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[RFD] xfs_fsr: Adding features for online defragmentation

To: xfs@xxxxxxxxxxx
Subject: [RFD] xfs_fsr: Adding features for online defragmentation
From: Somdeep Dey <somdeepdey10@xxxxxxxxx>
Date: Tue, 19 Aug 2014 23:14:27 +0530
Delivered-to: xfs@xxxxxxxxxxx
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We are a team of three final year under-graduates fromÂPune Institute
of Computer Technology, India and were looking for a project in XFSÂ
with a development time of about 6 - 7 months. On contacting Dave,Â
he suggested we work on the userspace utility, xfs_fsr.
xfs_fsr(online defragmenter):
A few possible enhancements to xfs_fsr are as follows:
1. explicit control of locality for groups of files.
2. ability to defragment only portions of files rather
than just whole files.
3. defragmenting free space.
4. enhanced/faster filesystem scanning.
Our understanding of the problem is as follows:
A) We identified the first thing needed, will be to find regions ofÂ
fragmented free space. Dave directed us to the following prototypeÂ
that he had written
B) ÂThe next task will be to go about finding the owners of the blocks
that are causing the region of fragmented free space. It will require a
reverse block map to do this efficiently. Dave has said that he is likely
to implement it in the next couple of months, and we understand that
we will to need to define the interfaces needed to query the rmap fromÂ
C) ÂOnce the fragmented free space, and the files that own the blocksÂ
that fragment the free space are found we will need to move them, andÂ
take care of the following:
(a) move just the blocks we need to.
(b) control exactly where we move them to.
We are reviewing the recent patches on the mailing list for IOC_MOV_DATA,Â
which allows an arbitrary range of one file to be swapped with an arbitrary
range of another file. The core mechanism required by #2.
Hence after due consideration we are planning to execute
the 4 sub topics in the following order:
1. defragmenting free space.
2. enhanced/faster filesystem scanning.
3. ability to defragment only portions of files rather
than just whole files.
4. explicit control of locality for groups of files.
Comments regarding the same will be appreciated. We would also like to thankÂ
Dave for his inputs. We look forward to working with the community and hope to
make a valuable contribution.
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