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Date: Mon, 25 Mar 2024 23:50:10 +0000
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Subject: [RFC PATCH 2/9] mm: zswap: refactor storing to the tree out of zswap_store()
From: Yosry Ahmed <yosryahmed@google.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>, Nhat Pham <nphamcs@gmail.com>, 
	Chengming Zhou <chengming.zhou@linux.dev>, linux-mm@kvack.org, linux-kernel@vger.kernel.org, 
	Yosry Ahmed <yosryahmed@google.com>
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Refactor the code that attempts storing to the xarray, handling erros,
and freeing stale entries into a helper. This will be reused in a
following patch to free other types of tree elements as well.

Signed-off-by: Yosry Ahmed <yosryahmed@google.com>
---
 mm/zswap.c | 42 ++++++++++++++++++++++++++----------------
 1 file changed, 26 insertions(+), 16 deletions(-)

diff --git a/mm/zswap.c b/mm/zswap.c
index 1cf3ab4b22e64..ff1975afb7e3d 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -827,6 +827,30 @@ static void zswap_entry_free(struct zswap_entry *entry)
 	atomic_dec(&zswap_stored_pages);
 }
 
+/*********************************
+* zswap tree functions
+**********************************/
+static int zswap_tree_store(struct xarray *tree, pgoff_t offset, void *new)
+{
+	void *old;
+	int err;
+
+	old = xa_store(tree, offset, new, GFP_KERNEL);
+	err = xa_is_err(old);
+	if (err) {
+		WARN_ONCE(err != -ENOMEM, "unexpected xarray error: %d\n", err);
+		zswap_reject_alloc_fail++;
+	} else if (old) {
+		/*
+		 * We may have had an existing entry that became stale when
+		 * the folio was redirtied and now the new version is being
+		 * swapped out. Get rid of the old.
+		 */
+		zswap_entry_free(old);
+	}
+	return err;
+}
+
 /*********************************
 * compressed storage functions
 **********************************/
@@ -1396,10 +1420,10 @@ bool zswap_store(struct folio *folio)
 	swp_entry_t swp = folio->swap;
 	pgoff_t offset = swp_offset(swp);
 	struct xarray *tree = swap_zswap_tree(swp);
-	struct zswap_entry *entry, *old;
 	struct obj_cgroup *objcg = NULL;
 	struct mem_cgroup *memcg = NULL;
 	unsigned long max_pages, cur_pages;
+	struct zswap_entry *entry;
 
 	VM_WARN_ON_ONCE(!folio_test_locked(folio));
 	VM_WARN_ON_ONCE(!folio_test_swapcache(folio));
@@ -1485,22 +1509,8 @@ bool zswap_store(struct folio *folio)
 	entry->swpentry = swp;
 	entry->objcg = objcg;
 
-	old = xa_store(tree, offset, entry, GFP_KERNEL);
-	if (xa_is_err(old)) {
-		int err = xa_err(old);
-
-		WARN_ONCE(err != -ENOMEM, "unexpected xarray error: %d\n", err);
-		zswap_reject_alloc_fail++;
+	if (zswap_tree_store(tree, offset, entry))
 		goto store_failed;
-	}
-
-	/*
-	 * We may have had an existing entry that became stale when
-	 * the folio was redirtied and now the new version is being
-	 * swapped out. Get rid of the old.
-	 */
-	if (old)
-		zswap_entry_free(old);
 
 	if (objcg) {
 		obj_cgroup_charge_zswap(objcg, entry->length);
-- 
2.44.0.396.g6e790dbe36-goog