Re: [PATCH 6/9] mm/memory: split non-tlb flushing part from zap_page_range_single()

Lorenzo Stoakes
2025-03-11T12:46:04Z

On Mon, Mar 10, 2025 at 10:23:15AM -0700, SeongJae Park wrote:
> Some of zap_page_range_single() callers such as [process_]madvise() with
> MADV_DONEED[_LOCKED] cannot batch tlb flushes because
> zap_page_range_single() does tlb flushing for each invocation. Split
> out the body of zap_page_range_single() except mmu_gather object
> initialization and gathered tlb entries flushing parts for such batched
> tlb flushing usage.
>
> Signed-off-by: SeongJae Park <sj@kernel.org>
> ---
> mm/memory.c | 36 ++++++++++++++++++++++--------------
> 1 file changed, 22 insertions(+), 14 deletions(-)
>
> diff --git a/mm/memory.c b/mm/memory.c
> index 78c7ee62795e..88c478e2ed1a 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -1995,38 +1995,46 @@ void unmap_vmas(struct mmu_gather *tlb, struct ma_state *mas,
> mmu_notifier_invalidate_range_end(&range);
> }
>
> -/**
> - * zap_page_range_single - remove user pages in a given range
> - * @vma: vm_area_struct holding the applicable pages
> - * @address: starting address of pages to zap
> - * @size: number of bytes to zap
> - * @details: details of shared cache invalidation
> - *
> - * The range must fit into one VMA.
> - */
> -void zap_page_range_single(struct vm_area_struct *vma, unsigned long address,
> +static void unmap_vma_single(struct mmu_gather *tlb,
> + struct vm_area_struct *vma, unsigned long address,
> unsigned long size, struct zap_details *details)
> {
> const unsigned long end = address + size;
> struct mmu_notifier_range range;
> - struct mmu_gather tlb;
>
> mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma->vm_mm,
> address, end);
> hugetlb_zap_begin(vma, &range.start, &range.end);
> - tlb_gather_mmu(&tlb, vma->vm_mm);
> update_hiwater_rss(vma->vm_mm);
> mmu_notifier_invalidate_range_start(&range);
> /*
> * unmap 'address-end' not 'range.start-range.end' as range
> * could have been expanded for hugetlb pmd sharing.
> */
> - unmap_single_vma(&tlb, vma, address, end, details, false);
> + unmap_single_vma(tlb, vma, address, end, details, false);
> mmu_notifier_invalidate_range_end(&range);
> - tlb_finish_mmu(&tlb);
> hugetlb_zap_end(vma, details);

Previously hugetlb_zap_end() would happen after tlb_finish_mmu(), now it happens
before?

This seems like a major problem with this change. If not you need to explain why
not in the commit message.

> }
>
> +/**
> + * zap_page_range_single - remove user pages in a given range
> + * @vma: vm_area_struct holding the applicable pages
> + * @address: starting address of pages to zap
> + * @size: number of bytes to zap
> + * @details: details of shared cache invalidation
> + *
> + * The range must fit into one VMA.
> + */
> +void zap_page_range_single(struct vm_area_struct *vma, unsigned long address,
> + unsigned long size, struct zap_details *details)
> +{
> + struct mmu_gather tlb;
> +
> + tlb_gather_mmu(&tlb, vma->vm_mm);
> + unmap_vma_single(&tlb, vma, address, size, details);
> + tlb_finish_mmu(&tlb);
> +}
> +
> /**
> * zap_vma_ptes - remove ptes mapping the vma
> * @vma: vm_area_struct holding ptes to be zapped
> --
> 2.39.5