Re: [PATCH 1/2] mm: pgtable: add missing flag and statistics for kernel PTE page

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Hi Mike,

On 2024/2/4 18:58, Mike Rapoport wrote:
On Thu, Feb 01, 2024 at 04:05:40PM +0800, Qi Zheng wrote:
For kernel PTE page, we do not need to allocate and initialize its split
ptlock, but as a page table page, it's still necessary to add PG_table
flag and NR_PAGETABLE statistics for it.

Signed-off-by: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
---
  include/asm-generic/pgalloc.h |  7 ++++++-
  include/linux/mm.h            | 21 ++++++++++++++++-----
  2 files changed, 22 insertions(+), 6 deletions(-)

This should also update the architectures that define
__HAVE_ARCH_PTE_ALLOC_ONE_KERNEL, otherwise NR_PAGETABLE counts will get
wrong.

Yes, this patchset only focuses on the generic implementation. For those
architectures that define __HAVE_ARCH_PTE_ALLOC_ONE_KERNEL, some reuse
the generic __pte_alloc_one_kernel(), but some have their own customized
implementations, which indeed need to be fixed.

I wasn't familiar with those architectures and didn't investigate why
they couldn't reuse the generic __pte_alloc_one_kernel(), so I didn't
fix them. It would be better if there are maintainers corresponding to
the architecture who can help fix it. After all, they have a better
understanding of the historical background and have a testing
environment. ;)


Another related thing is that many architectures have custom allocations
for early page tables and these would also benefit form NR_PAGETABLE
accounting.

Indeed, this is also a point that can be optimized.

Thanks.

diff --git a/include/asm-generic/pgalloc.h b/include/asm-generic/pgalloc.h
index 879e5f8aa5e9..908bd9140ac2 100644
--- a/include/asm-generic/pgalloc.h
+++ b/include/asm-generic/pgalloc.h
@@ -23,6 +23,8 @@ static inline pte_t *__pte_alloc_one_kernel(struct mm_struct *mm)
if (!ptdesc)
  		return NULL;
+
+	__pagetable_pte_ctor(ptdesc);
  	return ptdesc_address(ptdesc);
  }
@@ -46,7 +48,10 @@ static inline pte_t *pte_alloc_one_kernel(struct mm_struct *mm)
   */
  static inline void pte_free_kernel(struct mm_struct *mm, pte_t *pte)
  {
-	pagetable_free(virt_to_ptdesc(pte));
+	struct ptdesc *ptdesc = virt_to_ptdesc(pte);
+
+	__pagetable_pte_dtor(ptdesc);
+	pagetable_free(ptdesc);
  }
/**
diff --git a/include/linux/mm.h b/include/linux/mm.h
index e442fd0efdd9..e37db032764e 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2922,26 +2922,37 @@ static inline bool ptlock_init(struct ptdesc *ptdesc) { return true; }
  static inline void ptlock_free(struct ptdesc *ptdesc) {}
  #endif /* USE_SPLIT_PTE_PTLOCKS */
-static inline bool pagetable_pte_ctor(struct ptdesc *ptdesc)
+static inline void __pagetable_pte_ctor(struct ptdesc *ptdesc)
  {
  	struct folio *folio = ptdesc_folio(ptdesc);
- if (!ptlock_init(ptdesc))
-		return false;
  	__folio_set_pgtable(folio);
  	lruvec_stat_add_folio(folio, NR_PAGETABLE);
+}
+
+static inline bool pagetable_pte_ctor(struct ptdesc *ptdesc)
+{
+	if (!ptlock_init(ptdesc))
+		return false;
+
+	__pagetable_pte_ctor(ptdesc);
  	return true;
  }
-static inline void pagetable_pte_dtor(struct ptdesc *ptdesc)
+static inline void __pagetable_pte_dtor(struct ptdesc *ptdesc)
  {
  	struct folio *folio = ptdesc_folio(ptdesc);
- ptlock_free(ptdesc);
  	__folio_clear_pgtable(folio);
  	lruvec_stat_sub_folio(folio, NR_PAGETABLE);
  }
+static inline void pagetable_pte_dtor(struct ptdesc *ptdesc)
+{
+	ptlock_free(ptdesc);
+	__pagetable_pte_dtor(ptdesc);
+}
+
  pte_t *__pte_offset_map(pmd_t *pmd, unsigned long addr, pmd_t *pmdvalp);
  static inline pte_t *pte_offset_map(pmd_t *pmd, unsigned long addr)
  {
--
2.30.2







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