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David Alan Gilbert" , "Matthew Wilcox (Oracle)" , Vlastimil Babka , Baolin Wang , Miaohe Lin , Yang Shi , Frank van der Linden , Jiaqi Yan , linux-mm@kvack.org, linux-kernel@vger.kernel.org, James Houghton X-Spam-Status: No, score=-9.6 required=5.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_NONE, SPF_HELO_NONE,SPF_PASS,USER_IN_DEF_DKIM_WL autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1758126643688371612?= X-GMAIL-MSGID: =?utf-8?q?1758126643688371612?= Issuing ioctl(MADV_SPLIT) on a HugeTLB address range will enable HugeTLB HGM. MADV_SPLIT was chosen for the name so that this API can be applied to non-HugeTLB memory in the future, if such an application is to arise. MADV_SPLIT provides several API changes for some syscalls on HugeTLB address ranges: 1. UFFDIO_CONTINUE is allowed for MAP_SHARED VMAs at PAGE_SIZE alignment. 2. read()ing a page fault event from a userfaultfd will yield a PAGE_SIZE-rounded address, instead of a huge-page-size-rounded address (unless UFFD_FEATURE_EXACT_ADDRESS is used). There is no way to disable the API changes that come with issuing MADV_SPLIT. MADV_COLLAPSE can be used to collapse high-granularity page table mappings that come from the extended functionality that comes with using MADV_SPLIT. For post-copy live migration, the expected use-case is: 1. mmap(MAP_SHARED, some_fd) primary mapping 2. mmap(MAP_SHARED, some_fd) alias mapping 3. MADV_SPLIT the primary mapping 4. UFFDIO_REGISTER/etc. the primary mapping 5. Copy memory contents into alias mapping and UFFDIO_CONTINUE the corresponding PAGE_SIZE sections in the primary mapping. More API changes may be added in the future. Signed-off-by: James Houghton diff --git a/arch/alpha/include/uapi/asm/mman.h b/arch/alpha/include/uapi/asm/mman.h index 763929e814e9..7a26f3648b90 100644 --- a/arch/alpha/include/uapi/asm/mman.h +++ b/arch/alpha/include/uapi/asm/mman.h @@ -78,6 +78,8 @@ #define MADV_COLLAPSE 25 /* Synchronous hugepage collapse */ +#define MADV_SPLIT 26 /* Enable hugepage high-granularity APIs */ + /* compatibility flags */ #define MAP_FILE 0 diff --git a/arch/mips/include/uapi/asm/mman.h b/arch/mips/include/uapi/asm/mman.h index c6e1fc77c996..f8a74a3a0928 100644 --- a/arch/mips/include/uapi/asm/mman.h +++ b/arch/mips/include/uapi/asm/mman.h @@ -105,6 +105,8 @@ #define MADV_COLLAPSE 25 /* Synchronous hugepage collapse */ +#define MADV_SPLIT 26 /* Enable hugepage high-granularity APIs */ + /* compatibility flags */ #define MAP_FILE 0 diff --git a/arch/parisc/include/uapi/asm/mman.h b/arch/parisc/include/uapi/asm/mman.h index 68c44f99bc93..a6dc6a56c941 100644 --- a/arch/parisc/include/uapi/asm/mman.h +++ b/arch/parisc/include/uapi/asm/mman.h @@ -72,6 +72,8 @@ #define MADV_COLLAPSE 25 /* Synchronous hugepage collapse */ +#define MADV_SPLIT 74 /* Enable hugepage high-granularity APIs */ + #define MADV_HWPOISON 100 /* poison a page for testing */ #define MADV_SOFT_OFFLINE 101 /* soft offline page for testing */ diff --git a/arch/xtensa/include/uapi/asm/mman.h b/arch/xtensa/include/uapi/asm/mman.h index 1ff0c858544f..f98a77c430a9 100644 --- a/arch/xtensa/include/uapi/asm/mman.h +++ b/arch/xtensa/include/uapi/asm/mman.h @@ -113,6 +113,8 @@ #define MADV_COLLAPSE 25 /* Synchronous hugepage collapse */ +#define MADV_SPLIT 26 /* Enable hugepage high-granularity APIs */ + /* compatibility flags */ #define MAP_FILE 0 diff --git a/include/uapi/asm-generic/mman-common.h b/include/uapi/asm-generic/mman-common.h index 6ce1f1ceb432..996e8ded092f 100644 --- a/include/uapi/asm-generic/mman-common.h +++ b/include/uapi/asm-generic/mman-common.h @@ -79,6 +79,8 @@ #define MADV_COLLAPSE 25 /* Synchronous hugepage collapse */ +#define MADV_SPLIT 26 /* Enable hugepage high-granularity APIs */ + /* compatibility flags */ #define MAP_FILE 0 diff --git a/mm/madvise.c b/mm/madvise.c index c2202f51e9dd..8c004c678262 100644 --- a/mm/madvise.c +++ b/mm/madvise.c @@ -1006,6 +1006,28 @@ static long madvise_remove(struct vm_area_struct *vma, return error; } +static int madvise_split(struct vm_area_struct *vma, + unsigned long *new_flags) +{ +#ifdef CONFIG_HUGETLB_HIGH_GRANULARITY_MAPPING + if (!is_vm_hugetlb_page(vma) || !hugetlb_hgm_eligible(vma)) + return -EINVAL; + + /* + * PMD sharing doesn't work with HGM. If this MADV_SPLIT is on part + * of a VMA, then we will split the VMA. Here, we're unsharing before + * splitting because it's simpler, although we may be unsharing more + * than we need. + */ + hugetlb_unshare_all_pmds(vma); + + *new_flags |= VM_HUGETLB_HGM; + return 0; +#else + return -EINVAL; +#endif +} + /* * Apply an madvise behavior to a region of a vma. madvise_update_vma * will handle splitting a vm area into separate areas, each area with its own @@ -1084,6 +1106,11 @@ static int madvise_vma_behavior(struct vm_area_struct *vma, break; case MADV_COLLAPSE: return madvise_collapse(vma, prev, start, end); + case MADV_SPLIT: + error = madvise_split(vma, &new_flags); + if (error) + goto out; + break; } anon_name = anon_vma_name(vma); @@ -1178,6 +1205,9 @@ madvise_behavior_valid(int behavior) case MADV_HUGEPAGE: case MADV_NOHUGEPAGE: case MADV_COLLAPSE: +#endif +#ifdef CONFIG_HUGETLB_HIGH_GRANULARITY_MAPPING + case MADV_SPLIT: #endif case MADV_DONTDUMP: case MADV_DODUMP: @@ -1368,6 +1398,8 @@ int madvise_set_anon_name(struct mm_struct *mm, unsigned long start, * transparent huge pages so the existing pages will not be * coalesced into THP and new pages will not be allocated as THP. * MADV_COLLAPSE - synchronously coalesce pages into new THP. + * MADV_SPLIT - allow HugeTLB pages to be mapped at PAGE_SIZE. This allows + * UFFDIO_CONTINUE to accept PAGE_SIZE-aligned regions. * MADV_DONTDUMP - the application wants to prevent pages in the given range * from being included in its core dump. * MADV_DODUMP - cancel MADV_DONTDUMP: no longer exclude from core dump.