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Howlett" , Andrew Morton , Vlastimil Babka , Michal Hocko , Matthew Wilcox , Vinicius Costa Gomes , iommu@lists.linux.dev, security@kernel.org, x86@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Dave Hansen Subject: Re: [PATCH v7 7/8] mm: Introduce deferred freeing for kernel page tables Message-ID: References: <20251022082635.2462433-1-baolu.lu@linux.intel.com> <20251022082635.2462433-8-baolu.lu@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20251022082635.2462433-8-baolu.lu@linux.intel.com> X-Rspamd-Server: rspam01 X-Stat-Signature: ram4nxdtc9rz8c996sjfoktwd58n1k1x X-Rspam-User: X-Rspamd-Queue-Id: B0885180003 X-HE-Tag: 1761203415-974578 X-HE-Meta: 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 rqdA12uK d890Wc66ZIvsTtyefOWRKCM3qCwEbnhLvF4GcfuphOqqBPfx7hG6YdhNnYhpZa3+g+RHvo3GryKvuvxVUTBshTcZi0KAIGQ5tZiamXTsR0hesPnLfGccyFfSr83gvlO6iaw0pTKglbRJWDgd1B/CAvZQl38BXziWMR7ssqMHt1bq/SXjvjKtCuhppr9QlOCATzzy8oQDueTjAikBWCdHKUJbnQ4LuHocjM3aYpwVpp13aBTiMhlr81mdYAkbRxhZSJLjj7gSl30LVNh8+Sb9y8O3KcUkLbgURdvMwdSPU1f45V3RMpdoZJqD29nXQLbgjL6pMNntCKkoDX1aVaVNS23OA3GUzwoeNK33AnVtP1ISB8F4= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Oct 22, 2025 at 04:26:33PM +0800, Lu Baolu wrote: > From: Dave Hansen > > This introduces a conditional asynchronous mechanism, enabled by > CONFIG_ASYNC_KERNEL_PGTABLE_FREE. When enabled, this mechanism defers the > freeing of pages that are used as page tables for kernel address mappings. > These pages are now queued to a work struct instead of being freed > immediately. > > This deferred freeing allows for batch-freeing of page tables, providing > a safe context for performing a single expensive operation (TLB flush) > for a batch of kernel page tables instead of performing that expensive > operation for each page table. > > Signed-off-by: Dave Hansen > Signed-off-by: Lu Baolu > Reviewed-by: Jason Gunthorpe > Reviewed-by: Kevin Tian Acked-by: Mike Rapoport (Microsoft) > --- > mm/Kconfig | 3 +++ > include/linux/mm.h | 16 +++++++++++++--- > mm/pgtable-generic.c | 37 +++++++++++++++++++++++++++++++++++++ > 3 files changed, 53 insertions(+), 3 deletions(-) > > diff --git a/mm/Kconfig b/mm/Kconfig > index 0e26f4fc8717..a83df9934acd 100644 > --- a/mm/Kconfig > +++ b/mm/Kconfig > @@ -908,6 +908,9 @@ config PAGE_MAPCOUNT > config PGTABLE_HAS_HUGE_LEAVES > def_bool TRANSPARENT_HUGEPAGE || HUGETLB_PAGE > > +config ASYNC_KERNEL_PGTABLE_FREE > + def_bool n > + > # TODO: Allow to be enabled without THP > config ARCH_SUPPORTS_HUGE_PFNMAP > def_bool n > diff --git a/include/linux/mm.h b/include/linux/mm.h > index 52ae551d0eb4..d521abd33164 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -3031,6 +3031,14 @@ static inline void __pagetable_free(struct ptdesc *pt) > __free_pages(page, compound_order(page)); > } > > +#ifdef CONFIG_ASYNC_KERNEL_PGTABLE_FREE > +void pagetable_free_kernel(struct ptdesc *pt); > +#else > +static inline void pagetable_free_kernel(struct ptdesc *pt) > +{ > + __pagetable_free(pt); > +} > +#endif > /** > * pagetable_free - Free pagetables > * @pt: The page table descriptor > @@ -3040,10 +3048,12 @@ static inline void __pagetable_free(struct ptdesc *pt) > */ > static inline void pagetable_free(struct ptdesc *pt) > { > - if (ptdesc_test_kernel(pt)) > + if (ptdesc_test_kernel(pt)) { > ptdesc_clear_kernel(pt); > - > - __pagetable_free(pt); > + pagetable_free_kernel(pt); > + } else { > + __pagetable_free(pt); > + } > } > > #if defined(CONFIG_SPLIT_PTE_PTLOCKS) > diff --git a/mm/pgtable-generic.c b/mm/pgtable-generic.c > index 567e2d084071..1c7caa8ef164 100644 > --- a/mm/pgtable-generic.c > +++ b/mm/pgtable-generic.c > @@ -406,3 +406,40 @@ pte_t *__pte_offset_map_lock(struct mm_struct *mm, pmd_t *pmd, > pte_unmap_unlock(pte, ptl); > goto again; > } > + > +#ifdef CONFIG_ASYNC_KERNEL_PGTABLE_FREE > +static void kernel_pgtable_work_func(struct work_struct *work); > + > +static struct { > + struct list_head list; > + /* protect above ptdesc lists */ > + spinlock_t lock; > + struct work_struct work; > +} kernel_pgtable_work = { > + .list = LIST_HEAD_INIT(kernel_pgtable_work.list), > + .lock = __SPIN_LOCK_UNLOCKED(kernel_pgtable_work.lock), > + .work = __WORK_INITIALIZER(kernel_pgtable_work.work, kernel_pgtable_work_func), > +}; > + > +static void kernel_pgtable_work_func(struct work_struct *work) > +{ > + struct ptdesc *pt, *next; > + LIST_HEAD(page_list); > + > + spin_lock(&kernel_pgtable_work.lock); > + list_splice_tail_init(&kernel_pgtable_work.list, &page_list); > + spin_unlock(&kernel_pgtable_work.lock); > + > + list_for_each_entry_safe(pt, next, &page_list, pt_list) > + __pagetable_free(pt); > +} > + > +void pagetable_free_kernel(struct ptdesc *pt) > +{ > + spin_lock(&kernel_pgtable_work.lock); > + list_add(&pt->pt_list, &kernel_pgtable_work.list); > + spin_unlock(&kernel_pgtable_work.lock); > + > + schedule_work(&kernel_pgtable_work.work); > +} > +#endif > -- > 2.43.0 > -- Sincerely yours, Mike.