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Date:   Fri, 5 Jul 2019 00:46:15 +0800
From:   Gao Xiang <>
To:     Greg Kroah-Hartman <>,
        Gao Xiang <>
Cc:, Theodore Ts'o <>,, LKML <>,
        Linus Torvalds <>,
        Alexander Viro <>,,
        Andrew Morton <>,
        Miao Xie <>
Subject: Re: [PATCH] erofs: promote erofs from staging

On 2019/7/4 ????10:18, Greg Kroah-Hartman wrote:
> On Thu, Jul 04, 2019 at 10:00:53PM +0800, Gao Xiang wrote:
>> Hi Greg,
>> On 2019/7/4 21:50, Greg Kroah-Hartman wrote:
>>> On Thu, Jul 04, 2019 at 09:34:13PM +0800, Gao Xiang wrote:
>>>> EROFS file system has been in Linux-staging for about a year.
>>>> It has been proved to be stable enough to move out of staging
>>>> by 10+ millions of HUAWEI Android mobile phones on the market
>>>> from EMUI 9.0.1, and it was promoted as one of the key features
>>>> of EMUI 9.1 [1], including P30(pro).
>>>> EROFS is a read-only file system designed to save extra storage
>>>> space with guaranteed end-to-end performance by applying
>>>> fixed-size output compression, inplace I/O and decompression
>>>> inplace technologies [2] to Linux filesystem.
>>>> In our observation, EROFS is one of the fastest Linux compression
>>>> filesystem using buffered I/O in the world. It will support
>>>> direct I/O in the future if needed. EROFS even has better read
>>>> performance in a large CR range compared with generic uncompressed
>>>> file systems with proper CPU-storage combination, which is
>>>> a reason why erofs can be landed to speed up mobile phone
>>>> performance, and which can be probably used for other use cases
>>>> such as LiveCD and Docker image as well.
>>>> Currently erofs supports 4k LZ4 fixed-size output compression
>>>> since LZ4 is the fastest widely-used decompression solution in
>>>> the world and 4k leads to unnoticable read amplification for
>>>> the worst case. More compression algorithms and cluster sizes
>>>> could be added later, which depends on the real requirement.
>>>> More informations about erofs itself are available at:
>>>>  Documentation/filesystems/erofs.txt
>>>> erofs-utils (mainly mkfs.erofs now) is available at
>>>> git://
>>>> Preliminary iomap support has been pending in erofs mailing
>>>> list by Chao Yu. The key issue is that current iomap doesn't
>>>> support tail-end packing inline data yet, it should be
>>>> resolved later.
>>>> Thanks to many contributors in the last year, the code is more
>>>> clean and improved. We hope erofs can be used in wider use cases
>>>> so let's promote erofs out of staging and enhance it more actively.
>>>> Share comments about erofs! We think erofs is useful to
>>>> community as a part of Linux upstream :)
>>> I don't know if this format is easy for the linux-fsdevel people to
>>> review, it forces them to look at the in-kernel code, which makes it
>>> hard to quote.
>>> Perhaps just make a patch that adds the filesystem to the tree and after
>>> it makes it through review, I can delete the staging version?  We've
>>> been doing that for wifi drivers that move out of staging as it seems to
>>> be a bit easier.
>> OK, I will resend the whole patchset later as you suggested, but it will
>> lack of information about some original authors and I'd like to know who
>> is responsible to merge this kind of request to Linux upstream... maybe Linus?
> I don't know who adds new filesystems to the tree these days.  Usually
> you need to get some acks from the fsdevel developers first, and then it
> can go directly to Linus in one of the merge windows.

Hope that fs guys could eventually take some glances / time on erofs
since it's more useful than romfs/cramfs/squashfs for read-only
performance scenario since storage space is not tight and slow than 10
years before, even for some embedded devices such as mobile phones/pads.
and compression file system could not be designed for saving storage
space only like these...

I think except for unzip_vle.c (which works fine, but not very cleaned
as other files), erofs is clean enough for reviewing...

>> And it could be more consistent to leave staging version for linux-5.3
>> because we still use it, but anyway, I will do it now.
> Yeah, it's too late for 5.3-rc1, so don't worry.  I'll not delete
> anything until it's actually in someone else's tree on its way to Linus.

Sound great, I will tidy the whole patchset up and hope it eventually be

Gao Xiang

> thanks,
> greg k-h

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