[f2fs-dev] [f2fs-devel] Why does f2fs not reduce disk space when compression is on?

[f2fs-dev] [f2fs-devel] Why does f2fs not reduce disk space when compression is on?

[Fengnan Chang]

I'm testing the f2fs data compression feature. I created a new FS with the flags extra_attr and compression,
use chattr -R +c on the test dir to enable compression for the directory. 
I found that when compression was turned on, the files did not take up any less space.
Using trace, I see that the data is indeed compressed.
Is there a mistake in my testing method, or is this how it was designed and why?

This is my test method:

# mount
/dev/nvme0n1 on /mnt type f2fs (rw,lazytime,relatime,background_gc=on,discard,no_heap,user_xattr,inline_xattr,acl,inline_data,inline_dentry,flush_merge,extent_cache,mode=adaptive,active_logs=6,alloc_mode=reuse,fsync_mode=posix,compress_algorithm=lz4,compress_log_size=2)
# df 
Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/root               114901    112444         0 100% /
devtmpfs                497436         0    497436   0% /dev
tmpfs                   500060         0    500060   0% /dev/shm
tmpfs                   500060        52    500008   0% /tmp
tmpfs                   500060        20    500040   0% /run
/dev/nvme0n1          10483712    499724   9983988   5% /mnt
# mkdir test
# chattr -R +c test/
# dd if=/dev/zero of=/mnt/test/file bs=1M count=100
# sync
# df
Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/root               114901    112444         0 100% /
devtmpfs                497436         0    497436   0% /dev
tmpfs                   500060         0    500060   0% /dev/shm
tmpfs                   500060       368    499692   0% /tmp
tmpfs                   500060        20    500040   0% /run
/dev/nvme0n1          10483712    602232   9881480   6% /mnt


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Re: [f2fs-dev] [f2fs-devel] Why does f2fs not reduce disk space when compression is on?

[Chao Yu]

On 2021/4/12 21:13, Fengnan Chang wrote:
> I'm testing the f2fs data compression feature. I created a new FS with the flags extra_attr and compression,
> use chattr -R +c on the test dir to enable compression for the directory.
> I found that when compression was turned on, the files did not take up any less space.
> Using trace, I see that the data is indeed compressed.
> Is there a mistake in my testing method, or is this how it was designed and why?

https://lore.kernel.org/lkml/20200130185335.GA225399@google.com/

I guess we should document it well in f2fs.rst to avoid any confusion,
let me post a patch for that soon.

Thanks,

> 
> This is my test method:
> 
> # mount
> /dev/nvme0n1 on /mnt type f2fs (rw,lazytime,relatime,background_gc=on,discard,no_heap,user_xattr,inline_xattr,acl,inline_data,inline_dentry,flush_merge,extent_cache,mode=adaptive,active_logs=6,alloc_mode=reuse,fsync_mode=posix,compress_algorithm=lz4,compress_log_size=2)
> # df
> Filesystem           1K-blocks      Used Available Use% Mounted on
> /dev/root               114901    112444         0 100% /
> devtmpfs                497436         0    497436   0% /dev
> tmpfs                   500060         0    500060   0% /dev/shm
> tmpfs                   500060        52    500008   0% /tmp
> tmpfs                   500060        20    500040   0% /run
> /dev/nvme0n1          10483712    499724   9983988   5% /mnt
> # mkdir test
> # chattr -R +c test/
> # dd if=/dev/zero of=/mnt/test/file bs=1M count=100
> # sync
> # df
> Filesystem           1K-blocks      Used Available Use% Mounted on
> /dev/root               114901    112444         0 100% /
> devtmpfs                497436         0    497436   0% /dev
> tmpfs                   500060         0    500060   0% /dev/shm
> tmpfs                   500060       368    499692   0% /tmp
> tmpfs                   500060        20    500040   0% /run
> /dev/nvme0n1          10483712    602232   9881480   6% /mnt
> 
> 
> _______________________________________________
> Linux-f2fs-devel mailing list
> Linux-f2fs-devel@lists.sourceforge.net
> https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
> .
> 


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[f2fs-dev] 答复: [f2fs-devel] Why does f2fs not reduce disk space when compression is on?

[changfengnan]

Thanks, I got it.


-----邮件原件-----
发件人: Chao Yu <yuchao0@huawei.com>
发送时间: 2021年4月13日 9:16
收件人: Fengnan Chang <changfengnan@vivo.com>
抄送: jaegeuk@kernel.org; chao@kernel.org;
linux-f2fs-devel@lists.sourceforge.net
主题: Re: [f2fs-dev] [f2fs-devel] Why does f2fs not reduce disk space when
compression is on?

On 2021/4/12 21:13, Fengnan Chang wrote:
> I'm testing the f2fs data compression feature. I created a new FS with
> the flags extra_attr and compression, use chattr -R +c on the test dir
to enable compression for the directory.
> I found that when compression was turned on, the files did not take up
any less space.
> Using trace, I see that the data is indeed compressed.
> Is there a mistake in my testing method, or is this how it was designed
and why?

https://lore.kernel.org/lkml/20200130185335.GA225399@google.com/

I guess we should document it well in f2fs.rst to avoid any confusion, let
me post a patch for that soon.

Thanks,

>
> This is my test method:
>
> # mount
> /dev/nvme0n1 on /mnt type f2fs
> (rw,lazytime,relatime,background_gc=on,discard,no_heap,user_xattr,inli
> ne_xattr,acl,inline_data,inline_dentry,flush_merge,extent_cache,mode=a
> daptive,active_logs=6,alloc_mode=reuse,fsync_mode=posix,compress_algor
> ithm=lz4,compress_log_size=2)
> # df
> Filesystem           1K-blocks      Used Available Use% Mounted on
> /dev/root               114901    112444         0 100% /
> devtmpfs                497436         0    497436   0% /dev
> tmpfs                   500060         0    500060   0% /dev/shm
> tmpfs                   500060        52    500008   0% /tmp
> tmpfs                   500060        20    500040   0% /run
> /dev/nvme0n1          10483712    499724   9983988   5% /mnt
> # mkdir test
> # chattr -R +c test/
> # dd if=/dev/zero of=/mnt/test/file bs=1M count=100 # sync # df
> Filesystem           1K-blocks      Used Available Use% Mounted on
> /dev/root               114901    112444         0 100% /
> devtmpfs                497436         0    497436   0% /dev
> tmpfs                   500060         0    500060   0% /dev/shm
> tmpfs                   500060       368    499692   0% /tmp
> tmpfs                   500060        20    500040   0% /run
> /dev/nvme0n1          10483712    602232   9881480   6% /mnt
>
>
> _______________________________________________
> Linux-f2fs-devel mailing list
> Linux-f2fs-devel@lists.sourceforge.net
> https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
> .
>






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