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

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Message-ID: <a8b9a758-d469-b9a6-f5e8-8f3768e2ea81@linux.alibaba.com>
Date:   Mon, 17 Apr 2023 15:12:31 +0800
From:   Gao Xiang <hsiangkao@...ux.alibaba.com>
To:     Yue Hu <zbestahu@...il.com>
Cc:     xiang@...nel.org, chao@...nel.org, linux-erofs@...ts.ozlabs.org,
        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 15:15, Yue Hu wrote:
> On Mon, 17 Apr 2023 15:00:25 +0800
> Gao Xiang <hsiangkao@...ux.alibaba.com> wrote:
> 

..

>>
>> Although please help refine the comment below:
>>
>> 	/* scan & fill inplace I/O pages in the reverse order */
> 
> Ok, will refine it in v2.

I rethink this, I don't want to go far in this way, and this makes a
O(n) scan into O(n^2) when a single inplace I/O page is added.

So sorry, I don't think it's a good way, although I also don't think
`icur` is a good name and we might need to find a better name.

Thanks,
Gao Xiang

> 
>>
>> Thanks,
>> Gao Xiang
>>
>>>> +    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;
>>>>    }