BTW, is the bigmem option incompatible with the nopentium command line
option? (It disables 4M pages)
FTR, the Athlon currently supports 16G. BIOSES for the Athlon...don't. I
don't know the K6 specs, but it was designed with PPro compatibility in
mind.
Nathan Zook
> -----Original Message-----
> From: Andrea Arcangeli [mailto:andrea@suse.de]
> Sent: Wednesday, February 02, 2000 7:58 PM
> To: Matt Chapman
> Cc: linux-kernel@vger.rutgers.edu
> Subject: Re: bigmem questions
>
>
> On Wed, 2 Feb 2000, Matt Chapman wrote:
>
> >I have a couple of questions about the BIGMEM implementation.
> >
> >I understand BIGMEM will support up to 64G of physical RAM, but I
> >haven't been able to glean from the postings what a user-process'
> >virtual address space will be. [..]
>
> User-process virtual memory is physically limited to 4giga in the IA32
> architecture (unless you want to play dirty with segmentation
> at least...
> and you probably prefer to more cleanly use shm memory and attach and
> deattach to shm segments or doing similar userspace non-IA32 specific
> tricks to access the whole RAM). New PAE stuff won't help you on the
> virtual memory side.
>
> Today you can use alpha with 2.2.14+bigmem patch if you need more RAM
> per-task (is 2T enough for you? :).
>
> Due the kernel/user split on the virtual memory the usual limit for
> linux-IA32 is around 2giga per-task (there are two one liner on my
> ftp-area to increase it to 3.5g per-task though).
>
> >[..] The SGI and SuSE patches that I've
> >seen map almost 4G virtual into physical RAM. Does BIGMEM support
> >this range or will it retain the old 3G virtual space?
>
> NOTE: when you talk about the SuSE patches you are exactly
> talking about
> BIGMEM. FYI: BIGMEM is been originally designed and developed
> from scratch
> by me at SuSE and Gerhard Wichert at Siemens.
>
> The BIGMEM SuSE patches that broken the 2giga RAM limit on
> IA32 are been
> included into 2.3.16. Then during 2.3.x the patch that did
> the rest of the
> stuff necessary for >4g support (so implementing the three level
> pagetables of PAE mode and changing GFP to return a struct
> page * instead
> of a 32bit interger) also renamed the word "bigmem" to "highmem".
>
> (BTW, personally I prefer the original "bigmem" name for the
> thing, and
> the rename just generated confusion to you for example.)
>
> >Does BIGMEM adjust to the amount of RAM installed? For example, the
> >2.2.x release requires one kernel build for less than 1G and another
> >for over 1G. Will BIGMEM support say 16M to 64G with the same kernel
> >build?
>
> You can support more than 4giga only on P6 chips, a kernel
> compiled for
> supporting 64giga of ram won't run on older IA32 chips like the P5
> generation, I actually don't know about AMD and others.
> Probably we should
> put a dependency for PAE mode on P6 compile.
>
> If you compile without PAE (so with 4G support) the resulting
> kernel will
> run all over the place.
>
> >How about support for 16M to 4G RAM with one kernel?
>
> Fine. You can just do it with 2.2.14+bigmem btw.
>
> >If rebuilding is required, why? [..]
>
> Not required.
>
> > [..] Is there a sizable performance hit in
> >making it dynamic?
>
> No.
>
> Andrea
>
>
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