mm/mempolicy: cleanup nodemask intersection check for oom

Patch series "mm/mempolicy: some fix and semantics cleanup", v4.

Current memory policy code has some confusing and ambiguous part about
MPOL_LOCAL policy, as it is handled as a faked MPOL_PREFERRED one, and
there are many places having to distinguish them.  Also the nodemask
intersection check needs cleanup to be more explicit for OOM use, and
handle MPOL_INTERLEAVE correctly.  This patchset cleans up these and
unifies the parameter sanity check for mbind() and set_mempolicy().

This patch (of 3):

mempolicy_nodemask_intersects seem to be a general purpose mempolicy
function.  In fact it is partially tailored for the OOM purpose
instead.  The oom proper is the only existing user so rename the
function to make that purpose explicit.

While at it drop the MPOL_INTERLEAVE as those allocations never has a
nodemask defined (see alloc_page_interleave) so this is a dead code and
a confusing one because MPOL_INTERLEAVE is a hint rather than a hard
requirement so it shouldn't be considered during the OOM.

The final code can be reduced to a check for MPOL_BIND which is the
only memory policy that is a hard requirement and thus relevant to a
constrained OOM logic.

[mhocko@suse.com: changelog edits]

Link: https://lkml.kernel.org/r/1622560492-1294-1-git-send-email-feng.tang@intel.com
Link: https://lkml.kernel.org/r/1622560492-1294-2-git-send-email-feng.tang@intel.com
Link: https://lkml.kernel.org/r/1622469956-82897-1-git-send-email-feng.tang@intel.com
Link: https://lkml.kernel.org/r/1622469956-82897-2-git-send-email-feng.tang@intel.com
Signed-off-by: Feng Tang <feng.tang@intel.com>
Suggested-by: Michal Hocko <mhocko@suse.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Ben Widawsky <ben.widawsky@intel.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Huang Ying <ying.huang@intel.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/mempolicy.h b/include/linux/mempolicy.h
index 5f1c74df264d1389508c8509d1f4c0da4f57646f..8773c55c7744d44530387f0a30325f6a800413d1 100644 (file)
--- a/include/linux/mempolicy.h
+++ b/include/linux/mempolicy.h
@@ -150,7 +150,7 @@ extern int huge_node(struct vm_area_struct *vma,
                                unsigned long addr, gfp_t gfp_flags,
                                struct mempolicy **mpol, nodemask_t **nodemask);
 extern bool init_nodemask_of_mempolicy(nodemask_t *mask);
-extern bool mempolicy_nodemask_intersects(struct task_struct *tsk,
+extern bool mempolicy_in_oom_domain(struct task_struct *tsk,
                                const nodemask_t *mask);
 extern nodemask_t *policy_nodemask(gfp_t gfp, struct mempolicy *policy);
 

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index b5d95bf1025d6d80ad110045df51a9b1c16385c7..bd213b900e71e3162a7c266dbb3c800270904822 100644 (file)
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -2094,16 +2094,16 @@ bool init_nodemask_of_mempolicy(nodemask_t *mask)
 #endif
 
 /*
- * mempolicy_nodemask_intersects
+ * mempolicy_in_oom_domain
  *
- * If tsk's mempolicy is "default" [NULL], return 'true' to indicate default
- * policy.  Otherwise, check for intersection between mask and the policy
- * nodemask for 'bind' or 'interleave' policy.  For 'preferred' or 'local'
- * policy, always return true since it may allocate elsewhere on fallback.
+ * If tsk's mempolicy is "bind", check for intersection between mask and
+ * the policy nodemask. Otherwise, return true for all other policies
+ * including "interleave", as a tsk with "interleave" policy may have
+ * memory allocated from all nodes in system.
  *
  * Takes task_lock(tsk) to prevent freeing of its mempolicy.
  */
-bool mempolicy_nodemask_intersects(struct task_struct *tsk,
+bool mempolicy_in_oom_domain(struct task_struct *tsk,
                                        const nodemask_t *mask)
 {
        struct mempolicy *mempolicy;
@@ -2111,29 +2111,13 @@ bool mempolicy_nodemask_intersects(struct task_struct *tsk,
 
        if (!mask)
                return ret;
+
        task_lock(tsk);
        mempolicy = tsk->mempolicy;
-       if (!mempolicy)
-               goto out;
-
-       switch (mempolicy->mode) {
-       case MPOL_PREFERRED:
-               /*
-                * MPOL_PREFERRED and MPOL_F_LOCAL are only preferred nodes to
-                * allocate from, they may fallback to other nodes when oom.
-                * Thus, it's possible for tsk to have allocated memory from
-                * nodes in mask.
-                */
-               break;
-       case MPOL_BIND:
-       case MPOL_INTERLEAVE:
+       if (mempolicy && mempolicy->mode == MPOL_BIND)
                ret = nodes_intersects(mempolicy->v.nodes, *mask);
-               break;
-       default:
-               BUG();
-       }
-out:
        task_unlock(tsk);
+
        return ret;
 }
 

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index eefd3f5fde4643791ae552a1062ce11d24b24e15..fcc29e9a30645f1377d9baa550cf840e264166c4 100644 (file)
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -104,7 +104,7 @@ static bool oom_cpuset_eligible(struct task_struct *start,
                         * mempolicy intersects current, otherwise it may be
                         * needlessly killed.
                         */
-                       ret = mempolicy_nodemask_intersects(tsk, mask);
+                       ret = mempolicy_in_oom_domain(tsk, mask);
                } else {
                        /*
                         * This is not a mempolicy constrained oom, so only