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Subject[Patch 2/8] Sync block I/O and swapin delay collection
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);
-
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