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    Subject[PATCH 1/4] madvice: add MADV_SHAREABLE and MADV_UNSHAREABLE calls.
    Date
    This patch add MADV_SHAREABLE and MADV_UNSHAREABLE madvise calls,
    this calls used to mark vm memory areas with the VM_MERGEABLE flag,
    that specific if the memory inside the vma is allowed to be dinamicly shared
    with other memorys.

    (this is needed for ksm vma scanning support)

    Signed-off-by: Izik Eidus <ieidus@redhat.com>
    ---
    include/asm-generic/mman.h | 2 +
    include/linux/mm.h | 2 +
    include/linux/sched.h | 2 +
    mm/madvise.c | 116 +++++++++++++++++++++++++++++++++----------
    4 files changed, 95 insertions(+), 27 deletions(-)

    diff --git a/include/asm-generic/mman.h b/include/asm-generic/mman.h
    index 5e3dde2..830295d 100644
    --- a/include/asm-generic/mman.h
    +++ b/include/asm-generic/mman.h
    @@ -34,6 +34,8 @@
    #define MADV_REMOVE 9 /* remove these pages & resources */
    #define MADV_DONTFORK 10 /* don't inherit across fork */
    #define MADV_DOFORK 11 /* do inherit across fork */
    +#define MADV_SHAREABLE 12 /* can share identical pages */
    +#define MADV_UNSHAREABLE 13 /* can not share identical pages */

    /* compatibility flags */
    #define MAP_FILE 0
    diff --git a/include/linux/mm.h b/include/linux/mm.h
    index a0ddfb5..61328a4 100644
    --- a/include/linux/mm.h
    +++ b/include/linux/mm.h
    @@ -106,6 +106,8 @@ extern unsigned int kobjsize(const void *objp);
    #define VM_SAO 0x20000000 /* Strong Access Ordering (powerpc) */
    #define VM_PFN_AT_MMAP 0x40000000 /* PFNMAP vma that is fully mapped at mmap time */

    +#define VM_MERGEABLE 0x80000000 /* Memory may be merged */
    +
    #ifndef VM_STACK_DEFAULT_FLAGS /* arch can override this */
    #define VM_STACK_DEFAULT_FLAGS VM_DATA_DEFAULT_FLAGS
    #endif
    diff --git a/include/linux/sched.h b/include/linux/sched.h
    index b4c38bc..7dc786a 100644
    --- a/include/linux/sched.h
    +++ b/include/linux/sched.h
    @@ -439,6 +439,8 @@ extern int get_dumpable(struct mm_struct *mm);
    # define MMF_DUMP_MASK_DEFAULT_ELF 0
    #endif

    +#define MMF_VM_MERGEABLE 9
    +
    struct sighand_struct {
    atomic_t count;
    struct k_sigaction action[_NSIG];
    diff --git a/mm/madvise.c b/mm/madvise.c
    index b9ce574..bd215ce 100644
    --- a/mm/madvise.c
    +++ b/mm/madvise.c
    @@ -30,36 +30,12 @@ static int madvise_need_mmap_write(int behavior)
    }
    }

    -/*
    - * We can potentially split a vm area into separate
    - * areas, each area with its own behavior.
    - */
    -static long madvise_behavior(struct vm_area_struct * vma,
    - struct vm_area_struct **prev,
    - unsigned long start, unsigned long end, int behavior)
    +static int handle_vmas(struct vm_area_struct *vma, struct vm_area_struct **prev,
    + unsigned long start, unsigned long end, int new_flags)
    {
    struct mm_struct * mm = vma->vm_mm;
    - int error = 0;
    pgoff_t pgoff;
    - int new_flags = vma->vm_flags;
    -
    - switch (behavior) {
    - case MADV_NORMAL:
    - new_flags = new_flags & ~VM_RAND_READ & ~VM_SEQ_READ;
    - break;
    - case MADV_SEQUENTIAL:
    - new_flags = (new_flags & ~VM_RAND_READ) | VM_SEQ_READ;
    - break;
    - case MADV_RANDOM:
    - new_flags = (new_flags & ~VM_SEQ_READ) | VM_RAND_READ;
    - break;
    - case MADV_DONTFORK:
    - new_flags |= VM_DONTCOPY;
    - break;
    - case MADV_DOFORK:
    - new_flags &= ~VM_DONTCOPY;
    - break;
    - }
    + int error = 0;

    if (new_flags == vma->vm_flags) {
    *prev = vma;
    @@ -101,6 +77,37 @@ out:
    }

    /*
    + * We can potentially split a vm area into separate
    + * areas, each area with its own behavior.
    + */
    +static long madvise_behavior(struct vm_area_struct * vma,
    + struct vm_area_struct **prev,
    + unsigned long start, unsigned long end, int behavior)
    +{
    + int new_flags = vma->vm_flags;
    +
    + switch (behavior) {
    + case MADV_NORMAL:
    + new_flags = new_flags & ~VM_RAND_READ & ~VM_SEQ_READ;
    + break;
    + case MADV_SEQUENTIAL:
    + new_flags = (new_flags & ~VM_RAND_READ) | VM_SEQ_READ;
    + break;
    + case MADV_RANDOM:
    + new_flags = (new_flags & ~VM_SEQ_READ) | VM_RAND_READ;
    + break;
    + case MADV_DONTFORK:
    + new_flags |= VM_DONTCOPY;
    + break;
    + case MADV_DOFORK:
    + new_flags &= ~VM_DONTCOPY;
    + break;
    + }
    +
    + return handle_vmas(vma, prev, start, end, new_flags);
    +}
    +
    +/*
    * Schedule all required I/O operations. Do not wait for completion.
    */
    static long madvise_willneed(struct vm_area_struct * vma,
    @@ -208,6 +215,54 @@ static long madvise_remove(struct vm_area_struct *vma,
    return error;
    }

    +/*
    + * Application allows pages to be shared with other pages of identical
    + * content.
    + *
    + */
    +static long madvise_shareable(struct vm_area_struct *vma,
    + struct vm_area_struct **prev,
    + unsigned long start, unsigned long end,
    + int behavior)
    +{
    + int ret;
    + struct mm_struct *mm;
    +
    + switch (behavior) {
    +#if defined(CONFIG_KSM) || defined(CONFIG_KSM_MODULE)
    + case MADV_SHAREABLE:
    + ret = handle_vmas(vma, prev, start, end,
    + vma->vm_flags | VM_MERGEABLE);
    +
    + if (!ret) {
    + mm = vma->vm_mm;
    + set_bit(MMF_VM_MERGEABLE, &mm->flags);
    + }
    +
    + return ret;
    + case MADV_UNSHAREABLE:
    + ret = handle_vmas(vma, prev, start, end,
    + vma->vm_flags & ~VM_MERGEABLE);
    +
    + if (!ret) {
    + mm = vma->vm_mm;
    + vma = mm->mmap;
    + while (vma) {
    + if (vma->vm_flags & VM_MERGEABLE)
    + break;
    + vma = vma->vm_next;
    + }
    + if (!vma)
    + clear_bit(MMF_VM_MERGEABLE, &mm->flags);
    + }
    +
    + return ret;
    +#endif
    + default:
    + return -EINVAL;
    + }
    +}
    +
    static long
    madvise_vma(struct vm_area_struct *vma, struct vm_area_struct **prev,
    unsigned long start, unsigned long end, int behavior)
    @@ -238,6 +293,11 @@ madvise_vma(struct vm_area_struct *vma, struct vm_area_struct **prev,
    error = madvise_dontneed(vma, prev, start, end);
    break;

    + case MADV_SHAREABLE:
    + case MADV_UNSHAREABLE:
    + error = madvise_shareable(vma, prev, start, end, behavior);
    + break;
    +
    default:
    error = -EINVAL;
    break;
    @@ -269,6 +329,8 @@ madvise_vma(struct vm_area_struct *vma, struct vm_area_struct **prev,
    * so the kernel can free resources associated with it.
    * MADV_REMOVE - the application wants to free up the given range of
    * pages and associated backing store.
    + * MADV_SHAREABLE - the application agrees that pages in the given
    + * range can be shared w/ other pages of identical content.
    *
    * return values:
    * zero - success
    --
    1.5.6.5


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