linux-kernel - Re: [PATCH 1/3] mm/mempolicy: Use the already fetched local variable

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Message-ID: <87sf16bwal.fsf@yhuang6-desk2.ccr.corp.intel.com>
Date: Mon, 04 Mar 2024 09:49:54 +0800
From: "Huang, Ying" <ying.huang@...el.com>
To: Aneesh Kumar K.V <aneesh.kumar@...nel.org>
Cc: Michal Hocko <mhocko@...e.com>,  Andrew Morton
 <akpm@...ux-foundation.org>,  Donet Tom <donettom@...ux.ibm.com>,
  linux-mm@...ck.org,  linux-kernel@...r.kernel.org,  Dave Hansen
 <dave.hansen@...ux.intel.com>,  Mel Gorman <mgorman@...e.de>,  Ben
 Widawsky <ben.widawsky@...el.com>,  Feng Tang <feng.tang@...el.com>,
  Andrea Arcangeli <aarcange@...hat.com>,  Peter Zijlstra
 <peterz@...radead.org>,  Ingo Molnar <mingo@...hat.com>,  Rik van Riel
 <riel@...riel.com>,  Johannes Weiner <hannes@...xchg.org>,  Matthew Wilcox
 <willy@...radead.org>,  Mike Kravetz <mike.kravetz@...cle.com>,  Vlastimil
 Babka <vbabka@...e.cz>,  Dan Williams <dan.j.williams@...el.com>,  Hugh
 Dickins <hughd@...gle.com>,  Kefeng Wang <wangkefeng.wang@...wei.com>,
  Suren Baghdasaryan <surenb@...gle.com>
Subject: Re: [PATCH 1/3] mm/mempolicy: Use the already fetched local variable

Aneesh Kumar K.V <aneesh.kumar@...nel.org> writes:

> Michal Hocko <mhocko@...e.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;
>
> [back]
>  

LGTM, Thanks!

--
Best Regards,
Huang, Ying