linux-kernel - Re: [f2fs-dev] [PATCH v6] f2fs: compress: support compress level

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Message-ID: <15afffcc-636d-b678-0c01-b2fad98d9311@huawei.com>
Date:   Fri, 4 Dec 2020 11:11:03 +0800
From:   Chao Yu <yuchao0@...wei.com>
To:     Gao Xiang <hsiangkao@...hat.com>
CC:     Eric Biggers <ebiggers@...nel.org>, <jaegeuk@...nel.org>,
        <linux-kernel@...r.kernel.org>,
        <linux-f2fs-devel@...ts.sourceforge.net>
Subject: Re: [f2fs-dev] [PATCH v6] f2fs: compress: support compress level

On 2020/12/4 10:47, Gao Xiang wrote:
> On Fri, Dec 04, 2020 at 10:38:08AM +0800, Chao Yu wrote:
>> On 2020/12/4 10:06, Gao Xiang wrote:
>>> On Fri, Dec 04, 2020 at 09:56:27AM +0800, Chao Yu wrote:
> 
> ...
> 
>>
>>>
>>> Keep lz4hc dirty data under writeback could block writeback, make kswapd
>>> busy, and direct memory reclaim path, I guess that's why rare online
>>> compression chooses it. My own premature suggestion is that it'd better
>>> to show the CR or performance benefits in advance, and prevent unprivileged
>>> users from using high-level lz4hc algorithm (to avoid potential system attack.)
>>> either from mount options or ioctl.
>>
>> Yes, I guess you are worry about destop/server scenario, as for android scenario,
>> all compression related flow can be customized, and I don't think we will use
>> online lz4hc compress; for other scenario, except the numbers, I need to add the
>> risk of using lz4hc algorithm in document.
> 
> Yes, I was saying the general scenario. My overall premature thought is that
> before releasing some brand new algorithm, it may be better to evaluate first
> it'd benefit to some scenarios first (either on CR or performance side, or
> why adding this?), or it would might cause lzo-rle likewise situation in the

Yeah, got your point.

> future (and add more dependency to algorithms, you might see BWT-based bzip2
> removal patch

Oops, is that really allowed? I don't this is a good idea...and I don't see there
are deletions from fs/ due to similar reason...

Thanks,

> https://lore.kernel.org/r/20201117223253.65920-1-alex_y_xu@yahoo.ca
> (since I personally don't think BWT is a good algorithm as well)... Just FYI
> ... If i'm wrong, kindly ignore me :)
> 
> Thanks,
> Gao Xiang
> 
>>
>> Thanks,
> 
> .
>