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From: Aneesh Kumar K.V <aneesh.kumar@kernel.org>
To: Michal Hocko <mhocko@suse.com>, "Huang, Ying" <ying.huang@intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Donet Tom <donettom@linux.ibm.com>, linux-mm@kvack.org,
	linux-kernel@vger.kernel.org,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Mel Gorman <mgorman@suse.de>,
	Ben Widawsky <ben.widawsky@intel.com>,
	Feng Tang <feng.tang@intel.com>,
	Andrea Arcangeli <aarcange@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>,
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	Matthew Wilcox <willy@infradead.org>,
	Mike Kravetz <mike.kravetz@oracle.com>,
	Vlastimil Babka <vbabka@suse.cz>,
	Dan Williams <dan.j.williams@intel.com>,
	Hugh Dickins <hughd@google.com>,
	Kefeng Wang <wangkefeng.wang@huawei.com>,
	Suren Baghdasaryan <surenb@google.com>
Subject: Re: [PATCH 1/3] mm/mempolicy: Use the already fetched local variable
In-Reply-To: <ZdRq9EM1mDFXBiiO@tiehlicka>
References: <9c3f7b743477560d1c5b12b8c111a584a2cc92ee.1708097962.git.donettom@linux.ibm.com>
 <20240218133851.22c22b55460e866a099be5ce@linux-foundation.org>
 <63a0f7c4-3c3f-4097-9a24-d1e3fc7b6030@linux.ibm.com>
 <20240219172130.82a16c1ebecbf8ba86a8987d@linux-foundation.org>
 <21f343fa-84a7-4539-91e2-6fc963dbfb62@kernel.org>
 <87frxnps8w.fsf@yhuang6-desk2.ccr.corp.intel.com>
 <7097ff95-6077-4744-a770-b90d224c0c9b@kernel.org>
 <b599bfe5-1c4d-4750-b0d6-a086e1c8a34c@kernel.org>
 <8734tnppls.fsf@yhuang6-desk2.ccr.corp.intel.com>
 <ZdRq9EM1mDFXBiiO@tiehlicka>
Date: Sun, 03 Mar 2024 11:47:47 +0530
Message-ID: <875xy3ltys.fsf@kernel.org>
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Michal Hocko <mhocko@suse.com> writes:

> On Tue 20-02-24 15:22:07, Huang, Ying wrote:
> [...]
>> This isn't an issue now, because mpol_misplaced() are always called with
>> PTL held.  And, we can still keep thiscpu local variable.
>
> yes, this is the case but it would be better if we made that assumption
> official by lockdep_assert_held
>

How about this folded into this patch?

2 files changed, 12 insertions(+), 4 deletions(-)
mm/memory.c    |  6 ++++--
mm/mempolicy.c | 10 ++++++++--

modified   mm/memory.c
@@ -4879,9 +4879,11 @@ static vm_fault_t do_fault(struct vm_fault *vmf)
 	return ret;
 }
 
-int numa_migrate_prep(struct folio *folio, struct vm_area_struct *vma,
+int numa_migrate_prep(struct folio *folio, struct vm_fault *vmf,
 		      unsigned long addr, int page_nid, int *flags)
 {
+	struct vm_area_struct *vma = vmf->vma;
+
 	folio_get(folio);
 
 	/* Record the current PID acceesing VMA */
@@ -4893,7 +4895,7 @@ int numa_migrate_prep(struct folio *folio, struct vm_area_struct *vma,
 		*flags |= TNF_FAULT_LOCAL;
 	}
 
-	return mpol_misplaced(folio, vma, addr);
+	return mpol_misplaced(folio, vmf, addr);
 }
 
 static vm_fault_t do_numa_page(struct vm_fault *vmf)
modified   mm/mempolicy.c
@@ -2495,18 +2495,24 @@ static inline bool mpol_preferred_should_numa_migrate(int exec_node, int folio_n
  * Return: NUMA_NO_NODE if the page is in a node that is valid for this
  * policy, or a suitable node ID to allocate a replacement folio from.
  */
-int mpol_misplaced(struct folio *folio, struct vm_area_struct *vma,
+int mpol_misplaced(struct folio *folio, struct vm_fault *vmf,
 		   unsigned long addr)
 {
 	struct mempolicy *pol;
 	pgoff_t ilx;
 	struct zoneref *z;
 	int curnid = folio_nid(folio);
+	struct vm_area_struct *vma = vmf->vma;
 	int thiscpu = raw_smp_processor_id();
-	int thisnid = cpu_to_node(thiscpu);
+	int thisnid = numa_node_id();
 	int polnid = NUMA_NO_NODE;
 	int ret = NUMA_NO_NODE;
 
+	/*
+	 * Make sure ptl is held so that we don't preempt and we
+	 * have a stable smp processor id
+	 */
+	lockdep_assert_held(vmf->ptl);
 	pol = get_vma_policy(vma, addr, folio_order(folio), &ilx);
 	if (!(pol->flags & MPOL_F_MOF))
 		goto out;

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