6.6-stable review patch. If anyone has any objections, please let me know.
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From: Mel Gorman mgorman@techsingularity.net
[ Upstream commit b7a5b537c55c088d891ae554103d1b281abef781 ]
NUMA Balancing skips VMAs when the current task has not trapped a NUMA fault within the VMA. If the VMA is skipped then mm->numa_scan_offset advances and a task that is trapping faults within the VMA may never fully update PTEs within the VMA.
Force tasks to update PTEs for partially scanned PTEs. The VMA will be tagged for NUMA hints by some task but this removes some of the benefit of tracking PID activity within a VMA. A follow-on patch will mitigate this problem.
The test cases and machines evaluated did not trigger the corner case so the performance results are neutral with only small changes within the noise from normal test-to-test variance. However, the next patch makes the corner case easier to trigger.
Signed-off-by: Mel Gorman mgorman@techsingularity.net Signed-off-by: Ingo Molnar mingo@kernel.org Tested-by: Raghavendra K T raghavendra.kt@amd.com Link: https://lore.kernel.org/r/20231010083143.19593-6-mgorman@techsingularity.net Stable-dep-of: f22cde4371f3 ("sched/numa: Fix the vma scan starving issue") Signed-off-by: Sasha Levin sashal@kernel.org --- include/linux/sched/numa_balancing.h | 1 + include/trace/events/sched.h | 3 ++- kernel/sched/fair.c | 18 +++++++++++++++--- 3 files changed, 18 insertions(+), 4 deletions(-)
diff --git a/include/linux/sched/numa_balancing.h b/include/linux/sched/numa_balancing.h index c127a1509e2fa..7dcc0bdfddbbf 100644 --- a/include/linux/sched/numa_balancing.h +++ b/include/linux/sched/numa_balancing.h @@ -21,6 +21,7 @@ enum numa_vmaskip_reason { NUMAB_SKIP_INACCESSIBLE, NUMAB_SKIP_SCAN_DELAY, NUMAB_SKIP_PID_INACTIVE, + NUMAB_SKIP_IGNORE_PID, };
#ifdef CONFIG_NUMA_BALANCING diff --git a/include/trace/events/sched.h b/include/trace/events/sched.h index b0d0dbf491ea6..27b51c81b1067 100644 --- a/include/trace/events/sched.h +++ b/include/trace/events/sched.h @@ -670,7 +670,8 @@ DEFINE_EVENT(sched_numa_pair_template, sched_swap_numa, EM( NUMAB_SKIP_SHARED_RO, "shared_ro" ) \ EM( NUMAB_SKIP_INACCESSIBLE, "inaccessible" ) \ EM( NUMAB_SKIP_SCAN_DELAY, "scan_delay" ) \ - EMe(NUMAB_SKIP_PID_INACTIVE, "pid_inactive" ) + EM( NUMAB_SKIP_PID_INACTIVE, "pid_inactive" ) \ + EMe(NUMAB_SKIP_IGNORE_PID, "ignore_pid_inactive" )
/* Redefine for export. */ #undef EM diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 07363b73ccdcc..03eb1cab320d8 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -3188,7 +3188,7 @@ 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) +static bool vma_is_accessed(struct mm_struct *mm, struct vm_area_struct *vma) { unsigned long pids; /* @@ -3201,7 +3201,19 @@ static bool vma_is_accessed(struct vm_area_struct *vma) return true;
pids = vma->numab_state->pids_active[0] | vma->numab_state->pids_active[1]; - return test_bit(hash_32(current->pid, ilog2(BITS_PER_LONG)), &pids); + if (test_bit(hash_32(current->pid, ilog2(BITS_PER_LONG)), &pids)) + return true; + + /* + * Complete a scan that has already started regardless of PID access, or + * some VMAs may never be scanned in multi-threaded applications: + */ + if (mm->numa_scan_offset > vma->vm_start) { + trace_sched_skip_vma_numa(mm, vma, NUMAB_SKIP_IGNORE_PID); + return true; + } + + return false; }
#define VMA_PID_RESET_PERIOD (4 * sysctl_numa_balancing_scan_delay) @@ -3345,7 +3357,7 @@ static void task_numa_work(struct callback_head *work) }
/* Do not scan the VMA if task has not accessed */ - if (!vma_is_accessed(vma)) { + if (!vma_is_accessed(mm, vma)) { trace_sched_skip_vma_numa(mm, vma, NUMAB_SKIP_PID_INACTIVE); continue; }