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akiradeveloper / dm-writeboost

Log-structured Caching for Linux
GNU General Public License v2.0
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May not accept 0 as the offset? #183

Open akiradeveloper opened 7 years ago

akiradeveloper commented 7 years ago

This is what came up with when reading the code.

In this example of initialization dmsetup create wbdev --table "0 $sz writeboost $BACKING $CACHE 2 writeback_threshold 70", the number 0 after the word table is called offset. It should be able to accept number other than 0.

But the current Writeboost may only accept 0. I think all users now set the number to 0. Waiting for user report.

akiradeveloper commented 7 years ago

The test in writeboost-test-suite uses 0 as the offset. s"0 ${backingDev.bdev.size} writeboost ${backingDev.bdev.path} ${cacheDev.bdev.path}" + optionalArgs but to change this number will cause wide range of changes in other codebase. I don't think it's worthy.

akiradeveloper commented 7 years ago

The motivation to use offset other than 0 is creating a large virtual device that is concatenating multiple virtual devices or mappings. When implementing linear target, it sounds essential but for caching target it doesn't for me. As a fact, dm-cache target seems to be ignoring this because it doesn't use dm_target_offset function in it.