On Thu, 1 Mar 2012, Bob Liu wrote:
> There are multi place do the same check.
>
> Signed-off-by: Bob Liu <lliubbo@xxxxxxxxx>
Combining two sets of alike changes into one function, fair enough.
But am I imagining it, or is vma going to be NULL in the callers forever
after, and KSM badly broken? And for what is vma passed to the function?
I think you want to redo this with
static struct vm_area_struct *find_mergeable_vma(struct mm_struct *mm,
unsigned long addr);
The anon_vma aspect that Andrew latched on to: that's rather a red
herring. It's not so much looking for an anon_vma, it just knows that
if an anon_vma has not (yet) been instantiated there, then it's a
waste of time to look for an Anon or KSM page in that area.
Hugh
> ---
> mm/ksm.c | 35 ++++++++++++++++++-----------------
> 1 files changed, 18 insertions(+), 17 deletions(-)
>
> diff --git a/mm/ksm.c b/mm/ksm.c
> index 8e10786..33175af 100644
> --- a/mm/ksm.c
> +++ b/mm/ksm.c
> @@ -375,11 +375,24 @@ static int break_ksm(struct vm_area_struct *vma, unsigned long addr)
> return (ret & VM_FAULT_OOM) ? -ENOMEM : 0;
> }
>
> +static int ksm_check_mm(struct mm_struct *mm, struct vm_area_struct *vma,
> + unsigned long addr)
> +{
> + if (ksm_test_exit(mm))
> + return 0;
> + vma = find_vma(mm, addr);
> + if (!vma || vma->vm_start > addr)
> + return 0;
> + if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
> + return 0;
> + return 1;
> +}
> +
> static void break_cow(struct rmap_item *rmap_item)
> {
> struct mm_struct *mm = rmap_item->mm;
> unsigned long addr = rmap_item->address;
> - struct vm_area_struct *vma;
> + struct vm_area_struct *vma = NULL;
>
> /*
> * It is not an accident that whenever we want to break COW
> @@ -388,15 +401,8 @@ static void break_cow(struct rmap_item *rmap_item)
> put_anon_vma(rmap_item->anon_vma);
>
> down_read(&mm->mmap_sem);
> - if (ksm_test_exit(mm))
> - goto out;
> - vma = find_vma(mm, addr);
> - if (!vma || vma->vm_start > addr)
> - goto out;
> - if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
> - goto out;
> - break_ksm(vma, addr);
> -out:
> + if (ksm_check_mm(mm, vma, addr))
> + break_ksm(vma, addr);
> up_read(&mm->mmap_sem);
> }
>
> @@ -418,16 +424,11 @@ static struct page *get_mergeable_page(struct rmap_item *rmap_item)
> {
> struct mm_struct *mm = rmap_item->mm;
> unsigned long addr = rmap_item->address;
> - struct vm_area_struct *vma;
> + struct vm_area_struct *vma = NULL;
> struct page *page;
>
> down_read(&mm->mmap_sem);
> - if (ksm_test_exit(mm))
> - goto out;
> - vma = find_vma(mm, addr);
> - if (!vma || vma->vm_start > addr)
> - goto out;
> - if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
> + if (!ksm_check_mm(mm, vma, addr))
> goto out;
>
> page = follow_page(vma, addr, FOLL_GET);
> --
> 1.7.0.4
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