On 08/04, Chao Yu wrote:
> On 2020/8/4 9:04, Jaegeuk Kim wrote:
> > On 08/04, Chao Yu wrote:
> > > On 2020/8/4 1:28, Jaegeuk Kim wrote:
> > > > It doesn't need to wait for checkpoint being completed triggered by
> > > > end_io.
> > > >
> > > > [ 20.157753] ------------[ cut here ]------------
> > > > [ 20.158393] do not call blocking ops when !TASK_RUNNING; state=2 set
> > > > at [<0000000096354225>] prepare_to_wait+0xcd/0x430
> > > > [ 20.159858] WARNING: CPU: 1 PID: 1152 at kernel/sched/core.c:7142
> > > > __might_sleep+0x149/0x1a0
> > > > ...
> > > > [ 20.176110] __submit_merged_write_cond+0x191/0x310
> > > > [ 20.176739] f2fs_submit_merged_write+0x18/0x20
> > > > [ 20.177323] f2fs_wait_on_all_pages+0x269/0x2d0
> > > > [ 20.177899] ? block_operations+0x980/0x980
> > > > [ 20.178441] ? __kasan_check_read+0x11/0x20
> > > > [ 20.178975] ? finish_wait+0x260/0x260
> > > > [ 20.179488] ? percpu_counter_set+0x147/0x230
> > > > [ 20.180049] do_checkpoint+0x1757/0x2a50
> > > > [ 20.180558] f2fs_write_checkpoint+0x840/0xaf0
> > > > [ 20.181126] f2fs_sync_fs+0x287/0x4a0
> > > >
> > > > Reported-by: Eric Biggers <ebigg...@kernel.org>
> > > > Signed-off-by: Jaegeuk Kim <jaeg...@kernel.org>
> > > > ---
> > > > fs/f2fs/checkpoint.c | 6 +-----
> > > > fs/f2fs/data.c | 4 ----
> > > > fs/f2fs/f2fs.h | 1 -
> > > > fs/f2fs/super.c | 1 -
> > > > 4 files changed, 1 insertion(+), 11 deletions(-)
> > > >
> > > > diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
> > > > index 99c8061da55b9..2bdddc725e677 100644
> > > > --- a/fs/f2fs/checkpoint.c
> > > > +++ b/fs/f2fs/checkpoint.c
> > > > @@ -1255,11 +1255,7 @@ static void unblock_operations(struct
> > > > f2fs_sb_info *sbi)
> > > > void f2fs_wait_on_all_pages(struct f2fs_sb_info *sbi, int type)
> > > > {
> > > > - DEFINE_WAIT(wait);
> > > > -
> > > > for (;;) {
> > > > - prepare_to_wait(&sbi->cp_wait, &wait,
> > > > TASK_UNINTERRUPTIBLE);
> > >
> > > Wouldn't that case high cpu usage before io end?
> >
> > This is a critical path to wait for IO completion in checkpoint, which
> > would be
> > better to wait for it to avoid long latency to continue filesystem
> > operations.
>
> Yup, in previous implementation, last end_io wakes up checkpoint() waiter, we
> didn't waste any time there.
>
> > Moreover, I expect io_schedule_timeout() can mitigate such the CPU overhead
> > and
> > actually we don't need to make there-in context switches as well.
>
> Then io_schedule_timeout() in this loop may give CPU time slice to other
> thread
> until scheduler reselect checkpoint(), that would cause longer latency?
Hmm, how about this then?
>From 4956afa1cedc019cabf6e8bff7bc48d3bcf7a3f5 Mon Sep 17 00:00:00 2001
From: Jaegeuk Kim <jaeg...@kernel.org>
Date: Mon, 3 Aug 2020 19:37:12 -0700
Subject: [PATCH] f2fs: prepare a waiter before entering io_schedule
This is to avoid sleep() in the waiter thread.
[ 20.157753] ------------[ cut here ]------------
[ 20.158393] do not call blocking ops when !TASK_RUNNING; state=2 set at
[<0000000096354225>] prepare_to_wait+0xcd/0x430
[ 20.159858] WARNING: CPU: 1 PID: 1152 at kernel/sched/core.c:7142
__might_sleep+0x149/0x1a0
...
[ 20.176110] __submit_merged_write_cond+0x191/0x310
[ 20.176739] f2fs_submit_merged_write+0x18/0x20
[ 20.177323] f2fs_wait_on_all_pages+0x269/0x2d0
[ 20.177899] ? block_operations+0x980/0x980
[ 20.178441] ? __kasan_check_read+0x11/0x20
[ 20.178975] ? finish_wait+0x260/0x260
[ 20.179488] ? percpu_counter_set+0x147/0x230
[ 20.180049] do_checkpoint+0x1757/0x2a50
[ 20.180558] f2fs_write_checkpoint+0x840/0xaf0
[ 20.181126] f2fs_sync_fs+0x287/0x4a0
Reported-by: Eric Biggers <ebigg...@kernel.org>
Signed-off-by: Jaegeuk Kim <jaeg...@kernel.org>
---
fs/f2fs/checkpoint.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
index 99c8061da55b9..ff807e14c8911 100644
--- a/fs/f2fs/checkpoint.c
+++ b/fs/f2fs/checkpoint.c
@@ -1258,8 +1258,6 @@ void f2fs_wait_on_all_pages(struct f2fs_sb_info *sbi, int
type)
DEFINE_WAIT(wait);
for (;;) {
- prepare_to_wait(&sbi->cp_wait, &wait, TASK_UNINTERRUPTIBLE);
-
if (!get_pages(sbi, type))
break;
@@ -1271,6 +1269,8 @@ void f2fs_wait_on_all_pages(struct f2fs_sb_info *sbi, int
type)
FS_CP_META_IO);
else if (type == F2FS_WB_CP_DATA)
f2fs_submit_merged_write(sbi, DATA);
+
+ prepare_to_wait(&sbi->cp_wait, &wait, TASK_UNINTERRUPTIBLE);
io_schedule_timeout(DEFAULT_IO_TIMEOUT);
}
finish_wait(&sbi->cp_wait, &wait);
--
2.28.0.163.g6104cc2f0b6-goog
