Messages in this thread | | | Date | Tue, 29 Mar 2016 10:09:21 +0200 | From | Lars Ellenberg <> | Subject | Re: [PATCH 7/8] block: drbd: avoid to use BIO_MAX_SIZE |
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On Tue, Mar 29, 2016 at 12:31:24AM -0700, Christoph Hellwig wrote: > On Tue, Mar 22, 2016 at 02:12:28PM +0800, Ming Lei wrote: > > drbd is the only user of BIO_MAX_SIZE, so use BIO_MAX_PAGES > > instead. > > That whole code block looks completely bogus to me, although your patch > doesn't make it any worse. > > I/O size for a network protocol shouldn't dependend on the number of > vectors in a kernel internal structure.
That's correct. But we needed some limit there. Initially, up until I changed it like six years ago iirc, the receiving side would receive into a single bio. So limiting us to what a single bio could usually handle seemed like a good idea at the time.
Today, we should be able to handle 128 MiB easily, maybe more. But that would require a protocol bump to stay backwards compatible.
The part about "architecture not supported", if our limit (1 MiB) is bigger than the "system" limit: Never met that in real life. Probably not even possible. Just a paranoia on my side: what if. If that would have happened somewhere, on some strange architecture or configuration, I wanted to know about that. Best way: don't even compile.
> Well, getting rid of BIO_MAX_SIZE is worth it, so: > > Reviewed-by: Christoph Hellwig <hch@lst.de>
Thanks,
Lars Ellenberg
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