linux-kernel - Re: [PATCH v9 17/21] erofs: implement fscache-based metadata read

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Message-ID: <YmFWD7otjEb/SMPJ@B-P7TQMD6M-0146.local>
Date:   Thu, 21 Apr 2022 21:03:11 +0800
From:   Gao Xiang <hsiangkao@...ux.alibaba.com>
To:     Jeffle Xu <jefflexu@...ux.alibaba.com>
Cc:     dhowells@...hat.com, linux-cachefs@...hat.com, xiang@...nel.org,
        chao@...nel.org, linux-erofs@...ts.ozlabs.org,
        torvalds@...ux-foundation.org, gregkh@...uxfoundation.org,
        willy@...radead.org, linux-fsdevel@...r.kernel.org,
        joseph.qi@...ux.alibaba.com, bo.liu@...ux.alibaba.com,
        tao.peng@...ux.alibaba.com, gerry@...ux.alibaba.com,
        eguan@...ux.alibaba.com, linux-kernel@...r.kernel.org,
        luodaowen.backend@...edance.com, tianzichen@...ishou.com,
        fannaihao@...du.com, zhangjiachen.jaycee@...edance.com
Subject: Re: [PATCH v9 17/21] erofs: implement fscache-based metadata read

On Fri, Apr 15, 2022 at 08:36:10PM +0800, Jeffle Xu wrote:
> Implement the data plane of reading metadata from primary data blob
> over fscache.
> 
> Signed-off-by: Jeffle Xu <jefflexu@...ux.alibaba.com>
> ---
>  fs/erofs/data.c    | 19 +++++++++++++++----
>  fs/erofs/fscache.c | 27 +++++++++++++++++++++++++++
>  2 files changed, 42 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/erofs/data.c b/fs/erofs/data.c
> index 14b64d960541..bb9c1fd48c19 100644
> --- a/fs/erofs/data.c
> +++ b/fs/erofs/data.c
> @@ -6,6 +6,7 @@
>   */
>  #include "internal.h"
>  #include <linux/prefetch.h>
> +#include <linux/sched/mm.h>
>  #include <linux/dax.h>
>  #include <trace/events/erofs.h>
>  
> @@ -35,14 +36,20 @@ void *erofs_bread(struct erofs_buf *buf, struct inode *inode,
>  	erofs_off_t offset = blknr_to_addr(blkaddr);
>  	pgoff_t index = offset >> PAGE_SHIFT;
>  	struct page *page = buf->page;
> +	struct folio *folio;
> +	unsigned int nofs_flag;
>  
>  	if (!page || page->index != index) {
>  		erofs_put_metabuf(buf);
> -		page = read_cache_page_gfp(mapping, index,
> -				mapping_gfp_constraint(mapping, ~__GFP_FS));
> -		if (IS_ERR(page))
> -			return page;
> +
> +		nofs_flag = memalloc_nofs_save();
> +		folio = read_cache_folio(mapping, index, NULL, NULL);
> +		memalloc_nofs_restore(nofs_flag);
> +		if (IS_ERR(folio))
> +			return folio;
> +
>  		/* should already be PageUptodate, no need to lock page */
> +		page = folio_file_page(folio, index);
>  		buf->page = page;
>  	}
>  	if (buf->kmap_type == EROFS_NO_KMAP) {
> @@ -63,6 +70,10 @@ 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))
> +		return erofs_bread(buf, EROFS_SB(sb)->s_fscache->inode,
> +				   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 066f68c062e2..3f00eb34ac35 100644
> --- a/fs/erofs/fscache.c
> +++ b/fs/erofs/fscache.c
> @@ -58,7 +58,34 @@ 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 folio *folio = page_folio(page);
> +	struct super_block *sb = folio_mapping(folio)->host->i_sb;
> +	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_mapping(folio), folio_pos(folio),
> +			folio_size(folio), mdev.m_pa);
> +	if (ret)
> +		goto out;
> +
> +	folio_mark_uptodate(folio);

	if (!ret)
		folio_mark_uptodate(folio);

Thanks,
Gao Xiang

> +out:
> +	folio_unlock(folio);
> +	return ret;
> +}
> +
>  static const struct address_space_operations erofs_fscache_meta_aops = {
> +	.readpage = erofs_fscache_meta_readpage,
>  };
>  
>  /*
> -- 
> 2.27.0