Re: [PATCH 00/18] multiple preferred nodes

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On 20-06-24 22:07:50, Michal Hocko wrote:
> On Wed 24-06-20 13:01:40, Ben Widawsky wrote:
> > On 20-06-24 21:51:58, Michal Hocko wrote:
> > > On Wed 24-06-20 12:37:33, Ben Widawsky wrote:
> > > > On 20-06-24 20:39:17, Michal Hocko wrote:
> > > > > On Wed 24-06-20 09:16:43, Ben Widawsky wrote:
> [...]
> > > > > > > Or do I miss something that really requires more involved approach like
> > > > > > > building custom zonelists and other larger changes to the allocator?
> > > > > > 
> > > > > > I think I'm missing how this allows selecting from multiple preferred nodes. In
> > > > > > this case when you try to get the page from the freelist, you'll get the
> > > > > > zonelist of the preferred node, and when you actually scan through on page
> > > > > > allocation, you have no way to filter out the non-preferred nodes. I think the
> > > > > > plumbing of multiple nodes has to go all the way through
> > > > > > __alloc_pages_nodemask(). But it's possible I've missed the point.
> > > > > 
> > > > > policy_nodemask() will provide the nodemask which will be used as a
> > > > > filter on the policy_node.
> > > > 
> > > > Ah, gotcha. Enabling independent masks seemed useful. Some bad decisions got me
> > > > to that point. UAPI cannot get independent masks, and callers of these functions
> > > > don't yet use them.
> > > > 
> > > > So let me ask before I actually type it up and find it's much much simpler, is
> > > > there not some perceived benefit to having both masks being independent?
> > > 
> > > I am not sure I follow. Which two masks do you have in mind? zonelist
> > > and user provided nodemask?
> > 
> > Internally, a nodemask_t for preferred node, and a nodemask_t for bound nodes.
> 
> Each mask is a local to its policy object.

I mean for __alloc_pages_nodemask as an internal API. That is irrespective of
policy. Policy decisions are all made beforehand. The question from a few mails
ago was whether there is any use in keeping that change to
__alloc_pages_nodemask accepting two nodemasks.




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