Date: Wed, 05 Apr 1995 04:01:43 -0700 From: David Greenman <davidg@Root.COM> To: Bruce Evans <bde@zeta.org.au> Cc: hackers@FreeBSD.org Subject: Re: swap always use at least 64KB ? Message-ID: <199504051101.EAA00175@corbin.Root.COM> In-Reply-To: Your message of "Wed, 05 Apr 95 20:52:05 %2B1000." <199504051052.UAA16461@godzilla.zeta.org.au>
next in thread | previous in thread | raw e-mail | index | archive | help
>>>which is kind of curious, as the machine has 16 MB ram and almost >>>no activity going on... Swap partition, when in use, are always >>>reported with at least 64 KB in use. >>> >>>Is there any explaination ? > >> The first swap block is always pre-allocated. This was done to work around >>a problem with people putting their swap partition at the beginning of their >>disk (the system would happily try to destroy the label). I suppose it would >>be better to change swapinfo/pstat to not include the first block of swap >>space in its report. > >There must be bugs in the write protection of the label for that to happen. > >The diskslice "driver" snoops on writes to label sector(s) and rejects >writing of invalid labels even when write protection is off. > >Similar snooping is required for protecting the MBR and secondary BR's. There were two manifestations. It would either destroy your label (I think this was in the SCSI case) or it would get EROFS when the swap pager tried to page something out to it. I think the 'destroy your label' problem was fixed awhile ago. Now the pager just fails with the EROFS. ...Anyway, the first chunk can't be used. -DG
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?199504051101.EAA00175>