[Devel] Re: [RFC] [-mm PATCH] Memory controller fix swap charging context in unuse_pte()

[Hugh Dickins]

On Tue, 30 Oct 2007, Balbir Singh wrote:
> 
> At this momemnt, I suspect one of two things
> 
> 1. Our mods to swap_state.c are different

I believe they're the same (just take swap_state.c back to how it
was without mem_cgroup mods) - or would be, if after finding this
effect I hadn't added a "swap_in_cg" switch to move between the
two behaviours to study it better (though I do need to remember
to swapoff and swapon between the two: sometimes I do forget).

> 2. Our configuration is different, main-memory to swap-size ratio

I doubt the swapsize is relevant: just so long as there's some (a
little more than 200M I guess); I've got 1GB-2GB on different boxes.

There may well be something about our configs that's significantly
different.  I'd failed to mention SMP (4 cpu), and that I happen
to have /proc/sys/vm/swappiness 100; but find it happens on UP
also, and when I go back to default swappiness 60.

I've reordered your mail for more dramatic effect...
> 
> On a real box - a powerpc machine that I have access to

I've tried on 3 Intel and 1 PowerPC now: the Intels show the OOMs
and the PowerPC does not.  I rather doubt it's an Intel versus
PowerPC issue as such, but interesting that we see the same.

> 
> 1. I don't see the OOM with the mods removed (I have swap
>    space at-least twice of RAM - with mem=512M, I have at-least
>    1G of swap).

mem=512M with 1G of swap, yes, I'm the same.

> 2. Running under the container is much much faster than running
>    swapout in the root container. The machine is almost unusable
>    if swapout is run under the root container

That's rather interesting, isn't it?  Probably irrelevant to the
OOM issue we're investigating, but worthy of investigation in itself.

Maybe I saw the same on the PowerPC: I simply forgot to set up the
cgroup one time, and my sequence of three swapouts (sometimes only
two out of three OOM, on those boxes that do OOM) seemed to take a
very long time (but I wasn't trying to do anything else on it at
the same time, so didn't notice if it was "unusable").

I'll probe on.

Hugh
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