RE: [f2fs-dev] [PATCH] f2fs: reduce competition among node page writes

[Chao Yu]

Hi Changman,

> -----Original Message-----
> From: Changman Lee [mailto:cm224.lee@xxxxxxxxxxx]
> Sent: Thursday, July 31, 2014 10:07 AM
> To: Chao Yu
> Cc: 'Jaegeuk Kim'; linux-fsdevel@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
> linux-f2fs-devel@xxxxxxxxxxxxxxxxxxxxx
> Subject: Re: [f2fs-dev] [PATCH] f2fs: reduce competition among node page writes
> 
> Hi Chao,
> 
> On Wed, Jul 30, 2014 at 09:07:49PM +0800, Chao Yu wrote:
> > Hi Jaegeuk Changman,
> >
> > > -----Original Message-----
> > > From: Chao Yu [mailto:chao2.yu@xxxxxxxxxxx]
> > > Sent: Thursday, July 03, 2014 6:59 PM
> > > To: Jaegeuk Kim; Changman Lee
> > > Cc: linux-fsdevel@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
> > > linux-f2fs-devel@xxxxxxxxxxxxxxxxxxxxx
> > > Subject: [f2fs-dev] [PATCH] f2fs: reduce competition among node page writes
> > >
> > > We do not need to block on ->node_write among different node page writers e.g.
> > > fsync/flush, unless we have a node page writer from write_checkpoint.
> > > So it's better use rw_semaphore instead of mutex type for ->node_write to
> > > promote performance.
> >
> > If you could have time to help explaining the problem of this patch, I will be
> > appreciated for that.
> 
> I have no clue. Except checkpoint, I don't know why need to block to
> write node page.
> Do you have any problem when you test with this patch?

I don't have.
I send this patch about one month ago, but got no respond.
So I want to ask if any problem in this patch or forget to look at this patch?

To Jaegeuk:
Any idea about this patch?

> 
> >
> > Another question is what is ->writepages in sbi used for? I'm not quite clear.
> >
> 
> I remember it is for writing data pages per thread as much as possible.
> When multi-threads write some files simultaneously, multi-threads contended with
> each other to allocate a block. So block allocation was interleaved
> across threads. It makes fragmentation of file.

Thank you for the explanation! :)
I think what you say is reasonable.

Previously I tested without this lock, although I found that the blocks written
_almost_ were continuous in each '->writepages()'. Still I think we can gain more
from readahead continuous block when using this lock, rather than remove it for
promoting concurrent of writers.

Thanks,
Yu

> 
> Thanks,
> 
> > Thanks,
> >
> > >
> > > Signed-off-by: Chao Yu <chao2.yu@xxxxxxxxxxx>
> > > ---
> > >  fs/f2fs/checkpoint.c |    6 +++---
> > >  fs/f2fs/f2fs.h       |    2 +-
> > >  fs/f2fs/node.c       |    4 ++--
> > >  fs/f2fs/super.c      |    2 +-
> > >  4 files changed, 7 insertions(+), 7 deletions(-)
> > >
> > > diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
> > > index 0b4710c..eec406b 100644
> > > --- a/fs/f2fs/checkpoint.c
> > > +++ b/fs/f2fs/checkpoint.c
> > > @@ -714,10 +714,10 @@ retry_flush_dents:
> > >  	 * until finishing nat/sit flush.
> > >  	 */
> > >  retry_flush_nodes:
> > > -	mutex_lock(&sbi->node_write);
> > > +	down_write(&sbi->node_write);
> > >
> > >  	if (get_pages(sbi, F2FS_DIRTY_NODES)) {
> > > -		mutex_unlock(&sbi->node_write);
> > > +		up_write(&sbi->node_write);
> > >  		sync_node_pages(sbi, 0, &wbc);
> > >  		goto retry_flush_nodes;
> > >  	}
> > > @@ -726,7 +726,7 @@ retry_flush_nodes:
> > >
> > >  static void unblock_operations(struct f2fs_sb_info *sbi)
> > >  {
> > > -	mutex_unlock(&sbi->node_write);
> > > +	up_write(&sbi->node_write);
> > >  	f2fs_unlock_all(sbi);
> > >  }
> > >
> > > diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> > > index ae3b4ac..ca30b5a 100644
> > > --- a/fs/f2fs/f2fs.h
> > > +++ b/fs/f2fs/f2fs.h
> > > @@ -444,7 +444,7 @@ struct f2fs_sb_info {
> > >  	struct inode *meta_inode;		/* cache meta blocks */
> > >  	struct mutex cp_mutex;			/* checkpoint procedure lock */
> > >  	struct rw_semaphore cp_rwsem;		/* blocking FS operations */
> > > -	struct mutex node_write;		/* locking node writes */
> > > +	struct rw_semaphore node_write;		/* locking node writes */
> > >  	struct mutex writepages;		/* mutex for writepages() */
> > >  	bool por_doing;				/* recovery is doing or not */
> > >  	wait_queue_head_t cp_wait;
> > > diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c
> > > index a90f51d..7b5b5de 100644
> > > --- a/fs/f2fs/node.c
> > > +++ b/fs/f2fs/node.c
> > > @@ -1231,12 +1231,12 @@ static int f2fs_write_node_page(struct page *page,
> > >  	if (wbc->for_reclaim)
> > >  		goto redirty_out;
> > >
> > > -	mutex_lock(&sbi->node_write);
> > > +	down_read(&sbi->node_write);
> > >  	set_page_writeback(page);
> > >  	write_node_page(sbi, page, &fio, nid, ni.blk_addr, &new_addr);
> > >  	set_node_addr(sbi, &ni, new_addr, is_fsync_dnode(page));
> > >  	dec_page_count(sbi, F2FS_DIRTY_NODES);
> > > -	mutex_unlock(&sbi->node_write);
> > > +	up_read(&sbi->node_write);
> > >  	unlock_page(page);
> > >  	return 0;
> > >
> > > diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
> > > index 8f96d93..bed9413 100644
> > > --- a/fs/f2fs/super.c
> > > +++ b/fs/f2fs/super.c
> > > @@ -947,7 +947,7 @@ 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);
> > > -	mutex_init(&sbi->node_write);
> > > +	init_rwsem(&sbi->node_write);
> > >  	sbi->por_doing = false;
> > >  	spin_lock_init(&sbi->stat_lock);
> > >
> > > --
> > > 1.7.9.5
> > >
> > >
> > >
> > > ------------------------------------------------------------------------------
> > > Open source business process management suite built on Java and Eclipse
> > > Turn processes into business applications with Bonita BPM Community Edition
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> > > _______________________________________________
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