Re: OOM fixes 2/5

From: Andrea Arcangeli
Date: Fri Jan 21 2005 - 01:37:43 EST


On Thu, Jan 20, 2005 at 10:20:56PM -0800, Andrew Morton wrote:
> Andrea Arcangeli <andrea@xxxxxxx> wrote:
> >
> > This is the forward port to 2.6 of the lowmem_reserved algorithm I
> > invented in 2.4.1*, merged in 2.4.2x already and needed to fix workloads
> > like google (especially without swap) on x86 with >1G of ram, but it's
> > needed in all sort of workloads with lots of ram on x86, it's also
> > needed on x86-64 for dma allocations. This brings 2.6 in sync with
> > latest 2.4.2x.
>
> But this patch doesn't change anything at all in the page allocation path
> apart from renaming lots of things, does it?

In the allocation path not, but it rewrites the setting algorithm, so
from somebody watching it from userspace it's a completely different
thing, usable for the first time ever in 2.6. Otherwise userspace would
be required to have knowledge about the kernel internals to be able to
set it to a sane value. Plus the new init code is much cleaner too.

> AFAICT all it does is to change the default values in the protection map.
> It does it via a simplification, which is nice, but I can't see how it
> fixes anything.

Having this patch applied is a major fix. See again the google fix
thread in 2.4.1x. 2.6 is vulnerable to it again. This patch makes the
feature usable and enables the feature as well, which is definitely a
fix as far as an end user is concerned (google was the user in this case).
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