linux-kernel - Re: [PATCH v3 2/2] erofs: boost negative xattr lookup with bloom filter

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Message-ID: <042c1a3e-2004-c416-a368-b2f6676bb7c0@linux.alibaba.com>
Date:   Thu, 13 Jul 2023 11:34:45 +0800
From:   Gao Xiang <hsiangkao@...ux.alibaba.com>
To:     Jingbo Xu <jefflexu@...ux.alibaba.com>, chao@...nel.org,
        huyue2@...lpad.com, linux-erofs@...ts.ozlabs.org
Cc:     linux-kernel@...r.kernel.org, alexl@...hat.com
Subject: Re: [PATCH v3 2/2] erofs: boost negative xattr lookup with bloom
 filter



On 2023/7/12 19:51, 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.
> 
> This feature is enabled only when xattr_filter_reserved is non-zero.
> The on-disk format for the filter map 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@...ux.alibaba.com>
> ---
>   fs/erofs/internal.h |  3 +++
>   fs/erofs/super.c    |  1 +
>   fs/erofs/xattr.c    | 13 +++++++++++++
>   3 files changed, 17 insertions(+)
> 
> diff --git a/fs/erofs/internal.h b/fs/erofs/internal.h
> index 36e32fa542f0..ebcad25e3750 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 long 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..eb1d1974d4b3 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 bit;
>   	struct erofs_xattr_iter it;
> +	struct erofs_inode *vi = EROFS_I(inode);
> +	struct erofs_sb_info *sbi = EROFS_SB(inode->i_sb);
>   
>   	if (!name)
>   		return -EINVAL;
> @@ -401,6 +406,14 @@ int erofs_getxattr(struct inode *inode, int index, const char *name,
>   	if (ret)
>   		return ret;
>   
> +	/* the reserved flag is non-zero if hashing algorithm changes */
> +	if (erofs_sb_has_xattr_filter(sbi) && !sbi->xattr_filter_reserved) {
> +		bit = xxh32(name, strlen(name), EROFS_XATTR_FILTER_SEED + index);

should we enable xxh32 by using CONFIG_XXHASH?

Thanks,
Gao Xiang