Re: [PATCH] Btrfs: set default max_inline to 8KiB instead of 8MiB

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On Fri, Aug 09, 2013 at 01:47:24PM +0800, Miao Xie wrote:
> On thu, 8 Aug 2013 22:45:48 +0100, Filipe David Borba Manana wrote:
> > 8MiB is way too large and likely set by mistake. This is not
> > a significant issue as in practice the max amount of data
> > added to an inline extent is also limited by the page cache
> > and btree leaf sizes.
> 
> I don't think 8KB is a reasonable value of the default max inline size
> because it makes no sense on the machine whose page size is 4KB.

Page size limit is artificial implied by the implementation and on a 4k
page machine max_inline does not take place. Even if it's 4k, it does
not apply because the leaf space is smaller.

> I think 4KB is a reasonable value, because we may mount the fs on
> the machines with the different page size in the future, in order to
> avoid the compatible problem, we should use the min page size as
> the max inline size.

If there's support for mounting a fs with sectorsize != pagesize, this
will work automatically. Currently such filesystem fails to mount, as we
know.

Whether it's 4k or 8k could be decided by the performance impact, but I
have no numbers to vote for either.

david
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