On 20 Jun 2024, at 17:29, David Hildenbrand wrote: > Currently we always take a folio reference even if migration will not > even be tried or isolation failed, requiring us to grab+drop an additional > reference. > > Further, we end up calling folio_likely_mapped_shared() while the folio > might have already been unmapped, because after we dropped the PTL, that > can easily happen. We want to stop touching mapcounts and friends from > such context, and only call folio_likely_mapped_shared() while the folio > is still mapped: mapcount information is pretty much stale and unreliable > otherwise. > > So let's move checks into numamigrate_isolate_folio(), rename that > function to migrate_misplaced_folio_prepare(), and call that function > from callsites where we call migrate_misplaced_folio(), but still with > the PTL held. > > We can now stop taking temporary folio references, and really only take > a reference if folio isolation succeeded. Doing the > folio_likely_mapped_shared() + golio isolation under PT lock is now similar > to how we handle MADV_PAGEOUT. > > While at it, combine the folio_is_file_lru() checks. > > Signed-off-by: David Hildenbrand <david@xxxxxxxxxx> > --- > include/linux/migrate.h | 7 ++++ > mm/huge_memory.c | 8 ++-- > mm/memory.c | 9 +++-- > mm/migrate.c | 81 +++++++++++++++++++---------------------- > 4 files changed, 55 insertions(+), 50 deletions(-) > > diff --git a/include/linux/migrate.h b/include/linux/migrate.h > index f9d92482d117..644be30b69c8 100644 > --- a/include/linux/migrate.h > +++ b/include/linux/migrate.h > @@ -139,9 +139,16 @@ const struct movable_operations *page_movable_ops(struct page *page) > } > > #ifdef CONFIG_NUMA_BALANCING > +int migrate_misplaced_folio_prepare(struct folio *folio, > + struct vm_area_struct *vma, int node); > int migrate_misplaced_folio(struct folio *folio, struct vm_area_struct *vma, > int node); > #else > +static inline int migrate_misplaced_folio_prepare(struct folio *folio, > + struct vm_area_struct *vma, int node) > +{ > + return -EAGAIN; /* can't migrate now */ > +} > static inline int migrate_misplaced_folio(struct folio *folio, > struct vm_area_struct *vma, int node) > { > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index fc27dabcd8e3..4b2817bb2c7d 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -1688,11 +1688,13 @@ vm_fault_t do_huge_pmd_numa_page(struct vm_fault *vmf) > if (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) { > - folio_put(folio); > + if (target_nid == NUMA_NO_NODE) > + goto out_map; > + if (migrate_misplaced_folio_prepare(folio, vma, target_nid)) { > + flags |= TNF_MIGRATE_FAIL; > goto out_map; > } > - > + /* The folio is isolated and isolation code holds a folio reference. */ > spin_unlock(vmf->ptl); > writable = false; > > diff --git a/mm/memory.c b/mm/memory.c > index 118660de5bcc..4fd1ecfced4d 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -5207,8 +5207,6 @@ int numa_migrate_prep(struct folio *folio, struct vm_fault *vmf, > { > struct vm_area_struct *vma = vmf->vma; > > - folio_get(folio); > - > /* Record the current PID acceesing VMA */ > vma_set_access_pid_bit(vma); Without taking a reference here, is it safe to call mpol_misplaced() on the folio at the return? Can this folio be freed? -- Best Regards, Yan, Zi
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