lkml.org 
[lkml]   [2023]   [Feb]   [17]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    From
    Date
    SubjectRe: [PATCH v2 09/46] mm: add MADV_SPLIT to enable HugeTLB HGM
    On Fri, Feb 17, 2023 at 4:28 PM James Houghton <jthoughton@google.com> wrote:
    >
    > 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.
    >

    So is a hugetlb page or VMA that has been MADV_SPLIT + MADV_COLLAPSE
    distinct from a hugetlb page or vma that has not been? I thought
    COLLAPSE would reverse the effects on SPLIT completely.

    > 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.
    >

    Huh, so MADV_SPLIT doesn't actually split an existing PMD mapping into
    high granularity mappings. Instead it says that future mappings may be
    high granularity? I assume they may not even be high granularity, like
    if the alias mapping faulted in a full hugetlb page (without
    UFFDIO_CONTINUE) that page would be regular mapped not high
    granularity mapped.

    This may be bikeshedding but I do think a clearer name is warranted.
    Maybe MADV_MAY_SPLIT or something.

    > More API changes may be added in the future.
    >
    > Signed-off-by: James Houghton <jthoughton@google.com>
    >
    > 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.
    > --
    > 2.39.2.637.g21b0678d19-goog
    >

    \
     
     \ /
      Last update: 2023-03-27 00:27    [W:6.196 / U:0.388 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site