ok
hadn't seen this one when I sent the previous email..
Julian
On Mon, 28 Jun 1999, Matthew Dillon wrote:
> :You are right that the buffer cache is very tricky. It is hard to
> :change it in ways that preserves functionality and performance.
> :The port of my buffer locking code from BSD/OS has caused problems
> :largely because of a different buffer cache implementation and
> :especially SMP models between the two systems (BSD/OS has no spl's
> :for example). However, this is not a half baked idea that I have
> :come up with and thrown in without thinking. Recursive locking is
> :*required* to get stacking filesystems like union and loopback
> :working reliably. As they currently stand they are full of code to
> :try and track locks at layers all up and down the stack. This code
> :is really nasty and in many cases broken (leading to deadlocks or
> :crashes). The snapshot code also is most easily implemented with
> :recursive locking, the alternative being to put lock monitoring
> :all through bmap and block allocation code. So yes, it would be
> :wonderful if the world could be simple, and I am not a huge fan of
> :the complexity of the buffer locking code. But, I have considered
> :the alternatives and they are worse.
> :
> : Kirk
>
> Wow! Timeout! Miscommunication.
>
> I am talking strictly about struct buf locking. I understand and agree
> completely that recursive locking is absolutely necessary for the
> VFS layering!
>
> I am not throwing your work out - precisely the opposite, I want to keep
> your work pretty much as is except for two things: (1) I want to replace
> lockmgr locks ( and I don't mind implementing recursive exclusive locking
> in the replacement, though I would rather avoid it! ), and (2) I want to
> find a better way to implement the BUF_KERNPROC() stuff... basically I
> want to try to find a way to localize the necessary effect in one place
> in the code rather then have the BUF_KERNPROC() macros strewn all over the
> code. Same effect, slightly different code organization, that's all.
>
> There must be a choke point somewhere where we can put the code.
>
> -Matt
> Matthew Dillon
> <[EMAIL PROTECTED]>
>
>
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