mm, swap: simplify the code and reduce indention

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

No behavior change.

Link: https://lkml.kernel.org/r/20251220-swap-table-p2-v5-5-8862a265a033@tencent.com
Signed-off-by: Kairui Song <kasong@tencent.com>
Reviewed-by: Baoquan He <bhe@redhat.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Chris Li <chrisl@kernel.org>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Rafael J. Wysocki (Intel) <rafael@kernel.org>
Cc: Yosry Ahmed <yosry.ahmed@linux.dev>
Cc: Deepanshu Kartikey <kartikey406@gmail.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Kairui Song <ryncsn@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 43 insertions, 46 deletions

diff --git a/mm/memory.c b/mm/memory.c
index 6cbee2838ef7..8e38d3d93433 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -4767,55 +4767,52 @@ 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);
 
 	/*
@@ -5005,7 +5002,7 @@ check_folio:
 			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
@@ -5043,7 +5040,7 @@ out_page:
 	folio_unlock(folio);
 out_release:
 	folio_put(folio);
-	if (folio != swapcache && swapcache) {
+	if (folio != swapcache) {
 		folio_unlock(swapcache);
 		folio_put(swapcache);
 	}