On Mon 29-10-18 10:34:22, Dan Williams wrote:
On Mon, Oct 29, 2018 at 10:24 AM Michal Hocko
> On Mon 29-10-18 10:01:28, Alexander Duyck wrote:
> > On Mon, 2018-10-29 at 17:35 +0100, Michal Hocko wrote:
> > > You are already doing per-page initialization so I fail to see a larger
> > > unit to operate on.
> > I have a patch that makes it so that we can work at a pageblock level
> > since all of the variables with the exception of only the LRU and page
> > address fields can be precomputed. Doing that is one of the ways I was
> > able to reduce page init to 1/3 to 1/4 of the time it was taking
> > otherwise in the case of deferred page init.
> You still have to call set_page_links for each page. But let's assume we
> can do initialization per larger units. Nothing really prevent to hide
> that into constructor as well.
A constructor / indirect function call makes sense when there are
multiple sub-classes of object initialization, on the table I only see
3 cases: typical hotplug, base ZONE_DEVICE, ZONE_DEVICE + HMM. I think
we can look to move the HMM special casing out of line, then we're
down to 2. Even at 3 cases we're better off open-coding than a
constructor for such a low number of sub-cases to handle. I do not
foresee more cases arriving, so I struggle to see what the constructor
buys us in terms of code readability / maintainability?
I haven't dreamed of ZONE_DEVICE and HMM few years back. But anyway,
let me note that I am not in love with callbacks. I find them to be a
useful abstraction. I can be convinced (by numbers) that special casing
inside the core hotplug code is really beneficial. But let's do that at
a single place.
All I am arguing against throughout this thread is the
memmap_init_zone_device and the whole code duplication just because zone
device need something special.