Date: Fri, 13 Feb 2004 20:47:54 -0500 (EST) From: Robert Watson <rwatson@freebsd.org> To: Colin Percival <colin.percival@wadham.ox.ac.uk> Cc: FreeBSD Hackers <FreeBSD-Hackers@freebsd.org> Subject: Re: malloc backed md/mfs filesystem swapped? Message-ID: <Pine.NEB.3.96L.1040213204656.29948H-100000@fledge.watson.org> In-Reply-To: <6.0.1.1.1.20040214014043.040c9d40@imap.sfu.ca>
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On Sat, 14 Feb 2004, Colin Percival wrote: > At 00:56 14/02/2004, Robert Watson wrote: > >If you > >have swap available, you pretty much always want to use swap-backing for > >memory disks -- if there's room in memory they will run as fast as > >malloc-backed, but you don't have to be as worried about the "Oh shoot, > >I'm out of room" case. > > Actually, there is one consideration: swap-backed memory disks have a > sector size equal to the machine page size. This will result in some > inflation in memory usage, and can confuse program which expect a sector > size of 512 bytes (for example, dd, which I plan on fixing but I haven't > gotten around to yet). One such application is Vinum, actually, which does not like using swap-backed storage nodes, although maybe I fixed that. Robert N M Watson FreeBSD Core Team, TrustedBSD Projects robert@fledge.watson.org Senior Research Scientist, McAfee Research
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