[PATCH] delayacct: track delays from write-protect copy

From: cgel . zte
Date: Fri Apr 08 2022 - 06:38:53 EST

From: Yang Yang <yang.yang29@xxxxxxxxxx>

Delay accounting does not track the delay of write-protect copy. When
tasks trigger many write-protect copys(include COW and unsharing of
anonymous pages[1]), it may spend a amount of time waiting for them.
To get the delay of tasks in write-protect copy, could help users to
evaluate the impact of using KSM or fork() or GUP.

Also update tools/accounting/getdelays.c:

/ # ./getdelays -dl -p 231
print delayacct stats ON
listen forever
PID 231

CPU count real total virtual total delay total delay average
6247 1859000000 2154070021 1674255063 0.268ms
IO count delay total delay average
0 0 0ms
SWAP count delay total delay average
0 0 0ms
RECLAIM count delay total delay average
0 0 0ms
THRASHING count delay total delay average
0 0 0ms
COMPACT count delay total delay average
3 72758 0ms
WPCOPY count delay total delay average
3635 271567604 0ms

[1] commit 31cc5bc4af70("mm: support GUP-triggered unsharing of anonymous pages")

Signed-off-by: Yang Yang <yang.yang29@xxxxxxxxxx>
Reviewed-by: David Hildenbrand <david@xxxxxxxxxx>
Reviewed-by: Jiang Xuexin <jiang.xuexin@xxxxxxxxxx>
Reviewed-by: Ran Xiaokai <ran.xiaokai@xxxxxxxxxx>
Reviewed-by: wangyong <wang.yong12@xxxxxxxxxx>
---
Documentation/accounting/delay-accounting.rst | 5 +++-
include/linux/delayacct.h | 28 +++++++++++++++++++
include/uapi/linux/taskstats.h | 6 +++-
kernel/delayacct.c | 16 +++++++++++
mm/hugetlb.c | 7 +++++
mm/memory.c | 8 ++++++
tools/accounting/getdelays.c | 8 +++++-
7 files changed, 75 insertions(+), 3 deletions(-)

diff --git a/Documentation/accounting/delay-accounting.rst b/Documentation/accounting/delay-accounting.rst
index 197fe319cbec..241d1a87f2cd 100644
--- a/Documentation/accounting/delay-accounting.rst
+++ b/Documentation/accounting/delay-accounting.rst
@@ -15,6 +15,7 @@ c) swapping in pages
d) memory reclaim
e) thrashing page cache
f) direct compact
+g) write-protect copy

and makes these statistics available to userspace through
the taskstats interface.
@@ -48,7 +49,7 @@ this structure. See
for a description of the fields pertaining to delay accounting.
It will generally be in the form of counters returning the cumulative
delay seen for cpu, sync block I/O, swapin, memory reclaim, thrash page
-cache, direct compact etc.
+cache, direct compact, write-protect copy etc.

Taking the difference of two successive readings of a given
counter (say cpu_delay_total) for a task will give the delay
@@ -117,6 +118,8 @@ Get sum of delays, since system boot, for all pids with tgid 5::
0 0 0ms
COMPACT count delay total delay average
0 0 0ms
+ WPCOPY count delay total delay average
+ 0 0 0ms

Get IO accounting for pid 1, it works only with -p::

diff --git a/include/linux/delayacct.h b/include/linux/delayacct.h
index 6b16a6930a19..58aea2d7385c 100644
--- a/include/linux/delayacct.h
+++ b/include/linux/delayacct.h
@@ -45,9 +45,13 @@ struct task_delay_info {
u64 compact_start;
u64 compact_delay; /* wait for memory compact */

+ u64 wpcopy_start;
+ u64 wpcopy_delay; /* wait for write-protect copy */
+
u32 freepages_count; /* total count of memory reclaim */
u32 thrashing_count; /* total count of thrash waits */
u32 compact_count; /* total count of memory compact */
+ u32 wpcopy_count; /* total count of write-protect copy */
};
#endif

@@ -75,6 +79,8 @@ extern void __delayacct_swapin_start(void);
extern void __delayacct_swapin_end(void);
extern void __delayacct_compact_start(void);
extern void __delayacct_compact_end(void);
+extern void __delayacct_wpcopy_start(void);
+extern void __delayacct_wpcopy_end(void);

static inline void delayacct_tsk_init(struct task_struct *tsk)
{
@@ -191,6 +197,24 @@ static inline void delayacct_compact_end(void)
__delayacct_compact_end();
}

+static inline void delayacct_wpcopy_start(void)
+{
+ if (!static_branch_unlikely(&delayacct_key))
+ return;
+
+ if (current->delays)
+ __delayacct_wpcopy_start();
+}
+
+static inline void delayacct_wpcopy_end(void)
+{
+ if (!static_branch_unlikely(&delayacct_key))
+ return;
+
+ if (current->delays)
+ __delayacct_wpcopy_end();
+}
+
#else
static inline void delayacct_init(void)
{}
@@ -225,6 +249,10 @@ static inline void delayacct_compact_start(void)
{}
static inline void delayacct_compact_end(void)
{}
+static inline void delayacct_wpcopy_start(void)
+{}
+static inline void delayacct_wpcopy_end(void)
+{}

#endif /* CONFIG_TASK_DELAY_ACCT */

diff --git a/include/uapi/linux/taskstats.h b/include/uapi/linux/taskstats.h
index 736154171489..a7f5b11a8f1b 100644
--- a/include/uapi/linux/taskstats.h
+++ b/include/uapi/linux/taskstats.h
@@ -34,7 +34,7 @@
*/


-#define TASKSTATS_VERSION 12
+#define TASKSTATS_VERSION 13
#define TS_COMM_LEN 32 /* should be >= TASK_COMM_LEN
* in linux/sched.h */

@@ -194,6 +194,10 @@ struct taskstats {
__u64 ac_exe_dev; /* program binary device ID */
__u64 ac_exe_inode; /* program binary inode number */
/* v12 end */
+
+ /* v13: Delay waiting for write-protect copy */
+ __u64 wpcopy_count;
+ __u64 wpcopy_delay_total;
};


diff --git a/kernel/delayacct.c b/kernel/delayacct.c
index 2c1e18f7c5cf..164ed9ef77a3 100644
--- a/kernel/delayacct.c
+++ b/kernel/delayacct.c
@@ -177,11 +177,14 @@ int delayacct_add_tsk(struct taskstats *d, struct task_struct *tsk)
d->thrashing_delay_total = (tmp < d->thrashing_delay_total) ? 0 : tmp;
tmp = d->compact_delay_total + tsk->delays->compact_delay;
d->compact_delay_total = (tmp < d->compact_delay_total) ? 0 : tmp;
+ tmp = d->wpcopy_delay_total + tsk->delays->wpcopy_delay;
+ d->wpcopy_delay_total = (tmp < d->wpcopy_delay_total) ? 0 : tmp;
d->blkio_count += tsk->delays->blkio_count;
d->swapin_count += tsk->delays->swapin_count;
d->freepages_count += tsk->delays->freepages_count;
d->thrashing_count += tsk->delays->thrashing_count;
d->compact_count += tsk->delays->compact_count;
+ d->wpcopy_count += tsk->delays->wpcopy_count;
raw_spin_unlock_irqrestore(&tsk->delays->lock, flags);

return 0;
@@ -249,3 +252,16 @@ void __delayacct_compact_end(void)
&current->delays->compact_delay,
&current->delays->compact_count);
}
+
+void __delayacct_wpcopy_start(void)
+{
+ current->delays->wpcopy_start = local_clock();
+}
+
+void __delayacct_wpcopy_end(void)
+{
+ delayacct_end(&current->delays->lock,
+ &current->delays->wpcopy_start,
+ &current->delays->wpcopy_delay,
+ &current->delays->wpcopy_count);
+}
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index fb5a549169ce..b131d44741dd 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -5173,6 +5173,8 @@ static vm_fault_t hugetlb_wp(struct mm_struct *mm, struct vm_area_struct *vma,
pte = huge_ptep_get(ptep);
old_page = pte_page(pte);

+ delayacct_wpcopy_start();
+
retry_avoidcopy:
/*
* If no-one else is actually using this page, we're the exclusive
@@ -5183,6 +5185,8 @@ static vm_fault_t hugetlb_wp(struct mm_struct *mm, struct vm_area_struct *vma,
page_move_anon_rmap(old_page, vma);
if (likely(!unshare))
set_huge_ptep_writable(vma, haddr, ptep);
+
+ delayacct_wpcopy_end();
return 0;
}
VM_BUG_ON_PAGE(PageAnon(old_page) && PageAnonExclusive(old_page),
@@ -5252,6 +5256,7 @@ static vm_fault_t hugetlb_wp(struct mm_struct *mm, struct vm_area_struct *vma,
* race occurs while re-acquiring page table
* lock, and our job is done.
*/
+ delayacct_wpcopy_end();
return 0;
}

@@ -5310,6 +5315,8 @@ static vm_fault_t hugetlb_wp(struct mm_struct *mm, struct vm_area_struct *vma,
put_page(old_page);

spin_lock(ptl); /* Caller expects lock to be held */
+
+ delayacct_wpcopy_end();
return ret;
}

diff --git a/mm/memory.c b/mm/memory.c
index a82bf21be5e3..aad64c51c175 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3008,6 +3008,8 @@ static vm_fault_t wp_page_copy(struct vm_fault *vmf)
int page_copied = 0;
struct mmu_notifier_range range;

+ delayacct_wpcopy_start();
+
if (unlikely(anon_vma_prepare(vma)))
goto oom;

@@ -3032,6 +3034,8 @@ static vm_fault_t wp_page_copy(struct vm_fault *vmf)
put_page(new_page);
if (old_page)
put_page(old_page);
+
+ delayacct_wpcopy_end();
return 0;
}
}
@@ -3138,12 +3142,16 @@ static vm_fault_t wp_page_copy(struct vm_fault *vmf)
free_swap_cache(old_page);
put_page(old_page);
}
+
+ delayacct_wpcopy_end();
return page_copied && !unshare ? VM_FAULT_WRITE : 0;
oom_free_new:
put_page(new_page);
oom:
if (old_page)
put_page(old_page);
+
+ delayacct_wpcopy_end();
return VM_FAULT_OOM;
}

diff --git a/tools/accounting/getdelays.c b/tools/accounting/getdelays.c
index 11e86739456d..e83e6e47a21e 100644
--- a/tools/accounting/getdelays.c
+++ b/tools/accounting/getdelays.c
@@ -207,6 +207,8 @@ static void print_delayacct(struct taskstats *t)
"THRASHING%12s%15s%15s\n"
" %15llu%15llu%15llums\n"
"COMPACT %12s%15s%15s\n"
+ " %15llu%15llu%15llums\n"
+ "WPCOPY %12s%15s%15s\n"
" %15llu%15llu%15llums\n",
"count", "real total", "virtual total",
"delay total", "delay average",
@@ -234,7 +236,11 @@ static void print_delayacct(struct taskstats *t)
"count", "delay total", "delay average",
(unsigned long long)t->compact_count,
(unsigned long long)t->compact_delay_total,
- average_ms(t->compact_delay_total, t->compact_count));
+ average_ms(t->compact_delay_total, t->compact_count),
+ "count", "delay total", "delay average",
+ (unsigned long long)t->wpcopy_count,
+ (unsigned long long)t->wpcopy_delay_total,
+ average_ms(t->wpcopy_delay_total, t->wpcopy_count));
}

static void task_context_switch_counts(struct taskstats *t)
--
2.25.1