Re: [00/17] Large Blocksize Support V3

Eric W. Biederman
2007-05-04T13:35:51Z

Theodore Tso <tytso@mit.edu> writes:

> On Fri, Apr 27, 2007 at 01:48:49AM -0700, Andrew Morton wrote:
>> And other filesystems (ie: ext4) _might_ use it. But ext4 is extent-based,
>> so perhaps it's not work churning the on-disk format to get a bit of a
>> boost in the block allocator.
>
> Well, ext3 could definitely use it; there are people using 8k and 16k
> blocksizes on ia64 systems today. Those filesystems can't be mounted
> on x86 or x86_64 systems because our pagesize is 4k, though.
>
> And I imagine that ext4 might want to use a large blocksize too ---
> after all, XFS is extent based as well, and not _all_ of the
> advantages of using a larger blocksize are related to brain-damaged
> storage subsystems with short SG list support. Whether the advantages
> offset the internal fragmentation overhead or the complexity of adding
> fragments support is a different question, of course.
>
> So while the jury is out about how many other filesystems might use
> it, I suspect it's more than you might think. At the very least,
> there may be some IA64 users who might be trying to transition their
> way to x86_64, and have existing filesystems using a 8k or 16k
> block filesystems. :-)

How much of a problem would it be if those blocks were not necessarily
contiguous in RAM, but placed in normal 4K pages in the page cache?

I expect meta data operations would have to be modified but that otherwise
you would not care.

Eric