Re: [f2fs-dev] [PATCH v2] f2fs: replace blk_finish_plug() with blk_flush_plug()

[Jaegeuk Kim <jaegeuk@kernel.org>]

On 09/04, Chao Yu wrote:
> On 2023/8/31 15:10, Chunhai Guo wrote:
> > The commit 344150999b7f ("f2fs: fix to avoid potential deadlock") only
> > requires unplugging current->plug. Using blk_finish_plug() is unnecessary
> > as it sets current->plug as NULL and prevents wb_writeback() from using
> > plug in subsequent loops. Instead, use blk_flush_plug() as a replacement.
> > 
> > Signed-off-by: Chunhai Guo <guochunhai@vivo.com>
> > ---
> >   fs/f2fs/data.c | 3 +--
> >   fs/f2fs/node.c | 3 +--
> >   2 files changed, 2 insertions(+), 4 deletions(-)
> > 
> > diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> > index 916e317ac925..77b4a55d6d94 100644
> > --- a/fs/f2fs/data.c
> > +++ b/fs/f2fs/data.c
> > @@ -3346,8 +3346,7 @@ static int __f2fs_write_data_pages(struct address_space *mapping,
> >   		atomic_inc(&sbi->wb_sync_req[DATA]);
> >   	else if (atomic_read(&sbi->wb_sync_req[DATA])) {
> >   		/* to avoid potential deadlock */
> > -		if (current->plug)
> > -			blk_finish_plug(current->plug);
> 
> What about?
> 
> if (current->plug) {
> 	struct blk_plug *plug = current->plug;
> 
> 	blk_finish_plug(plug);
> 	blk_start_plug(plug);
> }
> 
> Jaegeuk, thoughts?

By the way, do we really need to reuse current->plug again? After checkpoint
being done, we can use the plug in __f2fs_write_data_pages. Are there some
numbers to show the benefit?

> 
> Thanks,
> 
> > +		blk_flush_plug(current->plug, false);
> >   		goto skip_write;
> >   	}
> > diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c
> > index ee2e1dd64f25..c4b5717a8c1a 100644
> > --- a/fs/f2fs/node.c
> > +++ b/fs/f2fs/node.c
> > @@ -2126,8 +2126,7 @@ static int f2fs_write_node_pages(struct address_space *mapping,
> >   		atomic_inc(&sbi->wb_sync_req[NODE]);
> >   	else if (atomic_read(&sbi->wb_sync_req[NODE])) {
> >   		/* to avoid potential deadlock */
> > -		if (current->plug)
> > -			blk_finish_plug(current->plug);
> > +		blk_flush_plug(current->plug, false);
> >   		goto skip_write;
> >   	}


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