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Date:   Thu, 7 Apr 2022 22:19:28 +0800
From:   Gao Xiang <xiang@kernel.org>
To:     Jeffle Xu <jefflexu@linux.alibaba.com>
Cc:     dhowells@redhat.com, linux-cachefs@redhat.com, xiang@kernel.org,
        chao@kernel.org, linux-erofs@lists.ozlabs.org,
        torvalds@linux-foundation.org, gregkh@linuxfoundation.org,
        willy@infradead.org, linux-fsdevel@vger.kernel.org,
        joseph.qi@linux.alibaba.com, bo.liu@linux.alibaba.com,
        tao.peng@linux.alibaba.com, gerry@linux.alibaba.com,
        eguan@linux.alibaba.com, linux-kernel@vger.kernel.org,
        luodaowen.backend@bytedance.com, tianzichen@kuaishou.com,
        fannaihao@baidu.com
Subject: Re: [PATCH v8 16/20] erofs: implement fscache-based metadata read
Message-ID: <Yk7y8FuBosbtAY3l@debian>
Mail-Followup-To: Jeffle Xu <jefflexu@linux.alibaba.com>,
        dhowells@redhat.com, linux-cachefs@redhat.com, xiang@kernel.org,
        chao@kernel.org, linux-erofs@lists.ozlabs.org,
        torvalds@linux-foundation.org, gregkh@linuxfoundation.org,
        willy@infradead.org, linux-fsdevel@vger.kernel.org,
        joseph.qi@linux.alibaba.com, bo.liu@linux.alibaba.com,
        tao.peng@linux.alibaba.com, gerry@linux.alibaba.com,
        eguan@linux.alibaba.com, linux-kernel@vger.kernel.org,
        luodaowen.backend@bytedance.com, tianzichen@kuaishou.com,
        fannaihao@baidu.com
References: <20220406075612.60298-1-jefflexu@linux.alibaba.com>
 <20220406075612.60298-17-jefflexu@linux.alibaba.com>
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In-Reply-To: <20220406075612.60298-17-jefflexu@linux.alibaba.com>
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On Wed, Apr 06, 2022 at 03:56:08PM +0800, Jeffle Xu wrote:
> Implement the data plane of reading metadata from primary data blob
> over fscache.
> 
> Signed-off-by: Jeffle Xu <jefflexu@linux.alibaba.com>
> ---
>  fs/erofs/data.c     | 20 ++++++++++++++++++--
>  fs/erofs/fscache.c  | 38 ++++++++++++++++++++++++++++++++++++++
>  fs/erofs/internal.h |  9 +++++++++
>  3 files changed, 65 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/erofs/data.c b/fs/erofs/data.c
> index 14b64d960541..cb8fe299ad67 100644
> --- a/fs/erofs/data.c
> +++ b/fs/erofs/data.c
> @@ -31,15 +31,26 @@ void erofs_put_metabuf(struct erofs_buf *buf)
>  void *erofs_bread(struct erofs_buf *buf, struct inode *inode,
>  		  erofs_blk_t blkaddr, enum erofs_kmap_type type)
>  {
> -	struct address_space *const mapping = inode->i_mapping;
>  	erofs_off_t offset = blknr_to_addr(blkaddr);
>  	pgoff_t index = offset >> PAGE_SHIFT;
>  	struct page *page = buf->page;
>  
>  	if (!page || page->index != index) {
>  		erofs_put_metabuf(buf);
> -		page = read_cache_page_gfp(mapping, index,
> +		if (buf->sb) {
> +			struct folio *folio;
> +
> +			folio = erofs_fscache_get_folio(buf->sb, index);
> +			if (IS_ERR(folio))
> +				page = ERR_CAST(folio);
> +			else
> +				page = folio_page(folio, 0);
> +		} else {
> +			struct address_space *const mapping = inode->i_mapping;
> +
> +			page = read_cache_page_gfp(mapping, index,
>  				mapping_gfp_constraint(mapping, ~__GFP_FS));
> +		}
>  		if (IS_ERR(page))
>  			return page;
>  		/* should already be PageUptodate, no need to lock page */
> @@ -63,6 +74,11 @@ void *erofs_bread(struct erofs_buf *buf, struct inode *inode,
>  void *erofs_read_metabuf(struct erofs_buf *buf, struct super_block *sb,
>  			 erofs_blk_t blkaddr, enum erofs_kmap_type type)
>  {
> +	if (erofs_is_fscache_mode(sb)) {
> +		buf->sb = sb;
> +		return erofs_bread(buf, NULL, blkaddr, type);
> +	}
> +
>  	return erofs_bread(buf, sb->s_bdev->bd_inode, blkaddr, type);
>  }
>  
> diff --git a/fs/erofs/fscache.c b/fs/erofs/fscache.c
> index d38a6efc8e50..158cc273f8fb 100644
> --- a/fs/erofs/fscache.c
> +++ b/fs/erofs/fscache.c
> @@ -34,9 +34,47 @@ static int erofs_fscache_read_folios(struct fscache_cookie *cookie,
>  	return ret;
>  }
>  
> +static int erofs_fscache_meta_readpage(struct file *data, struct page *page)
> +{
> +	int ret;
> +	struct super_block *sb = (struct super_block *)data;
> +	struct folio *folio = page_folio(page);
> +	struct erofs_map_dev mdev = {
> +		.m_deviceid = 0,
> +		.m_pa = folio_pos(folio),
> +	};
> +
> +	ret = erofs_map_dev(sb, &mdev);
> +	if (ret)
> +		goto out;
> +
> +	ret = erofs_fscache_read_folios(mdev.m_fscache->cookie,
> +			folio_file_mapping(folio), folio_pos(folio),
> +			folio_size(folio), mdev.m_pa);
> +	if (ret)
> +		goto out;
> +
> +	folio_mark_uptodate(folio);
> +out:
> +	folio_unlock(folio);
> +	return ret;
> +}
> +
>  static const struct address_space_operations erofs_fscache_meta_aops = {
> +	.readpage = erofs_fscache_meta_readpage,
>  };
>  
> +/*
> + * Get the page cache of data blob at the index offset.
> + * Return: up to date page on success, ERR_PTR() on failure.
> + */

Unnecessary comment and even unnecessary helper.

Thanks,
Gao Xiang

> +struct folio *erofs_fscache_get_folio(struct super_block *sb, pgoff_t index)
> +{
> +	struct erofs_fscache *ctx = EROFS_SB(sb)->s_fscache;
> +
> +	return read_mapping_folio(ctx->inode->i_mapping, index, (void *)sb);
> +}
> +
>  /*
>   * Create an fscache context for data blob.
>   * Return: 0 on success and allocated fscache context is assigned to @fscache,
> diff --git a/fs/erofs/internal.h b/fs/erofs/internal.h
> index 90f7d6286a4f..e186051f0640 100644
> --- a/fs/erofs/internal.h
> +++ b/fs/erofs/internal.h
> @@ -276,6 +276,7 @@ enum erofs_kmap_type {
>  };
>  
>  struct erofs_buf {
> +	struct super_block *sb;
>  	struct page *page;
>  	void *base;
>  	enum erofs_kmap_type kmap_type;
> @@ -639,6 +640,8 @@ int erofs_fscache_register_cookie(struct super_block *sb,
>  				  struct erofs_fscache **fscache,
>  				  char *name, bool need_inode);
>  void erofs_fscache_unregister_cookie(struct erofs_fscache **fscache);
> +
> +struct folio *erofs_fscache_get_folio(struct super_block *sb, pgoff_t index);
>  #else
>  static inline int erofs_fscache_register_fs(struct super_block *sb) { return 0; }
>  static inline void erofs_fscache_unregister_fs(struct super_block *sb) {}
> @@ -653,6 +656,12 @@ static inline int erofs_fscache_register_cookie(struct super_block *sb,
>  static inline void erofs_fscache_unregister_cookie(struct erofs_fscache **fscache)
>  {
>  }
> +
> +static inline struct folio *erofs_fscache_get_folio(struct super_block *sb,
> +						    pgoff_t index)
> +{
> +	return ERR_PTR(-EOPNOTSUPP);
> +}
>  #endif
>  
>  #define EFSCORRUPTED    EUCLEAN         /* Filesystem is corrupted */
> -- 
> 2.27.0
>