| Message ID | 63f0b3d2f9124ae5076963fb5505bd36daba0393.1706774109.git.zhengqi.arch@bytedance.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [1/2] mm: pgtable: add missing flag and statistics for kernel PTE page | expand |
> On Feb 1, 2024, at 16:05, Qi Zheng <zhengqi.arch@bytedance.com> wrote: > > For kernel PMD entry, we use init_mm.page_table_lock to protect it, so > there is no need to allocate and initialize the split ptlock for kernel > PMD page. > > Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com> Reviewed-by: Muchun Song <muchun.song@linux.dev> Thanks.
On Thu, Feb 01, 2024 at 04:05:41PM +0800, Qi Zheng wrote: > For kernel PMD entry, we use init_mm.page_table_lock to protect it, so > there is no need to allocate and initialize the split ptlock for kernel > PMD page. I don't think this is a great idea. Maybe there's no need to initialise it, but keeping things the same between kernel & user page tables is a usually better. We don't normally allocate memory for the spinlock, it's only in debugging scenarios like LOCKDEP. I would drop this unless you have a really compelling argument to make.
Hi Matthew, On 2024/2/5 02:54, Matthew Wilcox wrote: > On Thu, Feb 01, 2024 at 04:05:41PM +0800, Qi Zheng wrote: >> For kernel PMD entry, we use init_mm.page_table_lock to protect it, so >> there is no need to allocate and initialize the split ptlock for kernel >> PMD page. > > I don't think this is a great idea. Maybe there's no need to initialise > it, but keeping things the same between kernel & user page tables is a > usually better. We don't normally allocate memory for the spinlock, > it's only in debugging scenarios like LOCKDEP. I would drop this unless > you have a really compelling argument to make. The reason I first noticed this is that we didn't allocate and initialize the ptlock in __pte_alloc_one_kernel(). So in at the PTE level, the implementation of kernel & user page tables is already different. Thanks.
diff --git a/include/asm-generic/pgalloc.h b/include/asm-generic/pgalloc.h index 908bd9140ac2..57bd41adf760 100644 --- a/include/asm-generic/pgalloc.h +++ b/include/asm-generic/pgalloc.h @@ -139,7 +139,10 @@ static inline pmd_t *pmd_alloc_one(struct mm_struct *mm, unsigned long addr) ptdesc = pagetable_alloc(gfp, 0); if (!ptdesc) return NULL; - if (!pagetable_pmd_ctor(ptdesc)) { + + if (mm == &init_mm) { + __pagetable_pmd_ctor(ptdesc); + } else if (!pagetable_pmd_ctor(ptdesc)) { pagetable_free(ptdesc); return NULL; } @@ -153,7 +156,10 @@ static inline void pmd_free(struct mm_struct *mm, pmd_t *pmd) struct ptdesc *ptdesc = virt_to_ptdesc(pmd); BUG_ON((unsigned long)pmd & (PAGE_SIZE-1)); - pagetable_pmd_dtor(ptdesc); + if (mm == &init_mm) + __pagetable_pmd_dtor(ptdesc); + else + pagetable_pmd_dtor(ptdesc); pagetable_free(ptdesc); } #endif diff --git a/include/linux/mm.h b/include/linux/mm.h index e37db032764e..68ca71407177 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -3048,26 +3048,37 @@ static inline spinlock_t *pmd_lock(struct mm_struct *mm, pmd_t *pmd) return ptl; } -static inline bool pagetable_pmd_ctor(struct ptdesc *ptdesc) +static inline void __pagetable_pmd_ctor(struct ptdesc *ptdesc) { struct folio *folio = ptdesc_folio(ptdesc); - if (!pmd_ptlock_init(ptdesc)) - return false; __folio_set_pgtable(folio); lruvec_stat_add_folio(folio, NR_PAGETABLE); +} + +static inline bool pagetable_pmd_ctor(struct ptdesc *ptdesc) +{ + if (!pmd_ptlock_init(ptdesc)) + return false; + + __pagetable_pmd_ctor(ptdesc); return true; } -static inline void pagetable_pmd_dtor(struct ptdesc *ptdesc) +static inline void __pagetable_pmd_dtor(struct ptdesc *ptdesc) { struct folio *folio = ptdesc_folio(ptdesc); - pmd_ptlock_free(ptdesc); __folio_clear_pgtable(folio); lruvec_stat_sub_folio(folio, NR_PAGETABLE); } +static inline void pagetable_pmd_dtor(struct ptdesc *ptdesc) +{ + pmd_ptlock_free(ptdesc); + __pagetable_pmd_dtor(ptdesc); +} + /* * No scalability reason to split PUD locks yet, but follow the same pattern * as the PMD locks to make it easier if we decide to. The VM should not be
For kernel PMD entry, we use init_mm.page_table_lock to protect it, so there is no need to allocate and initialize the split ptlock for kernel PMD page. Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com> --- include/asm-generic/pgalloc.h | 10 ++++++++-- include/linux/mm.h | 21 ++++++++++++++++----- 2 files changed, 24 insertions(+), 7 deletions(-)