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Message-Id: <20230518171323.83828-1-sj@kernel.org>
Date: Thu, 18 May 2023 17:13:23 +0000
From: SeongJae Park <sj@...nel.org>
To: Ryan Roberts <ryan.roberts@....com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
SeongJae Park <sj@...nel.org>,
Christoph Hellwig <hch@...radead.org>,
"Matthew Wilcox (Oracle)" <willy@...radead.org>,
"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
Lorenzo Stoakes <lstoakes@...il.com>,
Uladzislau Rezki <urezki@...il.com>, Zi Yan <ziy@...dia.com>,
linux-kernel@...r.kernel.org, linux-mm@...ck.org,
damon@...ts.linux.dev
Subject: Re: [PATCH v2 2/5] mm: damon must atomically clear young on ptes and pmds
Hi Ryan,
Nit. For consistency of DAMON commits subjects, I'd prefer something like
"mm/damon/ops-common: atomically test and clear young on ptes and pmds".
On Thu, 18 May 2023 12:07:24 +0100 Ryan Roberts <ryan.roberts@....com> wrote:
> It is racy to non-atomically read a pte, then clear the young bit, then
> write it back as this could discard dirty information. Further, it is
> bad practice to directly set a pte entry within a table. Instead
> clearing young must go through the arch-provided helper,
> ptep_test_and_clear_young() to ensure it is modified atomically and to
> give the arch code visibility and allow it to check (and potentially
> modify) the operation.
>
> Fixes: 46c3a0accdc4 ("mm/damon/vaddr: separate commonly usable functions")
Nit. The commit is only for refactoring. The original code camde from commit
3f49584b262c ("mm/damon: implement primitives for the virtual memory address
spaces").
> Signed-off-by: Ryan Roberts <ryan.roberts@....com>
> Reviewed-by: Zi Yan <ziy@...dia.com>
Other than above nits,
Reviewed-by: SeongJae Park <sj@...nel.org>
Thanks,
SJ
> ---
> mm/damon/ops-common.c | 16 ++++++----------
> mm/damon/ops-common.h | 4 ++--
> mm/damon/paddr.c | 4 ++--
> mm/damon/vaddr.c | 4 ++--
> 4 files changed, 12 insertions(+), 16 deletions(-)
>
> diff --git a/mm/damon/ops-common.c b/mm/damon/ops-common.c
> index cc63cf953636..acc264b97903 100644
> --- a/mm/damon/ops-common.c
> +++ b/mm/damon/ops-common.c
> @@ -37,7 +37,7 @@ struct folio *damon_get_folio(unsigned long pfn)
> return folio;
> }
>
> -void damon_ptep_mkold(pte_t *pte, struct mm_struct *mm, unsigned long addr)
> +void damon_ptep_mkold(pte_t *pte, struct vm_area_struct *vma, unsigned long addr)
> {
> bool referenced = false;
> struct folio *folio = damon_get_folio(pte_pfn(*pte));
> @@ -45,13 +45,11 @@ void damon_ptep_mkold(pte_t *pte, struct mm_struct *mm, unsigned long addr)
> if (!folio)
> return;
>
> - if (pte_young(*pte)) {
> + if (ptep_test_and_clear_young(vma, addr, pte))
> referenced = true;
> - *pte = pte_mkold(*pte);
> - }
>
> #ifdef CONFIG_MMU_NOTIFIER
> - if (mmu_notifier_clear_young(mm, addr, addr + PAGE_SIZE))
> + if (mmu_notifier_clear_young(vma->vm_mm, addr, addr + PAGE_SIZE))
> referenced = true;
> #endif /* CONFIG_MMU_NOTIFIER */
>
> @@ -62,7 +60,7 @@ void damon_ptep_mkold(pte_t *pte, struct mm_struct *mm, unsigned long addr)
> folio_put(folio);
> }
>
> -void damon_pmdp_mkold(pmd_t *pmd, struct mm_struct *mm, unsigned long addr)
> +void damon_pmdp_mkold(pmd_t *pmd, struct vm_area_struct *vma, unsigned long addr)
> {
> #ifdef CONFIG_TRANSPARENT_HUGEPAGE
> bool referenced = false;
> @@ -71,13 +69,11 @@ void damon_pmdp_mkold(pmd_t *pmd, struct mm_struct *mm, unsigned long addr)
> if (!folio)
> return;
>
> - if (pmd_young(*pmd)) {
> + if (pmdp_test_and_clear_young(vma, addr, pmd))
> referenced = true;
> - *pmd = pmd_mkold(*pmd);
> - }
>
> #ifdef CONFIG_MMU_NOTIFIER
> - if (mmu_notifier_clear_young(mm, addr, addr + HPAGE_PMD_SIZE))
> + if (mmu_notifier_clear_young(vma->vm_mm, addr, addr + HPAGE_PMD_SIZE))
> referenced = true;
> #endif /* CONFIG_MMU_NOTIFIER */
>
> diff --git a/mm/damon/ops-common.h b/mm/damon/ops-common.h
> index 14f4bc69f29b..18d837d11bce 100644
> --- a/mm/damon/ops-common.h
> +++ b/mm/damon/ops-common.h
> @@ -9,8 +9,8 @@
>
> struct folio *damon_get_folio(unsigned long pfn);
>
> -void damon_ptep_mkold(pte_t *pte, struct mm_struct *mm, unsigned long addr);
> -void damon_pmdp_mkold(pmd_t *pmd, struct mm_struct *mm, unsigned long addr);
> +void damon_ptep_mkold(pte_t *pte, struct vm_area_struct *vma, unsigned long addr);
> +void damon_pmdp_mkold(pmd_t *pmd, struct vm_area_struct *vma, unsigned long addr);
>
> int damon_cold_score(struct damon_ctx *c, struct damon_region *r,
> struct damos *s);
> diff --git a/mm/damon/paddr.c b/mm/damon/paddr.c
> index 467b99166b43..5b3a3463d078 100644
> --- a/mm/damon/paddr.c
> +++ b/mm/damon/paddr.c
> @@ -24,9 +24,9 @@ static bool __damon_pa_mkold(struct folio *folio, struct vm_area_struct *vma,
> while (page_vma_mapped_walk(&pvmw)) {
> addr = pvmw.address;
> if (pvmw.pte)
> - damon_ptep_mkold(pvmw.pte, vma->vm_mm, addr);
> + damon_ptep_mkold(pvmw.pte, vma, addr);
> else
> - damon_pmdp_mkold(pvmw.pmd, vma->vm_mm, addr);
> + damon_pmdp_mkold(pvmw.pmd, vma, addr);
> }
> return true;
> }
> diff --git a/mm/damon/vaddr.c b/mm/damon/vaddr.c
> index 1fec16d7263e..37994fb6120c 100644
> --- a/mm/damon/vaddr.c
> +++ b/mm/damon/vaddr.c
> @@ -311,7 +311,7 @@ static int damon_mkold_pmd_entry(pmd_t *pmd, unsigned long addr,
> }
>
> if (pmd_trans_huge(*pmd)) {
> - damon_pmdp_mkold(pmd, walk->mm, addr);
> + damon_pmdp_mkold(pmd, walk->vma, addr);
> spin_unlock(ptl);
> return 0;
> }
> @@ -323,7 +323,7 @@ static int damon_mkold_pmd_entry(pmd_t *pmd, unsigned long addr,
> pte = pte_offset_map_lock(walk->mm, pmd, addr, &ptl);
> if (!pte_present(*pte))
> goto out;
> - damon_ptep_mkold(pte, walk->mm, addr);
> + damon_ptep_mkold(pte, walk->vma, addr);
> out:
> pte_unmap_unlock(pte, ptl);
> return 0;
> --
> 2.25.1
>
>
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