| Message ID | 9c9c2d1b15e37f6e6bf32f99e3100035e90c4ac9.1588868430.git.sandipan@linux.ibm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v2] mm: Reset numa stats for boot pagesets | expand |
On 5/7/20 6:29 PM, Sandipan Das wrote: > Initially, the per-cpu pagesets of each zone are set to the > boot pagesets. The real pagesets are allocated later but > before that happens, page allocations do occur and the numa > stats for the boot pagesets get incremented since they are > common to all zones at that point. > > The real pagesets, however, are allocated for the populated > zones only. Unpopulated zones, like those associated with > memory-less nodes, continue using the boot pageset and end > up skewing the numa stats of the corresponding node. > > E.g. > > $ numactl -H > available: 2 nodes (0-1) > node 0 cpus: 0 1 2 3 > node 0 size: 0 MB > node 0 free: 0 MB > node 1 cpus: 4 5 6 7 > node 1 size: 8131 MB > node 1 free: 6980 MB > node distances: > node 0 1 > 0: 10 40 > 1: 40 10 > > $ numastat > node0 node1 > numa_hit 108 56495 > numa_miss 0 0 > numa_foreign 0 0 > interleave_hit 0 4537 > local_node 108 31547 > other_node 0 24948 > > Hence, the boot pageset stats need to be cleared after > the real pagesets are allocated. > > From this point onwards, the stats of the boot pagesets do > not change as page allocations requested for a memory-less > node will either fail (if __GFP_THISNODE is used) or get > fulfilled by a preferred zone of a different node based on > the fallback zonelist. > > Signed-off-by: Sandipan Das <sandipan@linux.ibm.com> Acked-by: Vlastimil Babka <vbabka@suse.cz> With suggestion below. > --- > > The previous version and discussion around it can be found at > https://lore.kernel.org/linux-mm/20200504070304.127361-1-sandipan@linux.ibm.com/ > > Changes in v2: > > - Reset the stats of the boot pagesets instead of explicitly > returning zero as suggested by Vlastimil. > > - Changed the subject to reflect the above. > > --- > mm/page_alloc.c | 19 +++++++++++++++++++ > 1 file changed, 19 insertions(+) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 69827d4fa052..1543e32f7e4e 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -6256,6 +6256,25 @@ void __init setup_per_cpu_pageset(void) > for_each_populated_zone(zone) > setup_zone_pageset(zone); > > +#ifdef CONFIG_NUMA > + if (static_branch_likely(&vm_numa_stat_key)) { I would just remove this test and do it unconditionally, as the branch can be only disabled later in boot by a sysctl. > + struct per_cpu_pageset *pcp; > + int cpu; > + > + /* > + * Unpopulated zones continue using the boot pagesets. > + * The numa stats for these pagesets need to be reset. > + * Otherwise, they will end up skewing the stats of > + * the nodes these zones are associated with. > + */ > + for_each_possible_cpu(cpu) { > + pcp = &per_cpu(boot_pageset, cpu); > + memset(pcp->vm_numa_stat_diff, 0, > + sizeof(pcp->vm_numa_stat_diff)); > + } > + } > +#endif > + > for_each_online_pgdat(pgdat) > pgdat->per_cpu_nodestats = > alloc_percpu(struct per_cpu_nodestat); >
diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 69827d4fa052..1543e32f7e4e 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -6256,6 +6256,25 @@ void __init setup_per_cpu_pageset(void) for_each_populated_zone(zone) setup_zone_pageset(zone); +#ifdef CONFIG_NUMA + if (static_branch_likely(&vm_numa_stat_key)) { + struct per_cpu_pageset *pcp; + int cpu; + + /* + * Unpopulated zones continue using the boot pagesets. + * The numa stats for these pagesets need to be reset. + * Otherwise, they will end up skewing the stats of + * the nodes these zones are associated with. + */ + for_each_possible_cpu(cpu) { + pcp = &per_cpu(boot_pageset, cpu); + memset(pcp->vm_numa_stat_diff, 0, + sizeof(pcp->vm_numa_stat_diff)); + } + } +#endif + for_each_online_pgdat(pgdat) pgdat->per_cpu_nodestats = alloc_percpu(struct per_cpu_nodestat);
Initially, the per-cpu pagesets of each zone are set to the boot pagesets. The real pagesets are allocated later but before that happens, page allocations do occur and the numa stats for the boot pagesets get incremented since they are common to all zones at that point. The real pagesets, however, are allocated for the populated zones only. Unpopulated zones, like those associated with memory-less nodes, continue using the boot pageset and end up skewing the numa stats of the corresponding node. E.g. $ numactl -H available: 2 nodes (0-1) node 0 cpus: 0 1 2 3 node 0 size: 0 MB node 0 free: 0 MB node 1 cpus: 4 5 6 7 node 1 size: 8131 MB node 1 free: 6980 MB node distances: node 0 1 0: 10 40 1: 40 10 $ numastat node0 node1 numa_hit 108 56495 numa_miss 0 0 numa_foreign 0 0 interleave_hit 0 4537 local_node 108 31547 other_node 0 24948 Hence, the boot pageset stats need to be cleared after the real pagesets are allocated. From this point onwards, the stats of the boot pagesets do not change as page allocations requested for a memory-less node will either fail (if __GFP_THISNODE is used) or get fulfilled by a preferred zone of a different node based on the fallback zonelist. Signed-off-by: Sandipan Das <sandipan@linux.ibm.com> --- The previous version and discussion around it can be found at https://lore.kernel.org/linux-mm/20200504070304.127361-1-sandipan@linux.ibm.com/ Changes in v2: - Reset the stats of the boot pagesets instead of explicitly returning zero as suggested by Vlastimil. - Changed the subject to reflect the above. --- mm/page_alloc.c | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+)