Messages in this thread | | | From | Miklos Szeredi <> | Subject | Re: [patch 1/2] fuse: delete dead .write_begin and .write_end aops | Date | Wed, 10 Aug 2011 13:24:36 +0200 |
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Christoph Hellwig <hch@infradead.org> writes:
> On Mon, Aug 08, 2011 at 05:05:20PM +0200, Miklos Szeredi wrote: >> > The loop code still calls them uncondtionally. This actually is a big >> > as write_begin and write_end require filesystems specific locking, >> > and might require code in the filesystem to e.g. update the ctime >> > properly. I'll let Miklos chime in if leaving them in was intentional, >> > and if it was a comment is probably justified. >> >> Loop checks for ->write_begin() and falls back to ->write if the former >> isn't defined. >> >> So I think the patch is fine. I tested loop over fuse, and it still >> works after the patch. > > It works, but it involves another data copy, which will slow down > various workloads that people at least historically cared about.
AFAICS, normally there isn't an additional copy. If ->write_begin is defined the copy from the bio_vec to the filesystem page is done with transfer_none() in the loop driver.
Otherwise the copy is done by ->write() itself on the kmapped bio.
If there's a crypto transfer function then a temporary page will be used in the no write_begin case. But I don't think there the additional copy makes much difference or that anyone cares.
Thanks, Miklos
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