Subject: Re: 2.6.1-rc1-tiny2
From: Trond Myklebust <trond.myklebust@fys.uio.no>
To: Matt Mackall <mpm@selenic.com>
Cc: Mitchell Blank Jr <mitch@sfgoth.com>, Jens Axboe <axboe@suse.de>,
       linux-kernel <linux-kernel@vger.kernel.org>
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Date: Wed, 07 Jan 2004 16:41:38 -0500
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P? on , 07/01/2004 klokka 15:10, skreiv Matt Mackall:
> NFS is a good example of why the guarantees of mempool are being
> overstated - it still needs to allocate SKBs to make progress and
> preallocating a pool for other data structures can make that fail
> where it otherwise might not. The pool size for NFS (32) is also
> completely arbitrary as far as I can tell.

If you are in a hardware situation where you actually care about the
permanent size of that mempool, then you're barking up entirely the
wrong tree: there is a hell of a lot more memory to reclaim from not
having to build up all those nfs_page lists in the first place.

i.e. Rip out the entire asynchronous NFS read/write support, not just
the mempools.

As for the usefulness of the mempools in the situation where you have
asynchronous I/O: I agree that the socket layer screws any chance of a
guarantee. So does the server if it goes down, the network itself can
screw you,.... All in all, it is surprising how few guarantees NFS
offers you.
I therefore see the mempools as more of an optimization that mainly
avoid sleeping under a certain limited set of "reasonable"
circumstances.

Cheers,
  Trond
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