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From: "Darrick J. Wong" <djwong@kernel.org>
To: Shiyang Ruan <ruansy.fnst@fujitsu.com>
Cc: linux-kernel@vger.kernel.org, linux-xfs@vger.kernel.org,
	nvdimm@lists.linux.dev, linux-mm@kvack.org,
	linux-fsdevel@vger.kernel.org, dan.j.williams@intel.com,
	david@fromorbit.com, hch@infradead.org, jane.chu@oracle.com
Subject: Re: [PATCH v7 8/8] fsdax: add exception for reflinked files
Date: Thu, 14 Oct 2021 12:24:50 -0700	[thread overview]
Message-ID: <20211014192450.GJ24307@magnolia> (raw)
In-Reply-To: <20210924130959.2695749-9-ruansy.fnst@fujitsu.com>

On Fri, Sep 24, 2021 at 09:09:59PM +0800, Shiyang Ruan wrote:
> For reflinked files, one dax page may be associated more than once with
> different fime mapping and index.  It will report warning.  Now, since
> we have introduced dax-RMAP for this case and also have to keep its
> functionality for other filesystems who are not support rmap, I add this
> exception here.
> 
> Signed-off-by: Shiyang Ruan <ruansy.fnst@fujitsu.com>
> ---
>  fs/dax.c | 14 ++++++++------
>  1 file changed, 8 insertions(+), 6 deletions(-)
> 
> diff --git a/fs/dax.c b/fs/dax.c
> index 2536c105ec7f..1a57211b1bc9 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -352,9 +352,10 @@ static void dax_associate_entry(void *entry, struct address_space *mapping,
>  	for_each_mapped_pfn(entry, pfn) {
>  		struct page *page = pfn_to_page(pfn);
>  
> -		WARN_ON_ONCE(page->mapping);
> -		page->mapping = mapping;
> -		page->index = index + i++;
> +		if (!page->mapping) {
> +			page->mapping = mapping;
> +			page->index = index + i++;

It feels a little dangerous to have page->mapping for shared storage
point to an actual address_space when there are really multiple
potential address_spaces out there.  If the mm or dax folks are ok with
doing this this way then I'll live with it, but it seems like you'd want
to leave /some/ kind of marker once you know that the page has multiple
owners and therefore regular mm rmap via page->mapping won't work.

--D

> +		}
>  	}
>  }
>  
> @@ -370,9 +371,10 @@ static void dax_disassociate_entry(void *entry, struct address_space *mapping,
>  		struct page *page = pfn_to_page(pfn);
>  
>  		WARN_ON_ONCE(trunc && page_ref_count(page) > 1);
> -		WARN_ON_ONCE(page->mapping && page->mapping != mapping);
> -		page->mapping = NULL;
> -		page->index = 0;
> +		if (page->mapping == mapping) {
> +			page->mapping = NULL;
> +			page->index = 0;
> +		}
>  	}
>  }
>  
> -- 
> 2.33.0
> 
> 
> 

  reply	other threads:[~2021-10-14 19:24 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-24 13:09 [PATCH v7 0/8] [PATCH v7 0/8] fsdax: introduce fs query to support reflink Shiyang Ruan
2021-09-24 13:09 ` [PATCH v7 1/8] dax: Use rwsem for dax_{read,write}_lock() Shiyang Ruan
2021-10-14 17:48   ` Darrick J. Wong
2021-10-20  5:19     ` Shiyang Ruan
2021-10-15  6:30   ` Christoph Hellwig
2021-09-24 13:09 ` [PATCH v7 2/8] dax: Introduce holder for dax_device Shiyang Ruan
2021-10-14 18:00   ` Darrick J. Wong
2021-10-20  6:58     ` Shiyang Ruan
2021-09-24 13:09 ` [PATCH v7 3/8] mm: factor helpers for memory_failure_dev_pagemap Shiyang Ruan
2021-10-14 18:02   ` Darrick J. Wong
2021-10-15  6:33   ` Christoph Hellwig
2021-09-24 13:09 ` [PATCH v7 4/8] pagemap,pmem: Introduce ->memory_failure() Shiyang Ruan
2021-10-14 18:05   ` Darrick J. Wong
2021-10-20  5:25     ` Shiyang Ruan
2021-10-15  6:36   ` Christoph Hellwig
2021-09-24 13:09 ` [PATCH v7 5/8] fsdax: Introduce dax_lock_mapping_entry() Shiyang Ruan
2021-10-14 18:17   ` Darrick J. Wong
2021-09-24 13:09 ` [PATCH v7 6/8] mm: Introduce mf_dax_kill_procs() for fsdax case Shiyang Ruan
2021-10-14 19:32   ` Darrick J. Wong
2021-10-20  5:47     ` Shiyang Ruan
2021-09-24 13:09 ` [PATCH v7 7/8] xfs: Implement ->notify_failure() for XFS Shiyang Ruan
2021-10-14 19:21   ` Darrick J. Wong
2021-10-15  6:41   ` Christoph Hellwig
2021-09-24 13:09 ` [PATCH v7 8/8] fsdax: add exception for reflinked files Shiyang Ruan
2021-10-14 19:24   ` Darrick J. Wong [this message]
2021-10-15  6:38     ` Christoph Hellwig

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