Messages in this thread |  | | Date | Thu, 16 Apr 2015 10:26:35 -0700 | From | Andrew Morton <> | Subject | Re: [RFC PATCH 0/14] Parallel memory initialisation |
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On Thu, 16 Apr 2015 09:46:09 +0100 Mel Gorman <mgorman@suse.de> wrote:
> On Thu, Apr 16, 2015 at 12:25:01AM -0700, Andrew Morton wrote: > > On Mon, 13 Apr 2015 11:16:52 +0100 Mel Gorman <mgorman@suse.de> wrote: > > > > > Memory initialisation > > > > I wish we didn't call this "memory initialization". Because memory > > initialization is memset(), and that isn't what we're doing here. > > > > Installation? Bringup? > > > > It's about linking the struct pages to their physical page frame so > "Parallel struct page initialisation"?
Works for me.
> > I'd hoped the way we were > > going to do this was by bringing up a bit of memory to get booted up, > > then later on we just fake a bunch of memory hot-add operations. So > > the new code would be pretty small and quite high-level. > > That ends up being very complex but of a very different shape. We would > still have to prevent the sections being initialised similar to what this > series does already except the zone boundaries are lower. It's not as > simple as faking mem= because we want local memory on each node during > initialisation.
Why do "we want..."?
> Later after device_init when sysfs is setup we would then have to walk all > possible sections to discover pluggable memory and hot-add them. However, > when doing it, we would want to first discover what node that section is > local to and ideally skip over the ones that are not local to the thread > doing the work. This means all threads have to scan all sections instead > of this approach which can walk within its own PFN. It then adds pages > one at a time which is slow although obviously that part could be addressed. > > This would be harder to co-ordinate as kswapd is up and running before > the memory hot-add structures are finalised so it would need either a > semaphore or different threads to do the initialisation. The user-visible > impact is then that early in boot, the total amount of memory appears to > be rapidly increasing instead of this approach where the amount of free > memory is increasing. > > Conceptually it's straight forward but the details end up being a lot > more complex than this approach.
Could we do most of the think work in userspace, emit a bunch of low-level hotplug operations to the kernel?
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