preallocate CPU usage - pre4

Jamie Lokier jamie at
Mon Nov 19 05:06:04 GMT 2007

Matt McCutchen wrote:
> I notice that the Linux kernel 2.6.23 has gained a system call
> "fallocate" that preallocates at the filesystem level like Cygwin's
> implementation of posix_fallocate; thus, preallocation may become (at
> least slightly) helpful on Linux.  Unfortunately, neither ext2 nor
> reiserfs supports this call yet, at least in the kernel on my computer;
> I hope support will be added soon.

It won't work on EXT2 because it requires changes to the filesystem
format, to reserve space without writing data.

So, you can use it with EXT4 instead...  I think you can change EXT2/3
to EXT4 without reformatting, just like EXT2 to EXT3.

In Linux 2.6.23, fallocate works on EXT4 and OCFS2 filesystems.
Support is expected on CIFS eventually.

-- Jamie

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