On Fri, Jan 30, 2015 at 03:47:54PM +0800, Wang, Yalin wrote:
> This patch change smaps/pagemap_read pagetable walk behavior, to make
> sure not skip VM_PFNMAP pagetables,
> so that we can calculate COW pages of VM_PFNMAP as normal pages.
>
> Signed-off-by: Yalin Wang <yalin.w...@sonymobile.com>
Hi Yalin,
The original motivation of the VM_PFNMAP code in pagewalk.c comes from the
following patch:
commit a9ff785e4437c83d2179161e012f5bdfbd6381f0
Author: Cliff Wickman <c...@sgi.com>
Date: Fri May 24 15:55:36 2013 -0700
mm/pagewalk.c: walk_page_range should avoid VM_PFNMAP areas
, where Cliff stated that some kind of vma(VM_PFNMAP) caused kernel panic
when walk_page_range() was called over it. So I don't think that re-enabling
to walk over every vma(VM_PFNMAP) unexceptionally is a good idea.
If you really want to get some information from a vma(VM_PFNMAP) via these
interfaces, I recommend you to implement proper judging code which returns
0 for your vma(VM_PFNMAP) and returns 1 for Cliff's vma(VM_PFNMAP).
Thanks,
Naoya Horiguchi
> ---
> fs/proc/task_mmu.c | 2 ++
> include/linux/mm.h | 2 ++
> mm/pagewalk.c | 5 +++++
> 3 files changed, 9 insertions(+)
>
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index c7267e9..e7d7c43 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -616,6 +616,7 @@ static int show_smap(struct seq_file *m, void *v, int
> is_pid)
> struct mem_size_stats mss;
> struct mm_walk smaps_walk = {
> .pmd_entry = smaps_pte_range,
> + .test_walk = generic_walk_page_test_no_skip,
> .mm = vma->vm_mm,
> .private = &mss,
> };
> @@ -1264,6 +1265,7 @@ static ssize_t pagemap_read(struct file *file, char
> __user *buf,
>
> pagemap_walk.pmd_entry = pagemap_pte_range;
> pagemap_walk.pte_hole = pagemap_pte_hole;
> + pagemap_walk.test_walk = generic_walk_page_test_no_skip;
> #ifdef CONFIG_HUGETLB_PAGE
> pagemap_walk.hugetlb_entry = pagemap_hugetlb_range;
> #endif
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index b976d9f..07f71c5 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -1191,6 +1191,8 @@ struct mm_walk {
> void *private;
> };
>
> +int generic_walk_page_test_no_skip(unsigned long start, unsigned long end,
> + struct mm_walk *walk);
> int walk_page_range(unsigned long addr, unsigned long end,
> struct mm_walk *walk);
> int walk_page_vma(struct vm_area_struct *vma, struct mm_walk *walk);
> diff --git a/mm/pagewalk.c b/mm/pagewalk.c
> index 75c1f28..14f38d5 100644
> --- a/mm/pagewalk.c
> +++ b/mm/pagewalk.c
> @@ -206,6 +206,11 @@ static int __walk_page_range(unsigned long start,
> unsigned long end,
> return err;
> }
>
> +int generic_walk_page_test_no_skip(unsigned long start, unsigned long end,
> + struct mm_walk *walk)
> +{
> + return 0;
> +}
> /**
> * walk_page_range - walk page table with caller specific callbacks
> *
> --
> 2.2.2
> --
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