Hi Jaegeuk,
> -----Original Message-----
> From: Jaegeuk Kim [mailto:jaeg...@kernel.org]
> Sent: Thursday, July 31, 2014 2:45 PM
> To: Chao Yu
> Cc: 'Changman Lee'; linux-fsde...@vger.kernel.org;
> linux-kernel@vger.kernel.org;
> linux-f2fs-de...@lists.sourceforge.net
> Subject: Re: [f2fs-dev] [PATCH] f2fs: reduce competition among node page
> writes
>
> On Thu, Jul 31, 2014 at 01:31:46PM +0800, Chao Yu wrote:
> > Hi Changman,
> >
> > > -----Original Message-----
> > > From: Changman Lee [mailto:cm224....@samsung.com]
> > > Sent: Thursday, July 31, 2014 10:07 AM
> > > To: Chao Yu
> > > Cc: 'Jaegeuk Kim'; linux-fsde...@vger.kernel.org;
> > > linux-kernel@vger.kernel.org;
> > > linux-f2fs-de...@lists.sourceforge.net
> > > 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...@samsung.com]
> > > > > Sent: Thursday, July 03, 2014 6:59 PM
> > > > > To: Jaegeuk Kim; Changman Lee
> > > > > Cc: linux-fsde...@vger.kernel.org; linux-kernel@vger.kernel.org;
> > > > > linux-f2fs-de...@lists.sourceforge.net
> > > > > 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?
>
> Oh, I forgot to send an email for this.
> At that time, when I looked at a glance, I thought that it was not clear why
> this should be merged.
>
> But, when I contemplate again, it seems that several fsync threads could
> produce
> multiple node writers, resulting in some mutex contention.
> Just for sure, can you verify that?
Yes, node sync in cp could encounter competition of the same op in
fsync/flush/gc
thread. Here we use rwlock to increase concurrent of these thread hence we could
gain better performance of checkpoint.
Thanks,
Yu
>
> Nevertheless, I think there would be no problem to merge this patch now.
> Merged.
>
> >
> > >
> > > >
> > > > 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.
>
> Good. :)
>
> >
> > 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...@samsung.com>
> > > > > ---
> > > > > 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
> > > > >
> > > > >
> > > > >
> > > > > ------------------------------------------------------------------------------
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> > > > > _______________________________________________
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