Re: [PATCH v3 1/3] fsdax: Factor helpers to simplify dax fault code

From: Ira Weiny <ira.weiny@intel.com>
To: "ruansy.fnst@fujitsu.com" <ruansy.fnst@fujitsu.com>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"linux-xfs@vger.kernel.org" <linux-xfs@vger.kernel.org>,
	"linux-nvdimm@lists.01.org" <linux-nvdimm@lists.01.org>,
	"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
	"darrick.wong@oracle.com" <darrick.wong@oracle.com>,
	"dan.j.williams@intel.com" <dan.j.williams@intel.com>,
	"willy@infradead.org" <willy@infradead.org>,
	"jack@suse.cz" <jack@suse.cz>,
	"viro@zeniv.linux.org.uk" <viro@zeniv.linux.org.uk>,
	"linux-btrfs@vger.kernel.org" <linux-btrfs@vger.kernel.org>,
	"david@fromorbit.com" <david@fromorbit.com>,
	"hch@lst.de" <hch@lst.de>, "rgoldwyn@suse.de" <rgoldwyn@suse.de>,
	Ritesh Harjani <riteshh@linux.ibm.com>
Subject: Re: [PATCH v3 1/3] fsdax: Factor helpers to simplify dax fault code
Date: Tue, 27 Apr 2021 09:34:26 -0700	[thread overview]
Message-ID: <20210427163425.GW1904484@iweiny-DESK2.sc.intel.com> (raw)
In-Reply-To: <OSBPR01MB292025E6E88319A902C980FEF4419@OSBPR01MB2920.jpnprd01.prod.outlook.com>

On Tue, Apr 27, 2021 at 02:44:33AM +0000, ruansy.fnst@fujitsu.com wrote:
> > -----Original Message-----
> > From: Ira Weiny <ira.weiny@intel.com>
> > Sent: Tuesday, April 27, 2021 7:38 AM
> > Subject: Re: [PATCH v3 1/3] fsdax: Factor helpers to simplify dax fault code
> > 
> > On Thu, Apr 22, 2021 at 09:44:59PM +0800, Shiyang Ruan wrote:
> > > The dax page fault code is too long and a bit difficult to read. And
> > > it is hard to understand when we trying to add new features. Some of
> > > the PTE/PMD codes have similar logic. So, factor them as helper
> > > functions to simplify the code.
> > >
> > > Signed-off-by: Shiyang Ruan <ruansy.fnst@fujitsu.com>
> > > Reviewed-by: Christoph Hellwig <hch@lst.de>
> > > Reviewed-by: Ritesh Harjani <riteshh@linux.ibm.com>
> > > ---
> > >  fs/dax.c | 153
> > > ++++++++++++++++++++++++++++++-------------------------
> > >  1 file changed, 84 insertions(+), 69 deletions(-)
> > >
> > > diff --git a/fs/dax.c b/fs/dax.c
> > > index b3d27fdc6775..f843fb8fbbf1 100644
> > > --- a/fs/dax.c
> > > +++ b/fs/dax.c
> > 
> > [snip]
> > 
> > > @@ -1355,19 +1379,8 @@ static vm_fault_t dax_iomap_pte_fault(struct
> > vm_fault *vmf, pfn_t *pfnp,
> > >  		entry = dax_insert_entry(&xas, mapping, vmf, entry, pfn,
> > >  						 0, write && !sync);
> > >
> > > -		/*
> > > -		 * If we are doing synchronous page fault and inode needs fsync,
> > > -		 * we can insert PTE into page tables only after that happens.
> > > -		 * Skip insertion for now and return the pfn so that caller can
> > > -		 * insert it after fsync is done.
> > > -		 */
> > >  		if (sync) {
> > > -			if (WARN_ON_ONCE(!pfnp)) {
> > > -				error = -EIO;
> > > -				goto error_finish_iomap;
> > > -			}
> > > -			*pfnp = pfn;
> > > -			ret = VM_FAULT_NEEDDSYNC | major;
> > > +			ret = dax_fault_synchronous_pfnp(pfnp, pfn);
> > 
> > I commented on the previous version...  So I'll ask here too.
> > 
> > Why is it ok to drop 'major' here?
> 
> This dax_iomap_pte_fault () finally returns 'ret | major', so I think the major here is not dropped.  The origin code seems OR the return value and major twice.
> 

Thanks I missed that!
Ira