Date: Tue, 06 Nov 2007 06:34:06 +0000 From: James Mansion <james@mansionfamily.plus.com> To: freebsd-scsi@freebsd.org, tom@samplonius.org Subject: iSCSI in 7.0 Message-ID: <47300ADE.5070506@mansionfamily.plus.com>
next in thread | raw e-mail | index | archive | help
(Apologies for the bad quoting: I had to copy the response from a web view of the archive since I don't seem to have received anything except the 'Current problems' mail. Weird.) Tom Samplonius wrote: >Well, since it is a kernel mode driver, it has to be use kernel memory. Yes, but ... >There should be no issue with a swap deadlock, because the iSCSI client >can't get more memory until some memory is swapped in. But FreeBSD >does not generally like running out kernel memory either. That does not *necessarily* follow, which is the crux of my question. Most kernels will have a pool for non-pageable memory and allocate from a pageable pool too, even though the memory is 'kernel memory' and not addressable from any user context. FreeBSD can run with a very lean kernel footprint (which is the reason for my interest) and yet support C10k systems with kqueue without static reconfiguration of the kernel, and its hard to see how this could possibly be the case with a fully static allocation. In many cases thread stacks, socket send and receive buffers, pipe buffers etc *will* be pageable. That's the case for the buffers used to receive and process IP datagrams in Linux I believe. > I think Linux is using a kernel mode driver too. Well, there were several iSCSI clients > when I checked. I'm not sure which you are looking at. I think your reasoning is flawed here, for the same reason. Now, it may be that FreeBSD does have a lot more non-pageable allocation and is able to reassemble incoming IP packets and process iSCSI data without any allocation from pageable memory. I believe its not normally a trivial problem unless you are prepared to perform an extra copy operation. Do you know this for a fact? > AoE sounds completely retarded. I hope it disappears before people think it is actually something serious. Well, that's simply opinion. It is certainly a simplified approach, but I think to suggest that it is entirely without merit is bogus. And I have discussed the issue with Linux IP memory management and swap support with the Coraid developer - its a known 'issue' (or non-issue for Linus it seems: its only swap rather than net boot that's affected after all, and most blades do come with disks). James
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?47300ADE.5070506>