Block size limited to Linux page size?

Block size limited to Linux page size?

[Thomas King]

To fill in one piece of information, I'm reading the maximum block size can be
limited by the Linux page size, 4K on x86. Is this true in btrfs?

Thanks!
Tom King

Block size limited to Linux page size?

[Thomas King]

To fill in one piece of information, I'm reading the maximum block size can be
limited by the Linux page size, 4K on x86. Is this true in ext4?

I know this is a basic question, so thanks for humoring me.
Tom King

Re: Block size limited to Linux page size?

[Eric Sandeen]

Thomas King wrote:
> To fill in one piece of information, I'm reading the maximum block size can be
> limited by the Linux page size, 4K on x86. Is this true in ext4?
> 
> I know this is a basic question, so thanks for humoring me.
> Tom King

Generally, yes.

There are patches:

ftp://ftp.kernel.org/pub/linux/kernel/people/christoph/largeblocksize/4/patches/

but I'm not sure what the current state of all that is, honestly...

Before it's discussed as a limitation though it'd be interesting to see
some recent benchmarks on how much it might actually matter.

>From some reports:
http://kerneltrap.org/Linux/Large_Blocksize_Performance

it may indeed help.

-Eric

Re: Block size limited to Linux page size?

[Chris Mason]

On Tue, Jun 03, 2008 at 11:57:54AM -0500, Thomas King wrote:
> To fill in one piece of information, I'm reading the maximum block size can be
> limited by the Linux page size, 4K on x86. Is this true in btrfs?

The kernel code supports much larger block sizes for metadata, but there
is a current limitation that the checksum error handling code may have
some races on larger block sizes.

So, the default is the same as the page size, but larger sizes will soon
work again (once better btree locking code is in place).

-chris