linux-kernel - [PATCH v4 5/6] mm/zswap: cleanup zswap_writeback

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Message-Id: <20231213-zswap-dstmem-v4-5-f228b059dd89@bytedance.com>
Date: Tue, 26 Dec 2023 15:54:12 +0000
From: Chengming Zhou <zhouchengming@...edance.com>
To: Andrew Morton <akpm@...ux-foundation.org>, Seth Jennings <sjenning@...hat.com>, Johannes Weiner <hannes@...xchg.org>,
 Vitaly Wool <vitaly.wool@...sulko.com>, Nhat Pham <nphamcs@...il.com>, Chris Li <chriscli@...gle.com>,
 Yosry Ahmed <yosryahmed@...gle.com>, Dan Streetman <ddstreet@...e.org>
Cc: linux-kernel@...r.kernel.org, Chengming Zhou <zhouchengming@...edance.com>, linux-mm@...ck.org,
 Nhat Pham <nphamcs@...il.com>, Yosry Ahmed <yosryahmed@...gle.com>, Chris Li <chrisl@...nel.org>
Subject: [PATCH v4 5/6] mm/zswap: cleanup zswap_writeback_entry()

Also after the common decompress part goes to __zswap_load(), we can
cleanup the zswap_writeback_entry() a little.

Reviewed-by: Yosry Ahmed <yosryahmed@...gle.com>
Reviewed-by: Nhat Pham <nphamcs@...il.com>
Acked-by: Chris Li <chrisl@...nel.org> (Google)
Signed-off-by: Chengming Zhou <zhouchengming@...edance.com>
---
 mm/zswap.c | 29 ++++++++++-------------------
 1 file changed, 10 insertions(+), 19 deletions(-)

diff --git a/mm/zswap.c b/mm/zswap.c
index 86886276cb81..40ee9f109f98 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -1443,7 +1443,6 @@ static int zswap_writeback_entry(struct zswap_entry *entry,
 	struct page *page;
 	struct mempolicy *mpol;
 	bool page_was_allocated;
-	int ret;
 	struct writeback_control wbc = {
 		.sync_mode = WB_SYNC_NONE,
 	};
@@ -1452,16 +1451,17 @@ static int zswap_writeback_entry(struct zswap_entry *entry,
 	mpol = get_task_policy(current);
 	page = __read_swap_cache_async(swpentry, GFP_KERNEL, mpol,
 				NO_INTERLEAVE_INDEX, &page_was_allocated, true);
-	if (!page) {
-		ret = -ENOMEM;
-		goto fail;
-	}
+	if (!page)
+		return -ENOMEM;
 
-	/* Found an existing page, we raced with load/swapin */
+	/*
+	 * Found an existing page, we raced with load/swapin. We generally
+	 * writeback cold pages from zswap, and swapin means the page just
+	 * became hot. Skip this page and let the caller find another one.
+	 */
 	if (!page_was_allocated) {
 		put_page(page);
-		ret = -EEXIST;
-		goto fail;
+		return -EEXIST;
 	}
 
 	/*
@@ -1475,8 +1475,7 @@ static int zswap_writeback_entry(struct zswap_entry *entry,
 	if (zswap_rb_search(&tree->rbroot, swp_offset(entry->swpentry)) != entry) {
 		spin_unlock(&tree->lock);
 		delete_from_swap_cache(page_folio(page));
-		ret = -ENOMEM;
-		goto fail;
+		return -ENOMEM;
 	}
 	spin_unlock(&tree->lock);
 
@@ -1497,15 +1496,7 @@ static int zswap_writeback_entry(struct zswap_entry *entry,
 	__swap_writepage(page, &wbc);
 	put_page(page);
 
-	return ret;
-
-fail:
-	/*
-	 * If we get here because the page is already in swapcache, a
-	 * load may be happening concurrently. It is safe and okay to
-	 * not free the entry. It is also okay to return !0.
-	 */
-	return ret;
+	return 0;
 }
 
 static int zswap_is_page_same_filled(void *ptr, unsigned long *value)

-- 
b4 0.10.1