Re: [PATCH v5 2/2] erofs: boost negative xattr lookup with bloom filter

[Gao Xiang <xiang@kernel.org>]

On Fri, Jul 21, 2023 at 06:49:23PM +0800, Jingbo Xu wrote:
> Optimise the negative xattr lookup with bloom filter.
> 
> The bit value for the bloom filter map has a reverse semantics for
> compatibility.  That is, the bit value of 0 indicates existence, while
> the bit value of 1 indicates the absence of corresponding xattr.
> 
> The initial version is _only_ enabled when xattr_filter_reserved is
> zero.  The filter map internals may change in the future, in which case
> the reserved flag will be set non-zero and we don't need bothering the
> compatible bits again at that time.  For now disable the optimization if
> this reserved flag is non-zero.
> 
> Signed-off-by: Jingbo Xu <jefflexu@linux.alibaba.com>
> ---
>  fs/erofs/Kconfig    |  1 +
>  fs/erofs/internal.h |  3 +++
>  fs/erofs/super.c    |  1 +
>  fs/erofs/xattr.c    | 14 ++++++++++++++
>  4 files changed, 19 insertions(+)
> 
> diff --git a/fs/erofs/Kconfig b/fs/erofs/Kconfig
> index f259d92c9720..f49669def828 100644
> --- a/fs/erofs/Kconfig
> +++ b/fs/erofs/Kconfig
> @@ -38,6 +38,7 @@ config EROFS_FS_DEBUG
>  config EROFS_FS_XATTR
>  	bool "EROFS extended attributes"
>  	depends on EROFS_FS
> +	select XXHASH
>  	default y
>  	help
>  	  Extended attributes are name:value pairs associated with inodes by
> diff --git a/fs/erofs/internal.h b/fs/erofs/internal.h
> index 36e32fa542f0..3c1f89d8421b 100644
> --- a/fs/erofs/internal.h
> +++ b/fs/erofs/internal.h
> @@ -151,6 +151,7 @@ struct erofs_sb_info {
>  	u32 xattr_prefix_start;
>  	u8 xattr_prefix_count;
>  	struct erofs_xattr_prefix_item *xattr_prefixes;
> +	unsigned int xattr_filter_reserved;
>  #endif
>  	u16 device_id_mask;	/* valid bits of device id to be used */
>  
> @@ -251,6 +252,7 @@ EROFS_FEATURE_FUNCS(fragments, incompat, INCOMPAT_FRAGMENTS)
>  EROFS_FEATURE_FUNCS(dedupe, incompat, INCOMPAT_DEDUPE)
>  EROFS_FEATURE_FUNCS(xattr_prefixes, incompat, INCOMPAT_XATTR_PREFIXES)
>  EROFS_FEATURE_FUNCS(sb_chksum, compat, COMPAT_SB_CHKSUM)
> +EROFS_FEATURE_FUNCS(xattr_filter, compat, COMPAT_XATTR_FILTER)
>  
>  /* atomic flag definitions */
>  #define EROFS_I_EA_INITED_BIT	0
> @@ -270,6 +272,7 @@ struct erofs_inode {
>  	unsigned char inode_isize;
>  	unsigned int xattr_isize;
>  
> +	unsigned int xattr_name_filter;
>  	unsigned int xattr_shared_count;
>  	unsigned int *xattr_shared_xattrs;
>  
> diff --git a/fs/erofs/super.c b/fs/erofs/super.c
> index 9d6a3c6158bd..72122323300e 100644
> --- a/fs/erofs/super.c
> +++ b/fs/erofs/super.c
> @@ -388,6 +388,7 @@ static int erofs_read_superblock(struct super_block *sb)
>  	sbi->xattr_blkaddr = le32_to_cpu(dsb->xattr_blkaddr);
>  	sbi->xattr_prefix_start = le32_to_cpu(dsb->xattr_prefix_start);
>  	sbi->xattr_prefix_count = dsb->xattr_prefix_count;
> +	sbi->xattr_filter_reserved = dsb->xattr_filter_reserved;
>  #endif
>  	sbi->islotbits = ilog2(sizeof(struct erofs_inode_compact));
>  	sbi->root_nid = le16_to_cpu(dsb->root_nid);
> diff --git a/fs/erofs/xattr.c b/fs/erofs/xattr.c
> index 40178b6e0688..e9b9ed6b28d2 100644
> --- a/fs/erofs/xattr.c
> +++ b/fs/erofs/xattr.c
> @@ -5,6 +5,7 @@
>   * Copyright (C) 2021-2022, Alibaba Cloud
>   */
>  #include <linux/security.h>
> +#include <linux/xxhash.h>
>  #include "xattr.h"
>  
>  struct erofs_xattr_iter {
> @@ -87,6 +88,7 @@ static int erofs_init_inode_xattrs(struct inode *inode)
>  	}
>  
>  	ih = it.kaddr + erofs_blkoff(sb, it.pos);
> +	vi->xattr_name_filter = le32_to_cpu(ih->h_name_filter);
>  	vi->xattr_shared_count = ih->h_shared_count;
>  	vi->xattr_shared_xattrs = kmalloc_array(vi->xattr_shared_count,
>  						sizeof(uint), GFP_KERNEL);
> @@ -392,7 +394,10 @@ int erofs_getxattr(struct inode *inode, int index, const char *name,
>  		   void *buffer, size_t buffer_size)
>  {
>  	int ret;
> +	uint32_t hashbit;

Why using `uint32_t` here rather than `unsigned int`? We don't use
`uint32_t` in the kernel codebase.

Thanks,
Gao Xiang