Re: [PATCH -V14 3/3] memory tiering: skip to scan fast memory

[Yang Shi <shy828301@gmail.com>]

On Tue, Mar 1, 2022 at 12:54 AM Huang Ying <ying.huang@intel.com> wrote:
>
> If the NUMA balancing isn't used to optimize the page placement among
> sockets but only among memory types, the hot pages in the fast memory
> node couldn't be migrated (promoted) to anywhere.  So it's unnecessary
> to scan the pages in the fast memory node via changing their PTE/PMD
> mapping to be PROT_NONE.  So that the page faults could be avoided
> too.
>
> In the test, if only the memory tiering NUMA balancing mode is enabled, the
> number of the NUMA balancing hint faults for the DRAM node is reduced to
> almost 0 with the patch.  While the benchmark score doesn't change
> visibly.

Reviewed-by: Yang Shi <shy828301@gmail.com>

>
> Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
> Suggested-by: Dave Hansen <dave.hansen@linux.intel.com>
> Tested-by: Baolin Wang <baolin.wang@linux.alibaba.com>
> Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
> Acked-by: Johannes Weiner <hannes@cmpxchg.org>
> Reviewed-by: Oscar Salvador <osalvador@suse.de>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: Rik van Riel <riel@surriel.com>
> Cc: Mel Gorman <mgorman@techsingularity.net>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Yang Shi <shy828301@gmail.com>
> Cc: Zi Yan <ziy@nvidia.com>
> Cc: Wei Xu <weixugc@google.com>
> Cc: Shakeel Butt <shakeelb@google.com>
> Cc: zhongjiang-ali <zhongjiang-ali@linux.alibaba.com>
> Cc: linux-kernel@vger.kernel.org
> Cc: linux-mm@kvack.org
> ---
>  mm/huge_memory.c | 30 +++++++++++++++++++++---------
>  mm/mprotect.c    | 13 ++++++++++++-
>  2 files changed, 33 insertions(+), 10 deletions(-)
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 406a3c28c026..9ce126cb0cfd 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -34,6 +34,7 @@
>  #include <linux/oom.h>
>  #include <linux/numa.h>
>  #include <linux/page_owner.h>
> +#include <linux/sched/sysctl.h>
>
>  #include <asm/tlb.h>
>  #include <asm/pgalloc.h>
> @@ -1766,17 +1767,28 @@ int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
>         }
>  #endif
>
> -       /*
> -        * Avoid trapping faults against the zero page. The read-only
> -        * data is likely to be read-cached on the local CPU and
> -        * local/remote hits to the zero page are not interesting.
> -        */
> -       if (prot_numa && is_huge_zero_pmd(*pmd))
> -               goto unlock;
> +       if (prot_numa) {
> +               struct page *page;
> +               /*
> +                * Avoid trapping faults against the zero page. The read-only
> +                * data is likely to be read-cached on the local CPU and
> +                * local/remote hits to the zero page are not interesting.
> +                */
> +               if (is_huge_zero_pmd(*pmd))
> +                       goto unlock;
>
> -       if (prot_numa && pmd_protnone(*pmd))
> -               goto unlock;
> +               if (pmd_protnone(*pmd))
> +                       goto unlock;
>
> +               page = pmd_page(*pmd);
> +               /*
> +                * Skip scanning top tier node if normal numa
> +                * balancing is disabled
> +                */
> +               if (!(sysctl_numa_balancing_mode & NUMA_BALANCING_NORMAL) &&
> +                   node_is_toptier(page_to_nid(page)))
> +                       goto unlock;
> +       }
>         /*
>          * In case prot_numa, we are under mmap_read_lock(mm). It's critical
>          * to not clear pmd intermittently to avoid race with MADV_DONTNEED
> diff --git a/mm/mprotect.c b/mm/mprotect.c
> index 0138dfcdb1d8..2fe03e695c81 100644
> --- a/mm/mprotect.c
> +++ b/mm/mprotect.c
> @@ -29,6 +29,7 @@
>  #include <linux/uaccess.h>
>  #include <linux/mm_inline.h>
>  #include <linux/pgtable.h>
> +#include <linux/sched/sysctl.h>
>  #include <asm/cacheflush.h>
>  #include <asm/mmu_context.h>
>  #include <asm/tlbflush.h>
> @@ -83,6 +84,7 @@ static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
>                          */
>                         if (prot_numa) {
>                                 struct page *page;
> +                               int nid;
>
>                                 /* Avoid TLB flush if possible */
>                                 if (pte_protnone(oldpte))
> @@ -109,7 +111,16 @@ static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
>                                  * Don't mess with PTEs if page is already on the node
>                                  * a single-threaded process is running on.
>                                  */
> -                               if (target_node == page_to_nid(page))
> +                               nid = page_to_nid(page);
> +                               if (target_node == nid)
> +                                       continue;
> +
> +                               /*
> +                                * Skip scanning top tier node if normal numa
> +                                * balancing is disabled
> +                                */
> +                               if (!(sysctl_numa_balancing_mode & NUMA_BALANCING_NORMAL) &&
> +                                   node_is_toptier(nid))
>                                         continue;
>                         }
>
> --
> 2.30.2
>