mm/swap: stop using page->private on tail pages for THP_SWAP

Patch series "mm/swap: stop using page->private on tail pages for THP_SWAP
+ cleanups".

This series stops using page->private on tail pages for THP_SWAP, replaces
folio->private by folio->swap for swapcache folios, and starts using
"new_folio" for tail pages that we are splitting to remove the usage of
page->private for swapcache handling completely.


This patch (of 4):

Let's stop using page->private on tail pages, making it possible to just
unconditionally reuse that field in the tail pages of large folios.

The remaining usage of the private field for THP_SWAP is in the THP
splitting code (mm/huge_memory.c), that we'll handle separately later.

Update the THP_SWAP documentation and sanity checks in mm_types.h and
__split_huge_page_tail().

[david@redhat.com: stop using page->private on tail pages for THP_SWAP]
  Link: https://lkml.kernel.org/r/6f0a82a3-6948-20d9-580b-be1dbf415701@redhat.com
Link: https://lkml.kernel.org/r/20230821160849.531668-1-david@redhat.com
Link: https://lkml.kernel.org/r/20230821160849.531668-2-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>	[arm64]
Reviewed-by: Yosry Ahmed <yosryahmed@google.com>
Cc: Dan Streetman <ddstreet@ieee.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Peter Xu <peterx@redhat.com>
Cc: Seth Jennings <sjenning@redhat.com>
Cc: Vitaly Wool <vitaly.wool@konsulko.com>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 1 insertions, 1 deletions

diff --git a/mm/rmap.c b/mm/rmap.c
index 1f04debdc87a..ec7f8e6c9e48 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1647,7 +1647,7 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
 			 */
 			dec_mm_counter(mm, mm_counter(&folio->page));
 		} else if (folio_test_anon(folio)) {
-			swp_entry_t entry = { .val = page_private(subpage) };
+			swp_entry_t entry = page_swap_entry(subpage);
 			pte_t swp_pte;
 			/*
 			 * Store the swap location in the pte.