Date: Wed, 6 Apr 2016 15:42:55 -0500 From: Leo Prasath Arulraj <leo.prasath@gmail.com> To: freebsd-fs@freebsd.org Subject: Does ZFS or UFS classify FS Metatada I/O requests with specific BIO_META like flag? Message-ID: <CAFcURvMJ4i0qOJ2cvXuiwoK0tQume1j9rQTr09W0TqQkCow3Yg@mail.gmail.com>
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Linux file systems pass down a metadata flag with block i/o requests so that the device driver below the file system have this information. This flag could be set on those block I/O requests that the file system issues to file system metadata information like FS inodes, journal , block allocation bitmaps etc. on the disk. Examples: 1) Ext3: This thread here : http://lists.linuxfoundation.org/pipermail/containers/2009-April/017126.html says ext3 file system sets this flag on metadata i/o requests so that it is prioritized over data i/o requests in the I/O controller for the disk. 2) Ext4: This thread tells how ext4 tags all journal i/o with the metadata flag : http://www.spinics.net/lists/linux-ext4/msg18213.html 3) XFS: This thread says XFS file system tags metadata I/O requests for better merging: http://oss.sgi.com/pipermail/xfs/2009-November/004631.html I want to know if the FreeBSD filesystem UFS and ZFS set any such flag. >From a skim through the source code, it does not seem so because the bio structure itself does not have any such flag in the first place : http://fxr.watson.org/fxr/source/sys/bio.h?v=FREEBSD10#L143,144 I approciate any help regarding this. Thanks, Leo
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