linux-kernel - Re: [PATCH v3 4/4] mm/madvise: batch tlb flushes for MADV_DONTNEED[

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Message-ID: <ead4dd45-449f-4362-81d7-a25e634a4c5f@lucifer.local>
Date: Fri, 11 Apr 2025 14:10:47 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: SeongJae Park <sj@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
        "Liam R.Howlett" <howlett@...il.com>,
        David Hildenbrand <david@...hat.com>, Rik van Riel <riel@...riel.com>,
        Shakeel Butt <shakeel.butt@...ux.dev>,
        Vlastimil Babka <vbabka@...e.cz>, kernel-team@...a.com,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v3 4/4] mm/madvise: batch tlb flushes for
 MADV_DONTNEED[_LOCKED]

On Wed, Apr 09, 2025 at 05:00:22PM -0700, SeongJae Park wrote:
> MADV_DONTNEED[_LOCKED] handling for [process_]madvise() flushes tlb for
> each vma of each address range.  Update the logic to do tlb flushes in a
> batched way.  Initialize an mmu_gather object from do_madvise() and
> vector_madvise(), which are the entry level functions for
> [process_]madvise(), respectively.  And pass those objects to the
> function for per-vma work, via madvise_behavior struct.  Make the
> per-vma logic not flushes tlb on their own but just saves the tlb
> entries to the received mmu_gather object.  For this internal logic
> change, make zap_page_range_single_batched() non-static and use it
> directly from madvise_dontneed_single_vma().  Finally, the entry level
> functions flush the tlb entries that gathered for the entire user
> request, at once.
>
> Signed-off-by: SeongJae Park <sj@...nel.org>

Thanks, as usual always a pleasure to review your series :) Cheers for
these changes!

Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>

> ---
>  mm/internal.h |  3 +++
>  mm/madvise.c  | 11 ++++++++---
>  mm/memory.c   |  4 ++--
>  3 files changed, 13 insertions(+), 5 deletions(-)
>
> diff --git a/mm/internal.h b/mm/internal.h
> index ef92e88738fe..c5f9dd007215 100644
> --- a/mm/internal.h
> +++ b/mm/internal.h
> @@ -435,6 +435,9 @@ void unmap_page_range(struct mmu_gather *tlb,
>  			     struct vm_area_struct *vma,
>  			     unsigned long addr, unsigned long end,
>  			     struct zap_details *details);
> +void zap_page_range_single_batched(struct mmu_gather *tlb,
> +		struct vm_area_struct *vma, unsigned long addr,
> +		unsigned long size, struct zap_details *details);
>  int folio_unmap_invalidate(struct address_space *mapping, struct folio *folio,
>  			   gfp_t gfp);
>
> diff --git a/mm/madvise.c b/mm/madvise.c
> index 951038a9f36f..8433ac9b27e0 100644
> --- a/mm/madvise.c
> +++ b/mm/madvise.c
> @@ -851,7 +851,8 @@ static int madvise_free_single_vma(struct madvise_behavior *madv_behavior,
>   * An interface that causes the system to free clean pages and flush
>   * dirty pages is already available as msync(MS_INVALIDATE).
>   */
> -static long madvise_dontneed_single_vma(struct vm_area_struct *vma,
> +static long madvise_dontneed_single_vma(struct madvise_behavior *madv_behavior,
> +					struct vm_area_struct *vma,
>  					unsigned long start, unsigned long end)
>  {
>  	struct zap_details details = {
> @@ -859,7 +860,8 @@ static long madvise_dontneed_single_vma(struct vm_area_struct *vma,
>  		.even_cows = true,
>  	};
>
> -	zap_page_range_single(vma, start, end - start, &details);
> +	zap_page_range_single_batched(
> +			madv_behavior->tlb, vma, start, end - start, &details);
>  	return 0;
>  }
>
> @@ -950,7 +952,8 @@ static long madvise_dontneed_free(struct vm_area_struct *vma,
>  	}
>
>  	if (behavior == MADV_DONTNEED || behavior == MADV_DONTNEED_LOCKED)
> -		return madvise_dontneed_single_vma(vma, start, end);
> +		return madvise_dontneed_single_vma(
> +				madv_behavior, vma, start, end);
>  	else if (behavior == MADV_FREE)
>  		return madvise_free_single_vma(madv_behavior, vma, start, end);
>  	else
> @@ -1628,6 +1631,8 @@ static void madvise_unlock(struct mm_struct *mm, int behavior)
>  static bool madvise_batch_tlb_flush(int behavior)
>  {
>  	switch (behavior) {
> +	case MADV_DONTNEED:
> +	case MADV_DONTNEED_LOCKED:
>  	case MADV_FREE:
>  		return true;
>  	default:
> diff --git a/mm/memory.c b/mm/memory.c
> index 690695643dfb..559f3e194438 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -1998,7 +1998,7 @@ void unmap_vmas(struct mmu_gather *tlb, struct ma_state *mas,
>  	mmu_notifier_invalidate_range_end(&range);
>  }
>
> -/*
> +/**
>   * zap_page_range_single_batched - remove user pages in a given range
>   * @tlb: pointer to the caller's struct mmu_gather
>   * @vma: vm_area_struct holding the applicable pages
> @@ -2009,7 +2009,7 @@ void unmap_vmas(struct mmu_gather *tlb, struct ma_state *mas,
>   * @tlb shouldn't be NULL.  The range must fit into one VMA.  If @vma is for
>   * hugetlb, @tlb is flushed and re-initialized by this function.
>   */
> -static void zap_page_range_single_batched(struct mmu_gather *tlb,
> +void zap_page_range_single_batched(struct mmu_gather *tlb,
>  		struct vm_area_struct *vma, unsigned long address,
>  		unsigned long size, struct zap_details *details)
>  {
> --
> 2.39.5