Subject: Re: mfs woes
To: David Young <email@example.com>
From: Steven M. Bellovin <firstname.lastname@example.org>
Date: 07/14/2004 08:33:51
In message <20040714033948.GB13570@che.ojctech.com>, David Young writes:
>On Tue, Jul 13, 2004 at 11:17:20PM -0400, Steven M. Bellovin wrote:
>> In message <20040713230112.A426@noc.untraceable.net>, Andrew Brown writes:
>> >On Tue, Jul 13, 2004 at 05:18:31PM -0500, David Young wrote:
>> >>I am told that blocks in the memory filesystem (mfs) can end up in the
>> >>buffer cache: this double-whammy on memory can lead to memory exhaustion.
>> >yes, 'cause it's a "file system".
>> >>The problem is compounded (I do not understand how or why) when multiple
>> >>mfs are in use.
>> >>Is there any bug-fix or work-around for the memory-inefficiency/exhaustion
>> >>issue? Can somebody outline what a fix would look like?
>> >write a real swap-based file system? mfs also comes with a ~2.9
>> >gigabyte limit (on i386, at least). when using USE_TOPDOWN_VM. when
>> >you're not, it comes with a ~1.8 gigabyte limit. regardless of how
>> >much ram or swap you have.
>> Given the new buffer cache architecture, I've been wondering if mfs
>> even makes sense these days. Perhaps a disk partition mounted with
>> async would provide comparable performance? I don't know; I haven't
>> tried it. But I'm getting ready to bring up a new machine; I might
>> reserve a partition and see what happens.
>I think that an in-memory filesystem makes the most sense for my
>applicatoin: I am using either a CompactFlash card or a CD-ROM as the
>"hard drive." I do not want to keep volatile information on the former;
>I cannot keep it on the latter.
You and Andrew make good points about special cases. I should amend my
suggestion: does MFS make sense for /tmp on ordinary machines?
--Steve Bellovin, http://www.research.att.com/~smb