Re: [PATCH] mm, meminit: Serially initialise deferred memory if trace_buf_size is specified

[Andrew Morton]

On Fri, 17 Nov 2017 13:19:56 -0500 Pavel Tatashin <pasha.tatashin@xxxxxxxxxx> wrote:

> On Thu, Nov 16, 2017 at 5:06 AM, Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx> wrote:
> > 4. Put a check into the page allocator slowpath that triggers serialised
> >    init if the system is booting and an allocation is about to fail. It
> >    would be such a cold path that it would never be noticable although it
> >    would leave dead code in the kernel image once boot had completed
> 
> Hi Mel,
> 
> The forth approach is the best as it is seamless for admins and
> engineers, it will also work on any system configuration with any
> parameters without any special involvement.

Apart from what-mel-said, I'd be concerned that this failsafe would
almost never get tested.  We should find some way to ensure that this
code gets exercised in some people's kernels on a permanent basis and
I'm not sure how to do that.

One option might be to ask Fengguang to add the occasional
test_pavels_stuff=1 to the kernel boot commandline.  That's better
than nothing but 0-day only runs on a small number of machine types.