Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Thu, 14 Oct 2021 00:03:02 +0800
From:   Gao Xiang <hsiangkao@linux.alibaba.com>
To:     Yue Hu <zbestahu@163.com>
Cc:     Yue Hu <zbestahu@gmail.com>, xiang@kernel.org, chao@kernel.org,
        linux-erofs@lists.ozlabs.org, linux-kernel@vger.kernel.org,
        huyue2@yulong.com, zhangwen@yulong.com
Subject: Re: [PATCH] erofs: fix the per-CPU buffer decompression for small
 output size
Message-ID: <YWcDNrHBYTQIq6x+@B-P7TQMD6M-0146.local>
References: <20211013092906.1434-1-zbestahu@gmail.com>
 <YWbIWydks+wpuNij@B-P7TQMD6M-0146.local>
 <20211013211005.7bd9fc08.zbestahu@163.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
In-Reply-To: <20211013211005.7bd9fc08.zbestahu@163.com>
Precedence: bulk

On Wed, Oct 13, 2021 at 09:10:05PM +0800, Yue Hu wrote:
> Hi Xiang,
> 
> On Wed, 13 Oct 2021 19:51:55 +0800
> Gao Xiang <hsiangkao@linux.alibaba.com> wrote:
> 
> > Hi Yue,
> > 
> > On Wed, Oct 13, 2021 at 05:29:05PM +0800, Yue Hu wrote:
> > > From: Yue Hu <huyue2@yulong.com>
> > > 
> > > Note that z_erofs_lz4_decompress() will return a positive value if
> > > decompression succeeds. However, we do not copy_from_pcpubuf() due
> > > to !ret. Let's fix it.
> > > 
> > > Signed-off-by: Yue Hu <huyue2@yulong.com>  
> > 
> > Thanks for catching this. This is a valid issue, but it has no real
> > impact to the current kernels since such pcluster in practice will be
> > !inplace_io and trigger "if (nrpages_out == 1 && !rq->inplace_io) {"
> > above for upstream strategies.
> > 
> > Our customized lz4 implementation will return 0 if success instead, so
> > it has no issue to our previous products as well.
> 
> Yes, i just find the issue when i try to implement a new feature of
> tail-packing inline compressed data. No problem in my current version.

Yeah, please help update the return value of z_erofs_lz4_decompress()
and get rid of such unneeded fast path.

Thanks,
Gao Xiang

> 
> Thanks.
> 
> > 
> > For such cases, how about updating z_erofs_lz4_decompress() to return
> > 0 if success instead rather than outputsize. Since I'll return 0 if
> > success for LZMA as well.
> > 
> > Thanks,
> > Gao Xiang
>