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Re: [dm-devel] [PATCH] Latest dm-userspace, with memory reclaim



From: FUJITA Tomonori <fujita tomonori lab ntt co jp>
Subject: Re: [dm-devel] [PATCH] Latest dm-userspace, with memory reclaim
Date: Sun, 10 Sep 2006 22:34:39 +0900

> From: Dan Smith <danms us ibm com>
> Subject: [dm-devel] [PATCH] Latest dm-userspace, with memory reclaim
> Date: Tue, 29 Aug 2006 09:54:38 -0700
> 
> > This is the latest version of dm-userspace.  I have added a
> > (configurable) limit on the number of remap objects the kernel will
> > maintain in memory before re-using old ones.
> > 
> > I think it may be beneficial to have a soft and a hard limit on this,
> > to allow allocation to be done if no remaps can be re-used at a given
> > point (up to the hard limit).  Comments appreciated.
> 
> How about removing the remap object mechanism?
> 
> You said that the remap object mechanism improves the performance by
> avoiding contacting user space for every requests. However, as you
> see, Xen blktap (contacting user space for every requests) and blkback
> (doing I/O in kernel) performances are comparable. dm-userspace's poor
> performance of user space access is due to ioctl, an inefficient
> interface. The blktap uses shared ring buffer between kernel and user
> space, which enables us to batch multiple requests without data
> copies.
> 
> Here's a patch to remove the remap object mechanism and add replaced
> ioctl with ring buffer.

The mailing list removed my patch for some reasons. So I uploaded the
patch too:

http://www.kernel.org/pub/linux/kernel/people/tomo/dmu/ringbuf.patch


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