linux-kernel - RE: [PATCH v3 1/3] fsdax: Factor helpers to simplify dax fault code

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Message-ID: <OSBPR01MB292025E6E88319A902C980FEF4419@OSBPR01MB2920.jpnprd01.prod.outlook.com>
Date:   Tue, 27 Apr 2021 02:44:33 +0000
From:   "ruansy.fnst@...itsu.com" <ruansy.fnst@...itsu.com>
To:     Ira Weiny <ira.weiny@...el.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-xfs@...r.kernel.org" <linux-xfs@...r.kernel.org>,
        "linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "darrick.wong@...cle.com" <darrick.wong@...cle.com>,
        "dan.j.williams@...el.com" <dan.j.williams@...el.com>,
        "willy@...radead.org" <willy@...radead.org>,
        "jack@...e.cz" <jack@...e.cz>,
        "viro@...iv.linux.org.uk" <viro@...iv.linux.org.uk>,
        "linux-btrfs@...r.kernel.org" <linux-btrfs@...r.kernel.org>,
        "david@...morbit.com" <david@...morbit.com>,
        "hch@....de" <hch@....de>, "rgoldwyn@...e.de" <rgoldwyn@...e.de>,
        Ritesh Harjani <riteshh@...ux.ibm.com>
Subject: RE: [PATCH v3 1/3] fsdax: Factor helpers to simplify dax fault code

> -----Original Message-----
> From: Ira Weiny <ira.weiny@...el.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@...itsu.com>
> > Reviewed-by: Christoph Hellwig <hch@....de>
> > Reviewed-by: Ritesh Harjani <riteshh@...ux.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,
Ruan Shiyang.

> 
> Ira