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From: David Sterba <dsterba@suse.cz>
To: Shiyang Ruan <ruansy.fnst@cn.fujitsu.com>
Cc: jack@suse.cz, darrick.wong@oracle.com, linux-nvdimm@lists.01.org,
	david@fromorbit.com, linux-kernel@vger.kernel.org,
	linux-xfs@vger.kernel.org, ocfs2-devel@oss.oracle.com,
	viro@zeniv.linux.org.uk, Goldwyn Rodrigues <rgoldwyn@suse.com>,
	linux-fsdevel@vger.kernel.org, dan.j.williams@intel.com,
	linux-btrfs@vger.kernel.org
Subject: Re: [Ocfs2-devel] [PATCH 4/7] fsdax: Replace mmap entry in case of CoW
Date: Tue, 16 Feb 2021 14:11:54 +0100	[thread overview]
Message-ID: <20210216131154.GN1993@twin.jikos.cz> (raw)
In-Reply-To: <20210207170924.2933035-5-ruansy.fnst@cn.fujitsu.com>

On Mon, Feb 08, 2021 at 01:09:21AM +0800, Shiyang Ruan wrote:
> We replace the existing entry to the newly allocated one
> in case of CoW. Also, we mark the entry as PAGECACHE_TAG_TOWRITE
> so writeback marks this entry as writeprotected. This
> helps us snapshots so new write pagefaults after snapshots
> trigger a CoW.
> 
> Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
> Signed-off-by: Shiyang Ruan <ruansy.fnst@cn.fujitsu.com>
> ---
>  fs/dax.c | 31 +++++++++++++++++++++++--------
>  1 file changed, 23 insertions(+), 8 deletions(-)
> 
> diff --git a/fs/dax.c b/fs/dax.c
> index b2195cbdf2dc..29698a3d2e37 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -722,6 +722,9 @@ static int copy_cow_page_dax(struct block_device *bdev, struct dax_device *dax_d
>  	return 0;
>  }
>  
> +#define DAX_IF_DIRTY		(1ULL << 0)
> +#define DAX_IF_COW		(1ULL << 1)

The constants are ULL, but I see other flags only 'unsigned long'

> +
>  /*
>   * By this point grab_mapping_entry() has ensured that we have a locked entry
>   * of the appropriate size so we don't have to worry about downgrading PMDs to
> @@ -731,14 +734,16 @@ static int copy_cow_page_dax(struct block_device *bdev, struct dax_device *dax_d
>   */
>  static void *dax_insert_entry(struct xa_state *xas,
>  		struct address_space *mapping, struct vm_fault *vmf,
> -		void *entry, pfn_t pfn, unsigned long flags, bool dirty)
> +		void *entry, pfn_t pfn, unsigned long flags, bool insert_flags)

insert_flags is bool

>  {
>  	void *new_entry = dax_make_entry(pfn, flags);
> +	bool dirty = insert_flags & DAX_IF_DIRTY;

"insert_flags & DAX_IF_DIRTY" is "bool & ULL", this can't be right

> +	bool cow = insert_flags & DAX_IF_COW;

Same

>  
>  	if (dirty)
>  		__mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
>  
> -	if (dax_is_zero_entry(entry) && !(flags & DAX_ZERO_PAGE)) {
> +	if (cow || (dax_is_zero_entry(entry) && !(flags & DAX_ZERO_PAGE))) {
>  		unsigned long index = xas->xa_index;
>  		/* we are replacing a zero page with block mapping */
>  		if (dax_is_pmd_entry(entry))
> @@ -750,7 +755,7 @@ static void *dax_insert_entry(struct xa_state *xas,
>  
>  	xas_reset(xas);
>  	xas_lock_irq(xas);
> -	if (dax_is_zero_entry(entry) || dax_is_empty_entry(entry)) {
> +	if (cow || dax_is_zero_entry(entry) || dax_is_empty_entry(entry)) {
>  		void *old;
>  
>  		dax_disassociate_entry(entry, mapping, false);
> @@ -774,6 +779,9 @@ static void *dax_insert_entry(struct xa_state *xas,
>  	if (dirty)
>  		xas_set_mark(xas, PAGECACHE_TAG_DIRTY);
>  
> +	if (cow)
> +		xas_set_mark(xas, PAGECACHE_TAG_TOWRITE);
> +
>  	xas_unlock_irq(xas);
>  	return entry;
>  }
> @@ -1319,6 +1327,7 @@ static vm_fault_t dax_iomap_pte_fault(struct vm_fault *vmf, pfn_t *pfnp,
>  	void *entry;
>  	pfn_t pfn;
>  	void *kaddr;
> +	unsigned long insert_flags = 0;
>  
>  	trace_dax_pte_fault(inode, vmf, ret);
>  	/*
> @@ -1444,8 +1453,10 @@ static vm_fault_t dax_iomap_pte_fault(struct vm_fault *vmf, pfn_t *pfnp,
>  
>  		goto finish_iomap;
>  	case IOMAP_UNWRITTEN:
> -		if (write && iomap.flags & IOMAP_F_SHARED)
> +		if (write && (iomap.flags & IOMAP_F_SHARED)) {
> +			insert_flags |= DAX_IF_COW;

Here's an example of 'unsigned long = unsigned long long', though it'll
work, it would be better to unify all the types.

>  			goto cow;
> +		}
>  		fallthrough;
>  	case IOMAP_HOLE:
>  		if (!write) {
> @@ -1555,6 +1566,7 @@ static vm_fault_t dax_iomap_pmd_fault(struct vm_fault *vmf, pfn_t *pfnp,
>  	int error;
>  	pfn_t pfn;
>  	void *kaddr;
> +	unsigned long insert_flags = 0;
>  
>  	/*
>  	 * Check whether offset isn't beyond end of file now. Caller is
> @@ -1670,14 +1682,17 @@ static vm_fault_t dax_iomap_pmd_fault(struct vm_fault *vmf, pfn_t *pfnp,
>  		result = vmf_insert_pfn_pmd(vmf, pfn, write);
>  		break;
>  	case IOMAP_UNWRITTEN:
> -		if (write && iomap.flags & IOMAP_F_SHARED)
> +		if (write && (iomap.flags & IOMAP_F_SHARED)) {
> +			insert_flags |= DAX_IF_COW;
>  			goto cow;
> +		}
>  		fallthrough;
>  	case IOMAP_HOLE:
> -		if (WARN_ON_ONCE(write))
> +		if (!write) {
> +			result = dax_pmd_load_hole(&xas, vmf, &iomap, &entry);
>  			break;
> -		result = dax_pmd_load_hole(&xas, vmf, &iomap, &entry);
> -		break;
> +		}
> +		fallthrough;
>  	default:
>  		WARN_ON_ONCE(1);
>  		break;
> -- 
> 2.30.0
> 
> 

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  parent reply	other threads:[~2021-02-16 13:14 UTC|newest]

Thread overview: 28+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-02-07 17:09 [Ocfs2-devel] [PATCH 0/7] fsdax, xfs: Add reflink&dedupe support for fsdax Shiyang Ruan
2021-02-07 17:09 ` [Ocfs2-devel] [PATCH 1/7] fsdax: Output address in dax_iomap_pfn() and rename it Shiyang Ruan
2021-02-08 15:11   ` Christoph Hellwig
2021-02-22  7:44   ` Xiaoguang Wang
2021-02-23  1:32     ` [Ocfs2-devel] 回复: " ruansy.fnst
2021-02-07 17:09 ` [Ocfs2-devel] [PATCH 2/7] fsdax: Introduce dax_copy_edges() for CoW Shiyang Ruan
2021-02-08 15:11   ` Christoph Hellwig
2021-02-07 17:09 ` [Ocfs2-devel] [PATCH 3/7] fsdax: Copy data before write Shiyang Ruan
2021-02-08 15:14   ` Christoph Hellwig
2021-02-09  1:53     ` Ruan Shiyang
2021-02-07 17:09 ` [Ocfs2-devel] [PATCH 4/7] fsdax: Replace mmap entry in case of CoW Shiyang Ruan
2021-02-08 15:16   ` Christoph Hellwig
2021-02-16 13:11   ` David Sterba [this message]
2021-02-17  3:06     ` Ruan Shiyang
2021-02-07 17:09 ` [Ocfs2-devel] [PATCH 5/7] fsdax: Dedup file range to use a compare function Shiyang Ruan
2021-02-08 15:19   ` Christoph Hellwig
2021-02-09  9:15     ` Ruan Shiyang
2021-02-09  9:34       ` Christoph Hellwig
2021-02-09  9:46         ` Ruan Shiyang
2021-02-10 13:19           ` Christoph Hellwig
2021-02-17  3:24             ` Ruan Shiyang
2021-02-18 16:20               ` Darrick J. Wong
2021-02-25  7:35                 ` Christoph Hellwig
2021-02-07 17:09 ` [Ocfs2-devel] [PATCH 6/7] fs/xfs: Handle CoW for fsdax write() path Shiyang Ruan
2021-02-08 15:24   ` Christoph Hellwig
2021-02-07 17:09 ` [Ocfs2-devel] [PATCH 7/7] fs/xfs: Add dedupe support for fsdax Shiyang Ruan
2021-02-08 15:39 ` [Ocfs2-devel] [PATCH 0/7] fsdax, xfs: Add reflink&dedupe " Jan Kara
2021-02-09  1:50   ` Ruan Shiyang

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