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

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Message-ID: <20210426233823.GT1904484@iweiny-DESK2.sc.intel.com>
Date:   Mon, 26 Apr 2021 16:38:23 -0700
From:   Ira Weiny <ira.weiny@...el.com>
To:     Shiyang Ruan <ruansy.fnst@...itsu.com>
Cc:     linux-kernel@...r.kernel.org, linux-xfs@...r.kernel.org,
        linux-nvdimm@...ts.01.org, linux-fsdevel@...r.kernel.org,
        darrick.wong@...cle.com, dan.j.williams@...el.com,
        willy@...radead.org, jack@...e.cz, viro@...iv.linux.org.uk,
        linux-btrfs@...r.kernel.org, david@...morbit.com, hch@....de,
        rgoldwyn@...e.de, Ritesh Harjani <riteshh@...ux.ibm.com>
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?

Ira