Re: Strange compress behavior under /usr

[Qiyu Yan]

在 2021-05-11星期二的 22:57 +0800，Qiyu Yan写道：
>  Dear folks, 
>  
>  My problem is that new file created at /usr won't be compressed.
>  
>  I accenticly that none of my files under /usr is compressed[1], so I
>  tried to run `sudo btrfs fi def -czstd -v -r /usr` to compress them,
>  that seems to work. And `sudo compsize /usr` now gives
>  Processed 431312 files, 224528 regular extents (230971 refs), 253758
>  inline.
>  Type       Perc     Disk Usage   Uncompressed Referenced  
>  TOTAL       56%      7.2G          12G          13G       
>  none       100%      3.5G         3.5G         3.5G       
>  zstd        39%      3.6G         9.2G         9.7G 
>  
>  This seems pretty good, but when I am testing dding to dump a file to
>  /usr to test compress for new file, problem happens:
>  
>  [root@yan-desktop /]# dd if=/dev/zero of=/usr/1 bs=10240 count=10000
>  记录了10000+0 的读入
>  记录了10000+0 的写出
>  102400000字节（102 MB，98 MiB）已复制，0.0426441 s，2.4 GB/s
>  [root@yan-desktop /]# dd if=/dev/zero of=/etc/1 bs=10240 count=10000
>  记录了10000+0 的读入
>  记录了10000+0 的写出
>  102400000字节（102 MB，98 MiB）已复制，0.0585055 s，1.8 GB/s
>  [root@yan-desktop /]# compsize /usr/1
>  Processed 1 file, 1 regular extents (1 refs), 0 inline.
>  Type       Perc     Disk Usage   Uncompressed Referenced  
>  TOTAL      100%       97M          97M          97M       
>  none       100%       97M          97M          97M       
>  [root@yan-desktop /]# compsize /etc/1
>  Processed 1 file, 782 regular extents (782 refs), 0 inline.
>  Type       Perc     Disk Usage   Uncompressed Referenced  
>  TOTAL        3%      3.0M          97M          97M       
>  zstd         3%      3.0M          97M          97M       
>  
>  Just ignore those Chinese output by dd, it doesn't important... But
>  as
>  you can see: file created at /usr/1 is not compressed at all while
>  file
>  created at /etc/1 gets compressed. There should not be any difficult
>  to
>  compress all-zero contents for zstd.
>  
>  There should not be so much difference between /usr and /etc, they
>  are
>  in same subvolume named "root" mounted at /.
>  
>  [root@yan-desktop /]# btrfs su li /
>  ID 256 gen 1530662 top level 5 path home
>  ID 257 gen 1530662 top level 5 path root
>  ID 266 gen 1530614 top level 257 path var/lib/machines
>  ID 292 gen 1530585 top level 257 path var/lib/mock
>  ...[some container storage subvolumes]
>  
>  and mount options for / is
>  rw,noatime,seclabel,compress=zstd:3,ssd,space_cache=v2,subvolid=257,s
>  ub
>  vol=/root (subvol=root,noatime,compress=zstd in fstab)
>  
>  lsattr /|grep -E "var|etc" gives
>  -------------------- /etc
>  -------------------- /var
>  
>  `btrfs property get /usr` or `btrfs property get /etc` gives empty
>  output.
>  
>  How do I troubleshoot this problem?
>  
>  [1] That is also a problem since I setup compress after upgrading to
>  fedora 34, and have done many package updates since then. So new
>  extents written to /usr should be compressed while compsize reports
>  none of them.
>   
And by setting compress-force=zstd, new files in /usr will get
compressed as expected. I suspect there to be something wrong with the
compressible check process builtin in btrfs? 
-- 
Qiyu Yan
GPG keyid: 0x4FC914F065F2DF12
About: https://fedoraproject.org/wiki/User:Yanqiyu