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mm, mempolicy: clean up __GFP_THISNODE confusion in policy_zonelist 

__GFP_THISNODE is documented to enforce the allocation to be satisified
from the requested node with no fallbacks or placement policy
enforcements.  policy_zonelist seemingly breaks this semantic if the
current policy is MPOL_MBIND and instead of taking the node it will
fallback to the first node in the mask if the requested one is not in
the mask.  This is confusing to say the least because it fact we
shouldn't ever go that path.  First tasks shouldn't be scheduled on CPUs
with nodes outside of their mempolicy binding.  And secondly
policy_zonelist is called only from 3 places:

 - huge_zonelist - never should do __GFP_THISNODE when going this path

 - alloc_pages_vma - which shouldn't depend on __GFP_THISNODE either

 - alloc_pages_current - which uses default_policy id __GFP_THISNODE is
   used

So we shouldn't even need to care about this possibility and can drop
the confusing code.  Let's keep a WARN_ON_ONCE in place to catch
potential users and fix them up properly (aka use a different allocation
function which ignores mempolicy).

[akpm@linux-foundation.org: coding-style fixes]
Link: http://lkml.kernel.org/r/20161013125958.32155-1-mhocko@kernel.org
Signed-off-by: Michal Hocko <mhocko@suse.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Mel Gorman <mgorman@suse.de>
Cc: David Rientjes <rientjes@google.com>
Cc: Anshuman Khandual <khandual@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Michal Hocko 2016-12-12 16:42:23 -08:00 committed by Linus Torvalds
parent fd60775aea
commit 6d8409580b
1 changed files with 8 additions and 16 deletions
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24
mm/mempolicy.c
View File

@ -1679,25 +1679,17 @@ static nodemask_t *policy_nodemask(gfp_t gfp, struct mempolicy *policy)
static struct zonelist *policy_zonelist(gfp_t gfp, struct mempolicy *policy, static struct zonelist *policy_zonelist(gfp_t gfp, struct mempolicy *policy,
int nd) int nd)
{ {
switch (policy->mode) { if (policy->mode == MPOL_PREFERRED && !(policy->flags & MPOL_F_LOCAL))
case MPOL_PREFERRED: nd = policy->v.preferred_node;
if (!(policy->flags & MPOL_F_LOCAL)) else {
nd = policy->v.preferred_node;
break;
case MPOL_BIND:
/* /*
* Normally, MPOL_BIND allocations are node-local within the * __GFP_THISNODE shouldn't even be used with the bind policy
* allowed nodemask. However, if __GFP_THISNODE is set and the * because we might easily break the expectation to stay on the
* current node isn't part of the mask, we use the zonelist for * requested node and not break the policy.
* the first node in the mask instead.
*/ */
if (unlikely(gfp & __GFP_THISNODE) && WARN_ON_ONCE(policy->mode == MPOL_BIND && (gfp & __GFP_THISNODE));
unlikely(!node_isset(nd, policy->v.nodes)))
nd = first_node(policy->v.nodes);
break;
default:
BUG();
} }
return node_zonelist(nd, gfp); return node_zonelist(nd, gfp);
} }