Re: OOM fixes 2/5

[Andrea Arcangeli]

On Fri, Jan 21, 2005 at 05:36:14PM +1100, Nick Piggin wrote:
> I think it should be turned on by default. I can't recall what

I think it too, since the number of people that can be bitten by this is
certainly higher than the number of people who knows the VM internals
and for what kind of workloads they need to enable this by hand to avoid
risking lockups (notably with boxes without swap or with heavy pagetable
allocations all the time which is not uncommon with db usage).

This is needed on x86-64 too to avoid pagetables to lockup the dma zone.
Or anyways it's needed also on x86 for the dma zone on <1G boxes too.

Anyway if you leave it off by default I don't mind, with my new code
forward ported stright from 2.4 mainline, it's possible for the first
time to set it from userspace without having to embed knowledge on the
kernel min_kbytes settings at boot time. So if you want it down by
default it simply means we'll guarantee it on our distro with userland.
Setting a sysctl at boot time is no big deal for us (of course leaving
it enabled by default in kernel space is older distro where userland
isn't yet aware about it). So it's pretty much up to you, as long as we
can easily fixup in userland is fine with me and I already tried a dozen
times to push mainline in what I believe to be the right direction (like
I already did in 2.4 mainline since that same code is enabled by default
in 2.4).

The sysctl name had to change to lowmem_reserve_ratio because its
semantics are completely different now.
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