Re: MPOL_BIND on memory only nodes
From: Michal Hocko
Date: Thu Oct 13 2016 - 08:52:29 EST
On Thu 13-10-16 16:28:27, Anshuman Khandual wrote:
> On 10/13/2016 03:37 PM, Michal Hocko wrote:
> > On Thu 13-10-16 15:24:54, Anshuman Khandual wrote:
> > [...]
> >> Which makes the function look like this. Even with these changes, MPOL_BIND is
> >> still going to pick up the local node's zonelist instead of the first node in
> >> policy->v.nodes nodemask. It completely ignores policy->v.nodes which it should
> >> not.
> > Not really. I have tried to explain earlier. We do not ignore policy
> > nodemask. This one comes from policy_nodemask. We start with the local
> > node but fallback to some of the nodes from the nodemask defined by the
> > policy.
> Yeah saw your response but did not get that exactly. We dont ignore
> policy nodemask while memory allocation, correct. But my point was
> we are ignoring policy nodemask while selecting zonelist which will
> be used during page allocation. Though the zone contents of both the
> zonelists are likely to be same, would not it be better to get the
> zone list from the nodemask as well ?
Why. Zonelist from the current node should contain all availanle zones
and get_page_from_freelist then filters this zonelist accoring to
mempolicy and nodemask
> Or I am still missing something
> here. The following change is what I am trying to propose.
> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> index ad1c96a..f60ab80 100644
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -1685,14 +1685,7 @@ static struct zonelist *policy_zonelist(gfp_t gfp, struct mempolicy *policy,
> nd = policy->v.preferred_node;
> case MPOL_BIND:
> - /*
> - * Normally, MPOL_BIND allocations are node-local within the
> - * allowed nodemask. However, if __GFP_THISNODE is set and the
> - * current node isn't part of the mask, we use the zonelist for
> - * the first node in the mask instead.
> - */
> - if (unlikely(gfp & __GFP_THISNODE) &&
> - unlikely(!node_isset(nd, policy->v.nodes)))
> + if (unlikely(!node_isset(nd, policy->v.nodes)))
> nd = first_node(policy->v.nodes);
That shouldn't make much difference as per above.