kernel memory checks on boot vs. boot time

Alexander Best arundel at
Wed Mar 23 23:29:26 UTC 2011

On Thu Mar 24 11, Andriy Gapon wrote:
> on 23/03/2011 21:28 Peter Wemm said the following:
> > Part of the reason for this "check" is a sanity check to make sure we
> > enumerated memory correctly and that we have at least got basic ram
> > functionality.  The existence of hw.physmem complicates this.  On
> > machines where hw.physmem could be used to tell the kernel that there
> > was more ram present than the kernel enumerates (old bioses etc), this
> > was kind of important to sanity check.
> > 
> > Even though modern hardware will fail windows compliance tests if the
> > SMAP etc is wrong, never underestimate the ability of bios makers to
> > find new and bizarre ways of screwing things up.
> > 
> > I'd kinda like to keep a basic "is this real, non mirrored ram?" test
> > there.  eg: the 2-pass step of writing physical address into each page
> > and then checking that they are still there on the second pass.
> > 
> > Oh, did I mention the machine where the ACPI bios info tells the OS
> > that the current state is S3 (suspended to ram) instead of S0?
> > 
> > When the kernel blows up at boot without a message.. we get the blame,
> > not the bios maker.
> I hear what you are saying, but is there any other OS that takes this level of
> responsibility?  Should we either?
> I mean, hardware and BIOS vendors can screw up things in very creative ways and
> it's impossible to protect against that.  When we are bug-compatible with some
> other OS, then it's one thing; but when we try to to be even "better" than that,
> that's quite another thing.

to be honest, i suspect 99.99999999...% of RAM issues users are experiencing
are issues not being detected by the current ram checks in place. these
included defects or wrong bios setting (overclocking, etc.).

that's why i think they are unnecessary. i kind of like how a few linux distros
come up with a boot menue which lets you run memtest. if you have any suspicion
that your RAM is causing issues: run memtest!

...after all: if users have the feeling the harddrive is causing problems: run
smartctl! nobody expects the OS to check whether the harddrives are ok. that's
what smartd is designed for.

> -- 
> Andriy Gapon


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