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SubjectRe: [PATCH v4] Add /proc/PID/smaps support for DAX
On Wed, Oct 25, 2017 at 10:13 PM, Fan Du <fan.du@intel.com> wrote:
>
> Memory behind device DAX is not attached into normal memory
> management system, when user mmap /dev/dax, smaps part is
> currently missing, so no idea for user to check how much
> device DAX memory are actually used in practice.
>
> Whether vma is backed up by normal page,huge page, or both
> at the same time, this makes no difference for device DAX
> user so far.
>
> Using existing smaps structure is enough to do the job, so
> this patch tries to use existing RSS/PSS stuff for statistics.
> An example reading is like this:
> ----------------------------------------------------
> 7f30fe200000-7f3102200000 rw-s 00000000 00:06 19567 /dev/dax12.0
> Size: 65536 kB
> KernelPageSize: 4 kB
> MMUPageSize: 4 kB
> Rss: 65536 kB
> Pss: 65536 kB
> Shared_Clean: 0 kB
> Shared_Dirty: 0 kB
> Private_Clean: 0 kB
> Private_Dirty: 65536 kB
> Referenced: 65536 kB
> Anonymous: 0 kB
> LazyFree: 0 kB
> AnonHugePages: 0 kB
> ShmemPmdMapped: 0 kB
> Shared_Hugetlb: 0 kB
> Private_Hugetlb: 0 kB
> Swap: 0 kB
> SwapPss: 0 kB
> Locked: 65536 kB
> ProtectionKey: 0
> VmFlags: rd wr sh mr mw me ms mm hg
>
> Signed-off-by: Fan Du <fan.du@intel.com>
> ---
> v4:
> * Merge device DAX readings into existing smap counters
> for simplicity.
>
> v3:
> * Elaborate more about the usage suggested by Michal Hocko
>
> v2:
> * Using pte_devmap to check valid pfn page structure,
> Pointed out by Dan. thx!
> fs/proc/task_mmu.c | 74 ++++++++++++++++++++++++++++++++++++++++++++++++++++--
> 1 file changed, 72 insertions(+), 2 deletions(-)
>
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index 5589b4b..9b2d3e6 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -507,6 +507,55 @@ static void smaps_account(struct mem_size_stats *mss, struct page *page,
> }
> }
>
> +/* page structure behind DAX mappings is NOT compound page
> + * when it's a huge page mappings, so introduce new API to
> + * account for both PMD and PUD mapping.
> + */
> +static void smaps_account_dax_huge(struct mem_size_stats *mss,
> + struct page *page, unsigned long size, bool young, bool dirty)
> +{
> + int mapcount = page_mapcount(page);
> +
> + if (PageAnon(page)) {
> + mss->anonymous += size;
> + if (!PageSwapBacked(page) && !dirty && !PageDirty(page))
> + mss->lazyfree += size;
> + }
> +
> + mss->resident += size;
> + /* Accumulate the size in pages that have been accessed. */
> + if (young || page_is_young(page) || PageReferenced(page))
> + mss->referenced += size;
> +
> + /*
> + * page_count(page) == 1 guarantees the page is mapped exactly once.
> + * If any subpage of the compound page mapped with PTE it would elevate
> + * page_count().
> + */
> + if (page_count(page) == 1) {
> + if (dirty || PageDirty(page))
> + mss->private_dirty += size;
> + else
> + mss->private_clean += size;
> + mss->pss += (u64)size << PSS_SHIFT;
> + return;
> + }
> +
> + if (mapcount >= 2) {
> + if (dirty || PageDirty(page))
> + mss->shared_dirty += size;
> + else
> + mss->shared_clean += size;
> + mss->pss += (size << PSS_SHIFT) / mapcount;
> + } else {
> + if (dirty || PageDirty(page))
> + mss->private_dirty += size;
> + else
> + mss->private_clean += size;
> + mss->pss += size << PSS_SHIFT;
> + }
> +}
> +
> #ifdef CONFIG_SHMEM
> static int smaps_pte_hole(unsigned long addr, unsigned long end,
> struct mm_walk *walk)
> @@ -528,7 +577,16 @@ static void smaps_pte_entry(pte_t *pte, unsigned long addr,
> struct page *page = NULL;
>
> if (pte_present(*pte)) {
> - page = vm_normal_page(vma, addr, *pte);
> + if (!vma_is_dax(vma))
> + page = vm_normal_page(vma, addr, *pte);
> + else if (pte_devmap(*pte)) {
> + struct dev_pagemap *pgmap;
> +
> + pgmap = get_dev_pagemap(pte_pfn(*pte), NULL);

Where do you do the put_dev_pagemap?

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