On Tue, Mar 1, 2022 at 12:54 AM Huang Ying <ying.huang@xxxxxxxxx> 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@xxxxxxxxx>
>
> Signed-off-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
> Suggested-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
> Tested-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
> Reviewed-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
> Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>
> Reviewed-by: Oscar Salvador <osalvador@xxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxxx>
> Cc: Rik van Riel <riel@xxxxxxxxxxx>
> Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Yang Shi <shy828301@xxxxxxxxx>
> Cc: Zi Yan <ziy@xxxxxxxxxx>
> Cc: Wei Xu <weixugc@xxxxxxxxxx>
> Cc: Shakeel Butt <shakeelb@xxxxxxxxxx>
> Cc: zhongjiang-ali <zhongjiang-ali@xxxxxxxxxxxxxxxxx>
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> Cc: linux-mm@xxxxxxxxx
> ---
> 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
>
