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Date: Tue, 08 Oct 2013 11:30:14 +0000 (GMT)
From: Yuan Zhong <yuan.mark.zhong@...sung.com>
To: Gu Zheng <guz.fnst@...fujitsu.com>
Cc: Jaegeuk Kim <jaegeuk.kim@...sung.com>,
"linux-f2fs-devel@...ts.sourceforge.net"
<linux-f2fs-devel@...ts.sourceforge.net>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
shu tan <shu.tan@...sung.com>
Subject: Re: [f2fs-dev] [PATCH v2] f2fs: avoid congestion_wait when
do_checkpoint for better performance
Hi Gu,
> Hi Yuan,
> On 10/08/2013 04:30 PM, Yuan Zhong wrote:
> > Previously, do_checkpoint() will call congestion_wait() for waiting the pages (previous submitted node/meta/data pages) to be written back.
> > Because congestion_wait() will set a regular period (e.g. HZ / 50 ) for waiting.
> > For this reason, there is a situation that after the pages have been written back,
> > but the checkpoint thread still wait for congestion_wait to exit.
> How do you confirm this issue?
I traced the execution path.
In f2fs_end_io_write, dec_page_count(p->sbi, F2FS_WRITEBACK) will be called.
And I found that, when pages of F2FS_WRITEBACK has been zero, but
checkpoint thread still congestion_wait for pages of F2FS_WRITEBACK to be zero.
So, I think this point could be improved.
And I wrote a simple test case and tested on Micro-SD card, the steps as following:
(a) create a fixed-size file (4KB)
(b) go on to sync the file
(c) go back to step #a (fixed numbers of cycling:1024)
The results indicated that the execution time is reduced greatly by using this patch.
> I suspect that the block-core does not have a wake-up mechanism
> when the back device is uncongested.
Yes, you are right.
So I wake up the checkpoint thread by myself, when pages of F2FS_WRITEBACK to be zero.
In f2fs_end_io_write, f2fs_writeback_wait is called.
you cloud find this code in my patch.
> > This is a problem here, especially, when sync a large number of small files or dirs.
> > In order to avoid this, a wait_list is introduced,
> > the checkpoint thread will be dropped into the wait_list if the pages have not been written back,
> > and will be waked up by contrast.
> Please pay some attention to the mail form, this mail is out of format in my mail client.
> Regards,
> Gu
Regards,
Yuan
> >
> > Signed-off-by: Yuan Zhong <yuan.mark.zhong@...sung.com>
> > ---
> > fs/f2fs/checkpoint.c | 3 +--
> > fs/f2fs/f2fs.h | 19 +++++++++++++++++++
> > fs/f2fs/segment.c | 1 +
> > fs/f2fs/super.c | 1 +
> > 4 files changed, 22 insertions(+), 2 deletions(-)
> >
> > diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
> > index ca39442..5d69ae0 100644
> > --- a/fs/f2fs/checkpoint.c
> > +++ b/fs/f2fs/checkpoint.c
> > @@ -758,8 +758,7 @@ static void do_checkpoint(struct f2fs_sb_info *sbi, bool is_umount)
> > f2fs_put_page(cp_page, 1);
> >
> > /* wait for previous submitted node/meta pages writeback */
> > - while (get_pages(sbi, F2FS_WRITEBACK))
> > - congestion_wait(BLK_RW_ASYNC, HZ / 50);
> > + f2fs_writeback_wait(sbi);
> >
> > filemap_fdatawait_range(sbi->node_inode->i_mapping, 0, LONG_MAX);
> > filemap_fdatawait_range(sbi->meta_inode->i_mapping, 0, LONG_MAX);
> > diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> > index 7fd99d8..4b0d70e 100644
> > --- a/fs/f2fs/f2fs.h
> > +++ b/fs/f2fs/f2fs.h
> > @@ -18,6 +18,8 @@
> > #include <linux/crc32.h>
> > #include <linux/magic.h>
> > #include <linux/kobject.h>
> > +#include <linux/wait.h>
> > +#include <linux/sched.h>
> >
> > /*
> > * For mount options
> > @@ -368,6 +370,7 @@ struct f2fs_sb_info {
> > struct mutex fs_lock[NR_GLOBAL_LOCKS]; /* blocking FS operations */
> > struct mutex node_write; /* locking node writes */
> > struct mutex writepages; /* mutex for writepages() */
> > + wait_queue_head_t writeback_wqh; /* wait_queue for writeback */
> > unsigned char next_lock_num; /* round-robin global locks */
> > int por_doing; /* recovery is doing or not */
> > int on_build_free_nids; /* build_free_nids is doing */
> > @@ -961,6 +964,22 @@ static inline int f2fs_readonly(struct super_block *sb)
> > return sb->s_flags & MS_RDONLY;
> > }
> >
> > +static inline void f2fs_writeback_wait(struct f2fs_sb_info *sbi)
> > +{
> > + DEFINE_WAIT(wait);
> > +
> > + prepare_to_wait(&sbi->writeback_wqh, &wait, TASK_UNINTERRUPTIBLE);
> > + if (get_pages(sbi, F2FS_WRITEBACK))
> > + io_schedule();
> > + finish_wait(&sbi->writeback_wqh, &wait);
> > +}
> > +
> > +static inline void f2fs_writeback_wake(struct f2fs_sb_info *sbi)
> > +{
> > + if (!get_pages(sbi, F2FS_WRITEBACK))
> > + wake_up_all(&sbi->writeback_wqh);
> > +}
> > +
> > /*
> > * file.c
> > */
> > diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> > index bd79bbe..0708aa9 100644
> > --- a/fs/f2fs/segment.c
> > +++ b/fs/f2fs/segment.c
> > @@ -597,6 +597,7 @@ static void f2fs_end_io_write(struct bio *bio, int err)
> >
> > if (p->is_sync)
> > complete(p->wait);
> > + f2fs_writeback_wake(p->sbi);
> > kfree(p);
> > bio_put(bio);
> > }
> > diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
> > index 094ccc6..3ac6d85 100644
> > --- a/fs/f2fs/super.c
> > +++ b/fs/f2fs/super.c
> > @@ -835,6 +835,7 @@ static int f2fs_fill_super(struct super_block *sb, void *data, int silent)
> > mutex_init(&sbi->gc_mutex);
> > mutex_init(&sbi->writepages);
> > mutex_init(&sbi->cp_mutex);
> > + init_waitqueue_head(&sbi->writeback_wqh);
> > for (i = 0; i < NR_GLOBAL_LOCKS; i++)
> > mutex_init(&sbi->fs_lock[i]);
> > mutex_init(&sbi->node_write);
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