mm: swap: free_swap_and_cache_nr() as batched free_swap_and_cache()

Now that we no longer have a convenient flag in the cluster to determine
if a folio is large, free_swap_and_cache() will take a reference and lock
a large folio much more often, which could lead to contention and (e.g.)
failure to split large folios, etc.

Let's solve that problem by batch freeing swap and cache with a new
function, free_swap_and_cache_nr(), to free a contiguous range of swap
entries together.  This allows us to first drop a reference to each swap
slot before we try to release the cache folio.  This means we only try to
release the folio once, only taking the reference and lock once - much
better than the previous 512 times for the 2M THP case.

Contiguous swap entries are gathered in zap_pte_range() and
madvise_free_pte_range() in a similar way to how present ptes are already
gathered in zap_pte_range().

While we are at it, let's simplify by converting the return type of both
functions to void.  The return value was used only by zap_pte_range() to
print a bad pte, and was ignored by everyone else, so the extra reporting
wasn't exactly guaranteed.  We will still get the warning with most of the
information from get_swap_device().  With the batch version, we wouldn't
know which pte was bad anyway so could print the wrong one.

[ryan.roberts@arm.com: fix a build warning on parisc]
  Link: https://lkml.kernel.org/r/20240409111840.3173122-1-ryan.roberts@arm.com
Link: https://lkml.kernel.org/r/20240408183946.2991168-3-ryan.roberts@arm.com
Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Barry Song <21cnbao@gmail.com>
Cc: Barry Song <v-songbaohua@oppo.com>
Cc: Chris Li <chrisl@kernel.org>
Cc: Gao Xiang <xiang@kernel.org>
Cc: "Huang, Ying" <ying.huang@intel.com>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Lance Yang <ioworker0@gmail.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Yang Shi <shy828301@gmail.com>
Cc: Yu Zhao <yuzhao@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 7 insertions, 6 deletions

diff --git a/mm/memory.c b/mm/memory.c
index 694e18837cd8..7880400370c8 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1637,12 +1637,13 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb,
 				folio_remove_rmap_pte(folio, page, vma);
 			folio_put(folio);
 		} else if (!non_swap_entry(entry)) {
-			/* Genuine swap entry, hence a private anon page */
+			max_nr = (end - addr) / PAGE_SIZE;
+			nr = swap_pte_batch(pte, max_nr, ptent);
+			/* Genuine swap entries, hence a private anon pages */
 			if (!should_zap_cows(details))
 				continue;
-			rss[MM_SWAPENTS]--;
-			if (unlikely(!free_swap_and_cache(entry)))
-				print_bad_pte(vma, addr, ptent, NULL);
+			rss[MM_SWAPENTS] -= nr;
+			free_swap_and_cache_nr(entry, nr);
 		} else if (is_migration_entry(entry)) {
 			folio = pfn_swap_entry_folio(entry);
 			if (!should_zap_folio(details, folio))
@@ -1665,8 +1666,8 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb,
 			pr_alert("unrecognized swap entry 0x%lx\n", entry.val);
 			WARN_ON_ONCE(1);
 		}
-		pte_clear_not_present_full(mm, addr, pte, tlb->fullmm);
-		zap_install_uffd_wp_if_needed(vma, addr, pte, 1, details, ptent);
+		clear_not_present_full_ptes(mm, addr, pte, nr, tlb->fullmm);
+		zap_install_uffd_wp_if_needed(vma, addr, pte, nr, details, ptent);
 	} while (pte += nr, addr += PAGE_SIZE * nr, addr != end);
 
 	add_mm_rss_vec(mm, rss);