Re: mmotm 2015-01-22-15-04: qemu failure due to 'mm: memcontrol: remove unnecessary soft limit tree node test'

[Guenter Roeck]

On 01/23/2015 09:36 AM, Johannes Weiner wrote:
> On Fri, Jan 23, 2015 at 08:59:51AM -0800, Guenter Roeck wrote:
> > On 01/23/2015 08:02 AM, Johannes Weiner wrote:
> > > On Fri, Jan 23, 2015 at 09:17:44AM -0600, Christoph Lameter wrote:
> > > > On Fri, 23 Jan 2015, Johannes Weiner wrote:
> > > >
> > > > > Is the assumption of this patch wrong?  Does the specified node have
> > > > > to be online for the fallback to work?
> > > >
> > > > Nodes that are offline have no control structures allocated and thus
> > > > allocations will likely segfault when the address of the controls
> > > > structure for the node is accessed.
> > > >
> > > > If we wanted to prevent that then every allocation would have to add a
> > > > check to see if the nodes are online which would impact performance.
> > >
> > > Okay, that makes sense, thank you.
> > >
> > > Andrew, can you please drop this patch?
> > Problem is that there are three patches.
> >
> > 2537ffb mm: memcontrol: consolidate swap controller code
> > 2f9b346 mm: memcontrol: consolidate memory controller initialization
> > a40d0d2 mm: memcontrol: remove unnecessary soft limit tree node test
> >
> > Reverting (or dropping) a40d0d2 alone is not possible since it modifies
> > mem_cgroup_soft_limit_tree_init which is removed by 2f9b346.
>
> ("mm: memcontrol: consolidate swap controller code") gave me no issues
> when rebasing, but ("mm: memcontrol: consolidate memory controller
> initialization") needs updating.
>
> So how about this one to replace ("mm: memcontrol: remove unnecessary
> soft limit tree node test"):
>
> ---
> From: Johannes Weiner <hannes@xxxxxxxxxxx>
> Subject: [patch] mm: memcontrol: simplify soft limit tree init code
>
> - No need to test the node for N_MEMORY.  node_online() is enough for
>    node fallback to work in slab, use NUMA_NO_NODE for everything else.
>
> - Remove the BUG_ON() for allocation failure.  A NULL pointer crash is
>    just as descriptive, and the absent return value check is obvious.
>
> - Move local variables to the inner-most blocks.
>
> - Point to the tree structure after its initialized, not before, it's
>    just more logical that way.
>
> Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>

The latest version in mmotm passes my ppc64 qemu test, so it works
at least in this context.

Tested-by: Guenter Roeck <linux@xxxxxxxxxxxx>

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/