Hi,
On Mon, Jan 16, 2023 at 07:05:34AM +0530, Raghavendra K T wrote:
> During the Numa scanning make sure only relevant vmas of the
> tasks are scanned.
Please add more detailed description about what are the issues with the
current scanning this patch aims to solve.
> Logic:
> 1) For the first two time allow unconditional scanning of vmas
> 2) Store recent 4 unique tasks (last 8bits of PIDs) accessed the vma.
> False negetives in case of collison should be fine here.
^ negatives
> 3) If more than 4 pids exist assume task indeed accessed vma to
> to avoid false negetives
>
> Co-developed-by: Bharata B Rao <bharata@xxxxxxx>
> (initial patch to store pid information)
>
> Suggested-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Bharata B Rao <bharata@xxxxxxx>
> Signed-off-by: Raghavendra K T <raghavendra.kt@xxxxxxx>
> ---
> include/linux/mm_types.h | 2 ++
> kernel/sched/fair.c | 32 ++++++++++++++++++++++++++++++++
> mm/memory.c | 21 +++++++++++++++++++++
> 3 files changed, 55 insertions(+)
>
> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> index 500e536796ca..07feae37b8e6 100644
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -506,6 +506,8 @@ struct vm_area_struct {
> struct mempolicy *vm_policy; /* NUMA policy for the VMA */
> #endif
> struct vm_userfaultfd_ctx vm_userfaultfd_ctx;
> + unsigned int accessing_pids;
> + int next_pid_slot;
> } __randomize_layout;
>
> struct kioctx_table;
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index e4a0b8bd941c..944d2e3b0b3c 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -2916,6 +2916,35 @@ static void reset_ptenuma_scan(struct task_struct *p)
> p->mm->numa_scan_offset = 0;
> }
>
> +static bool vma_is_accessed(struct vm_area_struct *vma)
> +{
> + int i;
> + bool more_pids_exist;
> + unsigned long pid, max_pids;
> + unsigned long current_pid = current->pid & LAST__PID_MASK;
> +
> + max_pids = sizeof(unsigned int) * BITS_PER_BYTE / LAST__PID_SHIFT;
> +
> + /* By default we assume >= max_pids exist */
> + more_pids_exist = true;
> +
> + if (READ_ONCE(current->mm->numa_scan_seq) < 2)
> + return true;
> +
> + for (i = 0; i < max_pids; i++) {
> + pid = (vma->accessing_pids >> i * LAST__PID_SHIFT) &
> + LAST__PID_MASK;
> + if (pid == current_pid)
> + return true;
> + if (pid == 0) {
> + more_pids_exist = false;
> + break;
> + }
> + }
> +
> + return more_pids_exist;
> +}
> +
> /*
> * The expensive part of numa migration is done from task_work context.
> * Triggered from task_tick_numa().
> @@ -3015,6 +3044,9 @@ static void task_numa_work(struct callback_head *work)
> if (!vma_is_accessible(vma))
> continue;
>
> + if (!vma_is_accessed(vma))
> + continue;
> +
> do {
> start = max(start, vma->vm_start);
> end = ALIGN(start + (pages << PAGE_SHIFT), HPAGE_SIZE);
> diff --git a/mm/memory.c b/mm/memory.c
> index 8c8420934d60..fafd78d87a51 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -4717,7 +4717,28 @@ static vm_fault_t do_numa_page(struct vm_fault *vmf)
> pte_t pte, old_pte;
> bool was_writable = pte_savedwrite(vmf->orig_pte);
> int flags = 0;
> + int pid_slot = vma->next_pid_slot;
>
> + int i;
> + unsigned long pid, max_pids;
> + unsigned long current_pid = current->pid & LAST__PID_MASK;
> +
> + max_pids = sizeof(unsigned int) * BITS_PER_BYTE / LAST__PID_SHIFT;
> +
> + /* Avoid duplicate PID updation */
> + for (i = 0; i < max_pids; i++) {
> + pid = (vma->accessing_pids >> i * LAST__PID_SHIFT) &
> + LAST__PID_MASK;
> + if (pid == current_pid)
> + goto skip_update;
> + }
> +
> + vma->next_pid_slot = (++pid_slot) % max_pids;
> + vma->accessing_pids &= ~(LAST__PID_MASK << (pid_slot * LAST__PID_SHIFT));
> + vma->accessing_pids |= ((current_pid) <<
> + (pid_slot * LAST__PID_SHIFT));
> +
> +skip_update:
> /*
> * The "pte" at this point cannot be used safely without
> * validation through pte_unmap_same(). It's of NUMA type but
> --
> 2.34.1
>
>
--
Sincerely yours,
Mike.
