nilfs2: add mount option that reduces super block writes
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| # | Subject and files | Size | Replies | Applied |
|---|---|---|---|---|
| 1/1 | nilfs2: add mount option that reduces super block writesfs/ fs/ fs/ +4 more | +281 | 7 replies |
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Cover letter [PATCH v2 0/1] nilfs2: add mount option that reduces super block writes
Hi,
This is an experimental patch. I am not suggesting to use this as a default recovery option. I had some time over the weekend to improve my first version significantly. The primary goal of this patch is to test how bad a linear scan of all segments really is for performance.
The patch introduces a mount option that allows the user to disable the periodic overwrite of the super block during normal file system operation. The super block needs to point to the latest segment, to allow the file system to recover in case of an unclean shutdown, but this leads to a lot of writes to this one particular block. This is usually not a problem, but it can lead to wear leveling problems with cheap flash based storage devices.
Instead of periodically writing to the super block, this patch only writes at mount and umount time and performs a linear scan for the latest segment in case a recovery is necessary.
Here are the test results for some devices:
100GB HDD:
Recovery: 45.042s Normal Mount: 0.165s
100GB SSD:
Recovery: 0.752s Normal Mount: 0.059s
16GB SD-Card:
Recovery: 3.833s Normal Mount: 0.652s
16GB Micro-SD-Card:
Recovery: 4.011s Normal Mount: 1.104s
8GB USB-Stick:
Recovery: 1.704s Normal Mount: 0.549s
The HDD is obviously intolerably slow for this task, but still the read ahead improved its time significantly.
SSDs are really really good for these kind of random read operations. I measured it three times to be sure. Since I know the addresses of the blocks in advance, I do a 64 block read ahead so that the I/O queue of the SSD is always full. That way it can read with almost full bandwidth.
The SD-Cards and the USB-Stick are not particularly fast, but they are small enough so that the recovery time is tolerable.
Best regards,
Andreas Rohner
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v2: Add validity checks
Add history of recent segments
Add check of partial segments
Add readahead
Add fast crc checksum replacing ss_pad
Andreas Rohner (1):
nilfs2: add mount option that reduces super block writes
fs/nilfs2/recovery.c | 248 ++++++++++++++++++++++++++++++++++++++++++++++ fs/nilfs2/segbuf.c | 16 ++- fs/nilfs2/segment.c | 3 +- fs/nilfs2/segment.h | 1 + fs/nilfs2/super.c | 10 +- fs/nilfs2/the_nilfs.c | 3 + include/linux/nilfs2_fs.h | 6 +- 7 files changed, 281 insertions(+), 6 deletions(-)
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