linux-kernel - Re: [PATCH] erofs: remove unneeded icur field from struct z_erofs_decompress

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Message-ID: <26cdf7b0-5d7d-68ba-da76-1ad800708946@linux.alibaba.com>
Date:   Mon, 17 Apr 2023 14:52:59 +0800
From:   Gao Xiang <hsiangkao@...ux.alibaba.com>
To:     Yue Hu <zbestahu@...il.com>, xiang@...nel.org, chao@...nel.org,
        linux-erofs@...ts.ozlabs.org
Cc:     jefflexu@...ux.alibaba.com, linux-kernel@...r.kernel.org,
        huyue2@...lpad.com, zhangwen@...lpad.com
Subject: Re: [PATCH] erofs: remove unneeded icur field from struct
 z_erofs_decompress_frontend



On 2023/4/17 14:41, Yue Hu wrote:
> From: Yue Hu <huyue2@...lpad.com>
> 
> The icur field is only used in z_erofs_try_inplace_io(). Let's just use
> a local variable instead. And no need to check if the pcluster is inline
> when setting icur since inline page cannot be used for inplace I/O.
> 
> Signed-off-by: Yue Hu <huyue2@...lpad.com>

Nope, it's a behavior change.
Other users could feed more inplace I/O pages before I/O submission
to reduce memory consumption, it's common when applying stress model
in low memory scenarios.

Thanks,
Gao Xiang

> ---
>   fs/erofs/zdata.c | 13 +++++--------
>   1 file changed, 5 insertions(+), 8 deletions(-)
> 
> diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c
> index f759152feffa..f8bf2b227942 100644
> --- a/fs/erofs/zdata.c
> +++ b/fs/erofs/zdata.c
> @@ -554,9 +554,6 @@ struct z_erofs_decompress_frontend {
>   	/* used for applying cache strategy on the fly */
>   	bool backmost;
>   	erofs_off_t headoffset;
> -
> -	/* a pointer used to pick up inplace I/O pages */
> -	unsigned int icur;
>   };
>   
>   #define DECOMPRESS_FRONTEND_INIT(__i) { \
> @@ -707,11 +704,13 @@ static bool z_erofs_try_inplace_io(struct z_erofs_decompress_frontend *fe,
>   				   struct z_erofs_bvec *bvec)
>   {
>   	struct z_erofs_pcluster *const pcl = fe->pcl;
> +	/* file-backed online pages are traversed in reverse order */
> +	unsigned int icur = pcl->pclusterpages;
>   
> -	while (fe->icur > 0) {
> -		if (!cmpxchg(&pcl->compressed_bvecs[--fe->icur].page,
> +	while (icur > 0) {
> +		if (!cmpxchg(&pcl->compressed_bvecs[--icur].page,
>   			     NULL, bvec->page)) {
> -			pcl->compressed_bvecs[fe->icur] = *bvec;
> +			pcl->compressed_bvecs[icur] = *bvec;
>   			return true;
>   		}
>   	}
> @@ -877,8 +876,6 @@ static int z_erofs_collector_begin(struct z_erofs_decompress_frontend *fe)
>   	}
>   	z_erofs_bvec_iter_begin(&fe->biter, &fe->pcl->bvset,
>   				Z_EROFS_INLINE_BVECS, fe->pcl->vcnt);
> -	/* since file-backed online pages are traversed in reverse order */
> -	fe->icur = z_erofs_pclusterpages(fe->pcl);
>   	return 0;
>   }
>