[PATCH v4 05/19] mm, swap: simplify the code and reduce indention

Kairui Song
2025-12-04T19:30:06Z

Now swap cache is always used, multiple swap cache checks are no longer
useful, remove them and reduce the code indention.

No behavior change.

Signed-off-by: Kairui Song <kasong@tencent.com>
---
mm/memory.c | 89 +++++++++++++++++++++++++++++--------------------------------
1 file changed, 43 insertions(+), 46 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index 9fb2032772f2..3f707275d540 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -4764,55 +4764,52 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
goto out_release;

page = folio_file_page(folio, swp_offset(entry));
- if (swapcache) {
- /*
- * Make sure folio_free_swap() or swapoff did not release the
- * swapcache from under us. The page pin, and pte_same test
- * below, are not enough to exclude that. Even if it is still
- * swapcache, we need to check that the page's swap has not
- * changed.
- */
- if (unlikely(!folio_matches_swap_entry(folio, entry)))
- goto out_page;
-
- if (unlikely(PageHWPoison(page))) {
- /*
- * hwpoisoned dirty swapcache pages are kept for killing
- * owner processes (which may be unknown at hwpoison time)
- */
- ret = VM_FAULT_HWPOISON;
- goto out_page;
- }
-
- /*
- * KSM sometimes has to copy on read faults, for example, if
- * folio->index of non-ksm folios would be nonlinear inside the
- * anon VMA -- the ksm flag is lost on actual swapout.
- */
- folio = ksm_might_need_to_copy(folio, vma, vmf->address);
- if (unlikely(!folio)) {
- ret = VM_FAULT_OOM;
- folio = swapcache;
- goto out_page;
- } else if (unlikely(folio == ERR_PTR(-EHWPOISON))) {
- ret = VM_FAULT_HWPOISON;
- folio = swapcache;
- goto out_page;
- }
- if (folio != swapcache)
- page = folio_page(folio, 0);
+ /*
+ * Make sure folio_free_swap() or swapoff did not release the
+ * swapcache from under us. The page pin, and pte_same test
+ * below, are not enough to exclude that. Even if it is still
+ * swapcache, we need to check that the page's swap has not
+ * changed.
+ */
+ if (unlikely(!folio_matches_swap_entry(folio, entry)))
+ goto out_page;

+ if (unlikely(PageHWPoison(page))) {
/*
- * If we want to map a page that's in the swapcache writable, we
- * have to detect via the refcount if we're really the exclusive
- * owner. Try removing the extra reference from the local LRU
- * caches if required.
+ * hwpoisoned dirty swapcache pages are kept for killing
+ * owner processes (which may be unknown at hwpoison time)
*/
- if ((vmf->flags & FAULT_FLAG_WRITE) && folio == swapcache &&
- !folio_test_ksm(folio) && !folio_test_lru(folio))
- lru_add_drain();
+ ret = VM_FAULT_HWPOISON;
+ goto out_page;
}

+ /*
+ * KSM sometimes has to copy on read faults, for example, if
+ * folio->index of non-ksm folios would be nonlinear inside the
+ * anon VMA -- the ksm flag is lost on actual swapout.
+ */
+ folio = ksm_might_need_to_copy(folio, vma, vmf->address);
+ if (unlikely(!folio)) {
+ ret = VM_FAULT_OOM;
+ folio = swapcache;
+ goto out_page;
+ } else if (unlikely(folio == ERR_PTR(-EHWPOISON))) {
+ ret = VM_FAULT_HWPOISON;
+ folio = swapcache;
+ goto out_page;
+ } else if (folio != swapcache)
+ page = folio_page(folio, 0);
+
+ /*
+ * If we want to map a page that's in the swapcache writable, we
+ * have to detect via the refcount if we're really the exclusive
+ * owner. Try removing the extra reference from the local LRU
+ * caches if required.
+ */
+ if ((vmf->flags & FAULT_FLAG_WRITE) &&
+ !folio_test_ksm(folio) && !folio_test_lru(folio))
+ lru_add_drain();
+
folio_throttle_swaprate(folio, GFP_KERNEL);

/*
@@ -5002,7 +4999,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
pte, pte, nr_pages);

folio_unlock(folio);
- if (folio != swapcache && swapcache) {
+ if (unlikely(folio != swapcache)) {
/*
* Hold the lock to avoid the swap entry to be reused
* until we take the PT lock for the pte_same() check
@@ -5040,7 +5037,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
folio_unlock(folio);
out_release:
folio_put(folio);
- if (folio != swapcache && swapcache) {
+ if (folio != swapcache) {
folio_unlock(swapcache);
folio_put(swapcache);
}

--
2.52.0