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Shutemov" , Andrea Arcangeli Subject: [PATCH v7 01/23] mm: Introduce PTE_MARKER swap entry Date: Fri, 4 Mar 2022 13:16:46 +0800 Message-Id: <20220304051708.86193-2-peterx@redhat.com> X-Mailer: git-send-email 2.32.0 In-Reply-To: <20220304051708.86193-1-peterx@redhat.com> References: <20220304051708.86193-1-peterx@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This patch introduces a new swap entry type called PTE_MARKER. It can be installed for any pte that maps a file-backed memory when the pte is temporarily zapped, so as to maintain per-pte information. The information that kept in the pte is called a "marker". Here we define the marker as "unsigned long" just to match pgoff_t, however it will only work if it still fits in swp_offset(), which is e.g. currently 58 bits on x86_64. A new config CONFIG_PTE_MARKER is introduced too; it's by default off. A bunch of helpers are defined altogether to service the rest of the pte marker code. Signed-off-by: Peter Xu --- include/asm-generic/hugetlb.h | 9 ++++ include/linux/swap.h | 15 ++++++- include/linux/swapops.h | 78 +++++++++++++++++++++++++++++++++++ mm/Kconfig | 7 ++++ 4 files changed, 108 insertions(+), 1 deletion(-) diff --git a/include/asm-generic/hugetlb.h b/include/asm-generic/hugetlb.h index 8e1e6244a89d..f39cad20ffc6 100644 --- a/include/asm-generic/hugetlb.h +++ b/include/asm-generic/hugetlb.h @@ -2,6 +2,9 @@ #ifndef _ASM_GENERIC_HUGETLB_H #define _ASM_GENERIC_HUGETLB_H +#include +#include + static inline pte_t mk_huge_pte(struct page *page, pgprot_t pgprot) { return mk_pte(page, pgprot); @@ -80,6 +83,12 @@ static inline int huge_pte_none(pte_t pte) } #endif +/* Please refer to comments above pte_none_mostly() for the usage */ +static inline int huge_pte_none_mostly(pte_t pte) +{ + return huge_pte_none(pte) || is_pte_marker(pte); +} + #ifndef __HAVE_ARCH_HUGE_PTE_WRPROTECT static inline pte_t huge_pte_wrprotect(pte_t pte) { diff --git a/include/linux/swap.h b/include/linux/swap.h index 42ebe2d6078d..20b4aceed920 100644 --- a/include/linux/swap.h +++ b/include/linux/swap.h @@ -55,6 +55,19 @@ static inline int current_is_kswapd(void) * actions on faults. */ +/* + * PTE markers are used to persist information onto PTEs that are mapped with + * file-backed memories. As its name "PTE" hints, it should only be applied to + * the leaves of pgtables. + */ +#ifdef CONFIG_PTE_MARKER +#define SWP_PTE_MARKER_NUM 1 +#define SWP_PTE_MARKER (MAX_SWAPFILES + SWP_HWPOISON_NUM + \ + SWP_MIGRATION_NUM + SWP_DEVICE_NUM) +#else +#define SWP_PTE_MARKER_NUM 0 +#endif + /* * Unaddressable device memory support. See include/linux/hmm.h and * Documentation/vm/hmm.rst. Short description is we need struct pages for @@ -100,7 +113,7 @@ static inline int current_is_kswapd(void) #define MAX_SWAPFILES \ ((1 << MAX_SWAPFILES_SHIFT) - SWP_DEVICE_NUM - \ - SWP_MIGRATION_NUM - SWP_HWPOISON_NUM) + SWP_MIGRATION_NUM - SWP_HWPOISON_NUM - SWP_PTE_MARKER_NUM) /* * Magic header for a swap area. The first part of the union is diff --git a/include/linux/swapops.h b/include/linux/swapops.h index d356ab4047f7..5103d2a4ae38 100644 --- a/include/linux/swapops.h +++ b/include/linux/swapops.h @@ -247,6 +247,84 @@ static inline int is_writable_migration_entry(swp_entry_t entry) #endif +typedef unsigned long pte_marker; + +#define PTE_MARKER_MASK (0) + +#ifdef CONFIG_PTE_MARKER + +static inline swp_entry_t make_pte_marker_entry(pte_marker marker) +{ + return swp_entry(SWP_PTE_MARKER, marker); +} + +static inline bool is_pte_marker_entry(swp_entry_t entry) +{ + return swp_type(entry) == SWP_PTE_MARKER; +} + +static inline pte_marker pte_marker_get(swp_entry_t entry) +{ + return swp_offset(entry) & PTE_MARKER_MASK; +} + +static inline bool is_pte_marker(pte_t pte) +{ + return is_swap_pte(pte) && is_pte_marker_entry(pte_to_swp_entry(pte)); +} + +#else /* CONFIG_PTE_MARKER */ + +static inline swp_entry_t make_pte_marker_entry(pte_marker marker) +{ + /* This should never be called if !CONFIG_PTE_MARKER */ + WARN_ON_ONCE(1); + return swp_entry(0, 0); +} + +static inline bool is_pte_marker_entry(swp_entry_t entry) +{ + return false; +} + +static inline pte_marker pte_marker_get(swp_entry_t entry) +{ + return 0; +} + +static inline bool is_pte_marker(pte_t pte) +{ + return false; +} + +#endif /* CONFIG_PTE_MARKER */ + +static inline pte_t make_pte_marker(pte_marker marker) +{ + return swp_entry_to_pte(make_pte_marker_entry(marker)); +} + +/* + * This is a special version to check pte_none() just to cover the case when + * the pte is a pte marker. It existed because in many cases the pte marker + * should be seen as a none pte; it's just that we have stored some information + * onto the none pte so it becomes not-none any more. + * + * It should be used when the pte is file-backed, ram-based and backing + * userspace pages, like shmem. It is not needed upon pgtables that do not + * support pte markers at all. For example, it's not needed on anonymous + * memory, kernel-only memory (including when the system is during-boot), + * non-ram based generic file-system. It's fine to be used even there, but the + * extra pte marker check will be pure overhead. + * + * For systems configured with !CONFIG_PTE_MARKER this will be automatically + * optimized to pte_none(). + */ +static inline int pte_none_mostly(pte_t pte) +{ + return pte_none(pte) || is_pte_marker(pte); +} + static inline struct page *pfn_swap_entry_to_page(swp_entry_t entry) { struct page *p = pfn_to_page(swp_offset(entry)); diff --git a/mm/Kconfig b/mm/Kconfig index c313bad5167a..25bcbb89f8e5 100644 --- a/mm/Kconfig +++ b/mm/Kconfig @@ -900,6 +900,13 @@ config ANON_VMA_NAME area from being merged with adjacent virtual memory areas due to the difference in their name. +config PTE_MARKER + def_bool n + bool "Marker PTEs support" + + help + Allows to create marker PTEs for file-backed memory. + source "mm/damon/Kconfig" endmenu -- 2.32.0