Messages in this thread | | | Date | Sun, 7 Mar 2004 09:41:20 +0100 | From | Ingo Molnar <> | Subject | Re: 2.4.23aa2 (bugfixes and important VM improvements for the high end) |
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* Andrea Arcangeli <andrea@suse.de> wrote:
> [...] but I'm quite confortable to say that up to 16G (included) 4:4 > is worthless unless you've to deal with the rmap waste IMHO. [...]
i've seen workloads on 8G RAM systems that easily filled up the ~800 MB lowmem zone. (it had to do with many files and having them as a big dentry cache, so yes, it's unfixable unless you start putting inodes into highmem which is crazy. And yes, performance broke down unless most of the dentries/inodes were cached in lowmem.)
as i said - it all depends on the workload, and users are amazingly creative at finding all sorts of workloads. Whether 4:4 or 3:1 is thus workload dependent.
should lowmem footprint be reduced? By all means yes, but only as long as it doesnt jeopardize the real 64-bit platforms. Is 3:1 adequate as a generic x86 kernel for absolutely everything up to and including 16 GB? Strong no. [not to mention that 'up to 16 GB' is an artificial thing created by us which wont satisfy an IHV that has a hw line with RAM up to 32 or 64 GB. It doesnt matter that 90% of the customers wont have that much RAM, it's a basic "can it scale to that much RAM" question.]
so i think the right answer is to have 4:4 around to cover the bases - and those users who have workloads that will run fine on 3:1 should run 3:1.
(not to mention the range of users who need 4GB _userspace_.)
but i'm quite strongly convinced that 'getting rid' of the 'pte chain overhead' in favor of questionable lowmem space gains for a dying (high-end server) platform is very shortsighted. [getting rid of them for purposes of the 64-bit platforms could be OK, but the argumentation isnt that strong there i think.]
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