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From: chenqiwu <qiwuchen55@gmail.com>
To: Bernd Schubert <bernd.schubert@fastmail.fm>
Cc: miklos@szeredi.hu, linux-fsdevel@vger.kernel.org,
	chenqiwu <chenqiwu@xiaomi.com>,
	Matthew Wilcox <willy@infradead.org>
Subject: Re: [PATCH] fuse: fix inode rwsem regression
Date: Sun, 2 Feb 2020 10:08:17 +0800
Message-ID: <20200202020817.GA14887@cqw-OptiPlex-7050> (raw)
In-Reply-To: <668fc86f-4214-f315-9b41-40368ba91022@fastmail.fm>

On Sun, Feb 02, 2020 at 12:09:50AM +0100, Bernd Schubert wrote:
> 
> 
> On 2/1/20 6:49 AM, qiwuchen55@gmail.com wrote:
> > From: chenqiwu <chenqiwu@xiaomi.com>
> > 
> > Apparently our current rwsem code doesn't like doing the trylock, then
> > lock for real scheme.  So change our direct write method to just do the
> > trylock for the RWF_NOWAIT case.
> > This seems to fix AIM7 regression in some scalable filesystems upto ~25%
> > in some cases. Claimed in commit 942491c9e6d6 ("xfs: fix AIM7 regression")
> > 
> > Signed-off-by: chenqiwu <chenqiwu@xiaomi.com>
> > ---
> >  fs/fuse/file.c | 8 +++++++-
> >  1 file changed, 7 insertions(+), 1 deletion(-)
> > 
> > diff --git a/fs/fuse/file.c b/fs/fuse/file.c
> > index ce71538..ac16994 100644
> > --- a/fs/fuse/file.c
> > +++ b/fs/fuse/file.c
> > @@ -1529,7 +1529,13 @@ static ssize_t fuse_direct_write_iter(struct kiocb *iocb, struct iov_iter *from)
> >  	ssize_t res;
> >  
> >  	/* Don't allow parallel writes to the same file */
> > -	inode_lock(inode);
> > +	if (iocb->ki_flags & IOCB_NOWAIT) {
> > +		if (!inode_trylock(inode))
> > +			return -EAGAIN;
> > +	} else {
> > +		inode_lock(inode);
> > +	}
> > +
> >  	res = generic_write_checks(iocb, from);
> >  	if (res > 0) {
> >  		if (!is_sync_kiocb(iocb) && iocb->ki_flags & IOCB_DIRECT) {
> > 
> 
> 
> I would actually like to ask if we can do something about this lock
> altogether. Replace it with a range lock?  This very lock badly hurts
> fuse shared file performance and maybe I miss something, but it should
> be needed only for writes/reads going into the same file?
>
I think replacing the internal inode rwsem with a range lock maybe not
a good idea, because it may cause potential block for different writes/reads
routes when this range lock is owned by someone. Using internal inode rwsem
can avoid this range racy.

  reply index

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-01  5:49 qiwuchen55
2020-02-01 15:47 ` Matthew Wilcox
2020-02-01 23:09 ` Bernd Schubert
2020-02-02  2:08   ` chenqiwu [this message]
2020-02-02 21:18     ` Bernd Schubert
2020-02-03  3:20       ` chenqiwu
2020-02-13  9:50       ` Miklos Szeredi

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