On Fri, Jun 30, 2006 at 10:13:06AM -0700, Badari Pulavarty wrote:
> I tried adding "delayed allocation" for ext3 earlier. Yes. VFS level
> infrastructure would be nice. But, I haven't found much that we can
> do at VFS - which is common across all the filesystems (except
> mpage_writepage(s) handling). Most of the stuff is specific to
> filesystem implementation (even though it could be common) - coming
> out with VFS level interfaces to suite all the different filesystem
> delalloc would be *interesting* exercise.
Well, to be fair, I'm just going by what little I know about
XFS. They maintain a cache of all pages waiting on delayed allocation
for writepack. Why have this entire cache (hash, list, whatever) when
we could create some state on in the pagecache? We save a large chunk
of memory and some complex writeback code. I suspect you were thinking
of this when you said "mpage_writepage(s) handling". But this is a
large complexity win if we can do it.
The same with metadata/data ordering issues. ie, data=ordered
or even plain "creat(2); write(2)". I don't know how generic the
ordering is for each filesystem, but there is always room for play.
On-disk, of course each filesystem is going to be different.
I'm not sure we could fit a fully-generic aops->reserve_space() &
aops->commit_space() API. But I don't think we need to.
Joel
--
"Well-timed silence hath more eloquence than speech."
- Martin Fraquhar Tupper
Joel Becker
Principal Software Developer
Oracle
E-mail: [email protected]
Phone: (650) 506-8127
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