed */
 };
 #endif
 

kernel/delayacct.c

@@ -85,3 +85,22 @@ static void delayacct_end(struct timespec *start, struct timespec *end,
 	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);
+}

kernel/sched.c

@@ -51,6 +51,7 @@
 #include <linux/times.h>
 #include <linux/acct.h>
 #include <linux/kprobes.h>
+#include <linux/delayacct.h>
 #include <asm/tlb.h>
 
 #include <asm/unistd.h>
@@ -4534,9 +4535,11 @@ void __sched io_schedule(void)
 {
 	struct rq *rq = &__raw_get_cpu_var(runqueues);
 
+	delayacct_blkio_start();
 	atomic_inc(&rq->nr_iowait);
 	schedule();
 	atomic_dec(&rq->nr_iowait);
+	delayacct_blkio_end();
 }
 EXPORT_SYMBOL(io_schedule);
 
@@ -4545,9 +4548,11 @@ long __sched io_schedule_timeout(long timeout)
 	struct rq *rq = &__raw_get_cpu_var(runqueues);
 	long ret;
 
+	delayacct_blkio_start();
 	atomic_inc(&rq->nr_iowait);
 	ret = schedule_timeout(timeout);
 	atomic_dec(&rq->nr_iowait);
+	delayacct_blkio_end();
 	return ret;
 }
 

mm/memory.c

@@ -47,6 +47,7 @@
 #include <linux/pagemap.h>
 #include <linux/rmap.h>
 #include <linux/module.h>
+#include <linux/delayacct.h>
 #include <linux/init.h>
 
 #include <asm/pgalloc.h>
@@ -1934,6 +1935,7 @@ static int do_swap_page(struct mm_struct *mm, struct vm_area_struct *vma,
 		migration_entry_wait(mm, pmd, address);
 		goto out;
 	}
+	delayacct_set_flag(DELAYACCT_PF_SWAPIN);
 	page = lookup_swap_cache(entry);
 	if (!page) {
  		swapin_readahead(entry, address, vma);
@@ -1946,6 +1948,7 @@ static int do_swap_page(struct mm_struct *mm, struct vm_area_struct *vma,
 			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;
 		}
 
@@ -1955,6 +1958,7 @@ static int do_swap_page(struct mm_struct *mm, struct vm_area_struct *vma,
 		grab_swap_token();
 	}
 
+	delayacct_clear_flag(DELAYACCT_PF_SWAPIN);
 	mark_page_accessed(page);
 	lock_page(page);