Re: [RFC PATCH 1/3] memory tiering: read last_cpupid correctly in do_huge_pmd_numa_page()

[David Hildenbrand]

On 13.07.24 03:18, Zi Yan wrote:
> On 12 Jul 2024, at 21:13, David Hildenbrand wrote:
>
> > On 12.07.24 04:44, Zi Yan wrote:
> > > From: Zi Yan <ziy@xxxxxxxxxx>
> > >
> > > last_cpupid is only available when memory tiering is off or the folio
> > > is in toptier node. Complete the check to read last_cpupid when it is
> > > available.
> > >
> > > Before the fix, the default last_cpupid will be used even if memory
> > > tiering mode is turned off at runtime instead of the actual value. This
> > > can prevent task_numa_fault() from getting right numa fault stats, but
> > > should not cause any crash. User might see performance changes after the
> > > fix.
> > >
> > > Fixes: 33024536bafd ("memory tiering: hot page selection with hint page fault latency")
> > > Signed-off-by: Zi Yan <ziy@xxxxxxxxxx>
> > > ---
> > >    mm/huge_memory.c | 3 ++-
> > >    1 file changed, 2 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> > > index d7c84480f1a4..07d9dde4ca33 100644
> > > --- a/mm/huge_memory.c
> > > +++ b/mm/huge_memory.c
> > > @@ -1705,7 +1705,8 @@ vm_fault_t do_huge_pmd_numa_page(struct vm_fault *vmf)
> > >    	 * For memory tiering mode, cpupid of slow memory page is used
> > >    	 * to record page access time.  So use default value.
> > >    	 */
> > > -	if (node_is_toptier(nid))
> > > +	if (!(sysctl_numa_balancing_mode & NUMA_BALANCING_MEMORY_TIERING) ||
> > > +	    node_is_toptier(nid))
> > >    		last_cpupid = folio_last_cpupid(folio);
> > >    	target_nid = numa_migrate_prep(folio, vmf, haddr, nid, &flags);
> > >    	if (target_nid == NUMA_NO_NODE)
> >
> > Reported-by: ...
>
> Reported-by: David Hildenbrand <david@xxxxxxxxxx>
>
> I suppose your email[1] reports the issue based on code inspection.


Yes, thanks for taking care of the fix and cleanups!

--
Cheers,

David / dhildenb