Re: [PATCH v2 2/4] mm: migrate: move the numamigrate_isolate_page() into do_numa_page()

[Baolin Wang]

On 8/22/2023 5:02 PM, Bharata B Rao wrote:
> On 22-Aug-23 6:23 AM, Baolin Wang wrote:
> > Move the numamigrate_isolate_page() into do_numa_page() to simplify the
> > migrate_misplaced_page(), which now only focuses on page migration, and
> > it also serves as a preparation for supporting batch migration for
> > migrate_misplaced_page().
> >
> > While we are at it, change the numamigrate_isolate_page() to boolean
> > type to make the return value more clear.
> >
> > Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
> > ---
> >   include/linux/migrate.h |  6 ++++++
> >   mm/huge_memory.c        |  7 +++++++
> >   mm/memory.c             |  7 +++++++
> >   mm/migrate.c            | 22 +++++++---------------
> >   4 files changed, 27 insertions(+), 15 deletions(-)
> >
> > diff --git a/include/linux/migrate.h b/include/linux/migrate.h
> > index 711dd9412561..ddcd62ec2c12 100644
> > --- a/include/linux/migrate.h
> > +++ b/include/linux/migrate.h
> > @@ -144,12 +144,18 @@ const struct movable_operations *page_movable_ops(struct page *page)
> >   #ifdef CONFIG_NUMA_BALANCING
> >   int migrate_misplaced_page(struct page *page, struct vm_area_struct *vma,
> >   			   int node);
> > +bool numamigrate_isolate_page(pg_data_t *pgdat, struct page *page);
> >   #else
> >   static inline int migrate_misplaced_page(struct page *page,
> >   					 struct vm_area_struct *vma, int node)
> >   {
> >   	return -EAGAIN; /* can't migrate now */
> >   }
> > +
> > +static inline bool numamigrate_isolate_page(pg_data_t *pgdat, struct page *page)
> > +{
> > +	return false;
> > +}
> >   #endif /* CONFIG_NUMA_BALANCING */
> >   
> >   #ifdef CONFIG_MIGRATION
> > diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> > index 4a9b34a89854..07149ead11e4 100644
> > --- a/mm/huge_memory.c
> > +++ b/mm/huge_memory.c
> > @@ -1496,6 +1496,7 @@ vm_fault_t do_huge_pmd_numa_page(struct vm_fault *vmf)
> >   	int target_nid, last_cpupid = (-1 & LAST_CPUPID_MASK);
> >   	bool migrated = false, writable = false;
> >   	int flags = 0;
> > +	pg_data_t *pgdat;
> >   
> >   	vmf->ptl = pmd_lock(vma->vm_mm, vmf->pmd);
> >   	if (unlikely(!pmd_same(oldpmd, *vmf->pmd))) {
> > @@ -1545,6 +1546,12 @@ vm_fault_t do_huge_pmd_numa_page(struct vm_fault *vmf)
> >   		goto migrate_fail;
> >   	}
> >   
> > +	pgdat = NODE_DATA(target_nid);
> > +	if (!numamigrate_isolate_page(pgdat, page)) {
> > +		put_page(page);
> > +		goto migrate_fail;
> > +	}
> > +
> >   	migrated = migrate_misplaced_page(page, vma, target_nid);
> >   	if (migrated) {
> >   		flags |= TNF_MIGRATED;
> > diff --git a/mm/memory.c b/mm/memory.c
> > index fc6f6b7a70e1..4e451b041488 100644
> > --- a/mm/memory.c
> > +++ b/mm/memory.c
> > @@ -4769,6 +4769,7 @@ static vm_fault_t do_numa_page(struct vm_fault *vmf)
> >   	int target_nid;
> >   	pte_t pte, old_pte;
> >   	int flags = 0;
> > +	pg_data_t *pgdat;
> >   
> >   	/*
> >   	 * The "pte" at this point cannot be used safely without
> > @@ -4844,6 +4845,12 @@ static vm_fault_t do_numa_page(struct vm_fault *vmf)
> >   		goto migrate_fail;
> >   	}
> >   
> > +	pgdat = NODE_DATA(target_nid);
> > +	if (!numamigrate_isolate_page(pgdat, page)) {
> > +		put_page(page);
> > +		goto migrate_fail;
> > +	}
> > +
> >   	/* Migrate to the requested node */
> >   	if (migrate_misplaced_page(page, vma, target_nid)) {
> >   		page_nid = target_nid;
> > diff --git a/mm/migrate.c b/mm/migrate.c
> > index 9cc98fb1d6ec..0b2b69a2a7ab 100644
> > --- a/mm/migrate.c
> > +++ b/mm/migrate.c
> > @@ -2478,7 +2478,7 @@ static struct folio *alloc_misplaced_dst_folio(struct folio *src,
> >   	return __folio_alloc_node(gfp, order, nid);
> >   }
> >   
> > -static int numamigrate_isolate_page(pg_data_t *pgdat, struct page *page)
> > +bool numamigrate_isolate_page(pg_data_t *pgdat, struct page *page)
> >   {
> >   	int nr_pages = thp_nr_pages(page);
> >   	int order = compound_order(page);
> > @@ -2496,11 +2496,11 @@ static int numamigrate_isolate_page(pg_data_t *pgdat, struct page *page)
> >   				break;
> >   		}
>
> There is an other s/return 0/return false/ changed required here for this chunk:
>
> if (!(sysctl_numa_balancing_mode & NUMA_BALANCING_MEMORY_TIERING))
>                          return 0;

Good catch.

> >   		wakeup_kswapd(pgdat->node_zones + z, 0, order, ZONE_MOVABLE);
> > -		return 0;
> > +		return false;
> >   	}
>
> Looks like this whole section under "Avoiding migrating to a node that is nearly full"
> check could be moved to numa_page_can_migrate() as that can be considered as one more
> check (or action to) see if the page can be migrated or not. After that numamigrate_isolate_page()
> will truly be about isolating the page.

Good idea. Will do. Thanks.