smbd: reporting of allocation size

Jeremy Allison jra at
Tue Jul 19 16:07:27 UTC 2016

On Tue, Jul 19, 2016 at 01:37:57PM +0300, Uri Simchoni wrote:
> 2. Anything is rounded up to "allocation roundup size" parameter that
> defaults to 1MB - I believe this rounding up was initially introduced in
> commit  22afba62c in 2001, then briefly removed and re-added in 2005,
> haven't found the relevant discussion in both cases, but it's supposed
> to be performance-related.
> For the "don't report zero allocation", I intend to refactor the code so
> that all the roundup is outside VFS, and remove this "don't report zero
> allocation" by default. Specific file systems will be able to overridet
> this (GPFS has its own VFS module anyway).
> For the roundup thing - I'd like to understand the source of this. How
> much we understood what was going on, and whether it's still required
> today. If it's not required, we may change the default or remove it
> completely.

Allocation roundup size actually was a performance win back
in the day (SMB1). Reporting it as larger (1MB) caused the
SMB1 client to issue larger read requests against Samba than
it did against a Windows server which reported the NTFS
allocation extent.

In the world of SMB2, not sure how much it's needed anymore.

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