[Patch 2/8] Block I/O, swapin delays

From: Shailabh Nagar
Date: Wed Mar 29 2006 - 19:34:27 EST

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@xxxxxxxxxxxxxx>

include/linux/delayacct.h | 16 ++++++++++++++++
include/linux/sched.h | 7 +++++++
kernel/delayacct.c | 18 ++++++++++++++++++
kernel/sched.c | 5 +++++
mm/memory.c | 4 ++++
5 files changed, 50 insertions(+)

Index: linux-2.6.16/include/linux/delayacct.h
===================================================================
--- linux-2.6.16.orig/include/linux/delayacct.h 2006-03-29 18:12:57.000000000 -0500
+++ linux-2.6.16/include/linux/delayacct.h 2006-03-29 18:13:13.000000000 -0500
@@ -25,6 +25,8 @@ 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_tsk_init(struct task_struct *tsk)
{
@@ -40,6 +42,16 @@ 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_init(void)
{}
@@ -47,5 +59,9 @@ 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 /* _LINUX_TASKDELAYS_H */
Index: linux-2.6.16/kernel/delayacct.c
===================================================================
--- linux-2.6.16.orig/kernel/delayacct.c 2006-03-29 18:12:57.000000000 -0500
+++ linux-2.6.16/kernel/delayacct.c 2006-03-29 18:13:13.000000000 -0500
@@ -90,3 +90,21 @@ 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->flags & PF_SWAPIN) /* Swapping a page in */
+ 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-2.6.16/include/linux/sched.h
===================================================================
--- linux-2.6.16.orig/include/linux/sched.h 2006-03-29 18:12:57.000000000 -0500
+++ linux-2.6.16/include/linux/sched.h 2006-03-29 18:13:13.000000000 -0500
@@ -550,6 +550,12 @@ struct task_delay_info {
* u64 XXX_delay;
* u32 XXX_count;
*/
+
+ struct timespec blkio_start, blkio_end; /* Shared by blkio, swapin */
+ u64 blkio_delay; /* wait for sync block io completion */
+ u64 swapin_delay; /* wait for sync block io completion */
+ u32 blkio_count;
+ u32 swapin_count;
};
#endif

@@ -945,6 +951,7 @@ static inline void put_task_struct(struc
#define PF_BORROWED_MM 0x00400000 /* I am a kthread doing use_mm */
#define PF_RANDOMIZE 0x00800000 /* randomize virtual address space */
#define PF_SWAPWRITE 0x01000000 /* Allowed to write to swap */
+#define PF_SWAPIN 0x02000000 /* I am doing a swap in */

/*
* Only the _current_ task can read/write to tsk->flags, but other
Index: linux-2.6.16/kernel/sched.c
===================================================================
--- linux-2.6.16.orig/kernel/sched.c 2006-03-29 18:12:54.000000000 -0500
+++ linux-2.6.16/kernel/sched.c 2006-03-29 18:13:13.000000000 -0500
@@ -49,6 +49,7 @@
#include <linux/syscalls.h>
#include <linux/times.h>
#include <linux/acct.h>
+#include <linux/delayacct.h>
#include <asm/tlb.h>

#include <asm/unistd.h>
@@ -4112,9 +4113,11 @@ 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);
@@ -4124,9 +4127,11 @@ 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-2.6.16/mm/memory.c
===================================================================
--- linux-2.6.16.orig/mm/memory.c 2006-03-29 18:12:54.000000000 -0500
+++ linux-2.6.16/mm/memory.c 2006-03-29 18:13:13.000000000 -0500
@@ -1883,6 +1883,7 @@ static int do_swap_page(struct mm_struct

entry = pte_to_swp_entry(orig_pte);
again:
+ current->flags |= PF_SWAPIN;
page = lookup_swap_cache(entry);
if (!page) {
swapin_readahead(entry, address, vma);
@@ -1895,6 +1896,7 @@ again:
page_table = pte_offset_map_lock(mm, pmd, address, &ptl);
if (likely(pte_same(*page_table, orig_pte)))
ret = VM_FAULT_OOM;
+ current->flags &= ~PF_SWAPIN;
goto unlock;
}

@@ -1906,6 +1908,8 @@ again:

mark_page_accessed(page);
lock_page(page);
+ current->flags &= ~PF_SWAPIN;
+
if (!PageSwapCache(page)) {
/* Page migration has occured */
unlock_page(page);
-
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