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SubjectRe: [PATCH -V3] /proc/PID/smaps: Add PMD migration entry parsing
On Fri 03-04-20 20:30:59, Huang, Ying wrote:
> From: Huang Ying <ying.huang@intel.com>
>
> Now, when read /proc/PID/smaps, the PMD migration entry in page table is simply
> ignored. To improve the accuracy of /proc/PID/smaps, its parsing and processing
> is added.
>
> To test the patch, we run pmbench to eat 400 MB memory in background, then run
> /usr/bin/migratepages and `cat /proc/PID/smaps` every second. The issue as
> follows can be reproduced within 60 seconds.
>
> Before the patch, for the fully populated 400 MB anonymous VMA, some THP pages
> under migration may be lost as below.
>
> 7f3f6a7e5000-7f3f837e5000 rw-p 00000000 00:00 0
> Size: 409600 kB
> KernelPageSize: 4 kB
> MMUPageSize: 4 kB
> Rss: 407552 kB
> Pss: 407552 kB
> Shared_Clean: 0 kB
> Shared_Dirty: 0 kB
> Private_Clean: 0 kB
> Private_Dirty: 407552 kB
> Referenced: 301056 kB
> Anonymous: 407552 kB
> LazyFree: 0 kB
> AnonHugePages: 405504 kB
> ShmemPmdMapped: 0 kB
> FilePmdMapped: 0 kB
> Shared_Hugetlb: 0 kB
> Private_Hugetlb: 0 kB
> Swap: 0 kB
> SwapPss: 0 kB
> Locked: 0 kB
> THPeligible: 1
> VmFlags: rd wr mr mw me ac
>
> After the patch, it will be always,
>
> 7f3f6a7e5000-7f3f837e5000 rw-p 00000000 00:00 0
> Size: 409600 kB
> KernelPageSize: 4 kB
> MMUPageSize: 4 kB
> Rss: 409600 kB
> Pss: 409600 kB
> Shared_Clean: 0 kB
> Shared_Dirty: 0 kB
> Private_Clean: 0 kB
> Private_Dirty: 409600 kB
> Referenced: 294912 kB
> Anonymous: 409600 kB
> LazyFree: 0 kB
> AnonHugePages: 407552 kB
> ShmemPmdMapped: 0 kB
> FilePmdMapped: 0 kB
> Shared_Hugetlb: 0 kB
> Private_Hugetlb: 0 kB
> Swap: 0 kB
> SwapPss: 0 kB
> Locked: 0 kB
> THPeligible: 1
> VmFlags: rd wr mr mw me ac
>
> Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
> Reviewed-by: Zi Yan <ziy@nvidia.com>
> Cc: Andrea Arcangeli <aarcange@redhat.com>
> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> Cc: Vlastimil Babka <vbabka@suse.cz>
> Cc: Alexey Dobriyan <adobriyan@gmail.com>
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
> Cc: "Jérôme Glisse" <jglisse@redhat.com>
> Cc: Yang Shi <yang.shi@linux.alibaba.com>

Acked-by: Michal Hocko <mhocko@suse.com>

Thanks!

> ---
>
> v3:
>
> - Revised patch description and remove VM_WARN_ON_ONCE() per Michal's comments
>
> v2:
>
> - Use thp_migration_supported() in condition to reduce code size if THP
> migration isn't enabled.
>
> - Replace VM_BUG_ON() with VM_WARN_ON_ONCE(), it's not necessary to nuking
> kernel for this.
>
> ---
> fs/proc/task_mmu.c | 16 +++++++++++-----
> 1 file changed, 11 insertions(+), 5 deletions(-)
>
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index 8d382d4ec067..36dc7417c0df 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -546,10 +546,17 @@ static void smaps_pmd_entry(pmd_t *pmd, unsigned long addr,
> struct mem_size_stats *mss = walk->private;
> struct vm_area_struct *vma = walk->vma;
> bool locked = !!(vma->vm_flags & VM_LOCKED);
> - struct page *page;
> + struct page *page = NULL;
> +
> + if (pmd_present(*pmd)) {
> + /* FOLL_DUMP will return -EFAULT on huge zero page */
> + page = follow_trans_huge_pmd(vma, addr, pmd, FOLL_DUMP);
> + } else if (unlikely(thp_migration_supported() && is_swap_pmd(*pmd))) {
> + swp_entry_t entry = pmd_to_swp_entry(*pmd);
>
> - /* FOLL_DUMP will return -EFAULT on huge zero page */
> - page = follow_trans_huge_pmd(vma, addr, pmd, FOLL_DUMP);
> + if (is_migration_entry(entry))
> + page = migration_entry_to_page(entry);
> + }
> if (IS_ERR_OR_NULL(page))
> return;
> if (PageAnon(page))
> @@ -578,8 +585,7 @@ static int smaps_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
>
> ptl = pmd_trans_huge_lock(pmd, vma);
> if (ptl) {
> - if (pmd_present(*pmd))
> - smaps_pmd_entry(pmd, addr, walk);
> + smaps_pmd_entry(pmd, addr, walk);
> spin_unlock(ptl);
> goto out;
> }
> --
> 2.25.0

--
Michal Hocko
SUSE Labs

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