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Subject[ANNOUNCE] Btrfs v0.12 released
Date
Hello everyone,

I wasn't planning on releasing v0.12 yet, and it was supposed to have some
initial support for multiple devices. But, I have made a number of
performance fixes and small bug fixes, and I wanted to get them out there
before the (destabilizing) work on multiple-devices took over.

So, here's v0.12. It comes with a shiny new disk format (sorry), but the gain
is dramatically better random writes to existing files. In testing here, the
random write phase of tiobench went from 1MB/s to 30MB/s. The fix was to
change the way back references for file extents were hashed.

Other changes:

Insert and delete multiple items at once in the btree where possible. Back
references added more tree balances, and it showed up in a few benchmarks.
With v0.12, backrefs have no real impact on performance.

Optimize bio end_io routines. Btrfs was spending way too much CPU time in the
bio end_io routines, leading to lock contention and other problems.

Optimize read ahead during transaction commit. The old code was trying to
read far too much at once, which made the end_io problems really stand out.

mount -o ssd option, which clusters file data writes together regardless of
the directory the files belong to. There are a number of other performance
tweaks for SSD, aimed at clustering metadata and data writes to better take
advantage of the hardware.

mount -o max_inline=size option, to override the default max inline file data
size (default is 8k). Any value up to the leaf size is allowed (default
16k).

Simple -ENOSPC handling. Emphasis on simple, but it prevents accidentally
filling the disk most of the time. With enough threads/procs banging on
things, you can still easily crash the box.

-chris


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