[Cluster-devel] GFS2 file system does not invalidate page cache after direct IO write

Gang,

On Thu, May 4, 2017 at 5:33 AM, Gang He <[email protected]> wrote:
> Hello Guys,
>
> I found a interesting thing on GFS2 file system, After I did a direct IO write for a whole file, I still saw there were some page caches in this inode.
> It looks this GFS2 behavior does not follow file system POSIX semantics, I just want to know this problem belongs to a know issue or we can fix it?
> By the way, I did the same testing on EXT4 and OCFS2 file systems, the result looks OK.
> I will paste my testing command lines and outputs as below,
>
> For EXT4 file system,
> tb-nd1:/mnt/ext4 # rm -rf f3
> tb-nd1:/mnt/ext4 # dd if=/dev/urandom of=./f3 bs=1M count=4 oflag=direct
> 4+0 records in
> 4+0 records out
> 4194304 bytes (4.2 MB, 4.0 MiB) copied, 0.0393563 s, 107 MB/s
> tb-nd1:/mnt/ext4 # vmtouch -v f3
> f3
> [                                                         ] 0/1024
>
>            Files: 1
>      Directories: 0
>   Resident Pages: 0/1024  0/4M  0%
>          Elapsed: 0.000424 seconds
> tb-nd1:/mnt/ext4 #
>
> For OCFS2 file system,
> tb-nd1:/mnt/ocfs2 # rm -rf f3
> tb-nd1:/mnt/ocfs2 # dd if=/dev/urandom of=./f3 bs=1M count=4 oflag=direct
> 4+0 records in
> 4+0 records out
> 4194304 bytes (4.2 MB, 4.0 MiB) copied, 0.0592058 s, 70.8 MB/s
> tb-nd1:/mnt/ocfs2 # vmtouch -v f3
> f3
> [                                                         ] 0/1024
>
>            Files: 1
>      Directories: 0
>   Resident Pages: 0/1024  0/4M  0%
>          Elapsed: 0.000226 seconds
>
> For GFS2 file system,
> tb-nd1:/mnt/gfs2 # rm -rf f3
> tb-nd1:/mnt/gfs2 # dd if=/dev/urandom of=./f3 bs=1M count=4 oflag=direct
> 4+0 records in
> 4+0 records out
> 4194304 bytes (4.2 MB, 4.0 MiB) copied, 0.0579509 s, 72.4 MB/s
> tb-nd1:/mnt/gfs2 # vmtouch -v f3
> f3
> [             oo                         oOo              ] 48/1024

I cannot reproduce, at least not so easily. What kernel version is
this? If it's not a mainline kernel, can you reproduce on mainline?

Thanks,
Andreas