linux-kernel - Re: [PATCH] mm/swapfile: move scan_swap_map() under CONFIG

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Date:   Mon, 24 May 2021 13:06:52 +0100
From:   Christoph Hellwig <hch@...radead.org>
To:     Miaohe Lin <linmiaohe@...wei.com>
Cc:     akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [PATCH] mm/swapfile: move scan_swap_map() under
 CONFIG_HIBERNATION

Please just fold it into the only caller and update the comments
referring to it.  Something like:

diff --git a/mm/swapfile.c b/mm/swapfile.c
index 149e77454e3c..0e575b45bb87 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -452,10 +452,10 @@ static void swap_cluster_schedule_discard(struct swap_info_struct *si,
 		unsigned int idx)
 {
 	/*
-	 * If scan_swap_map() can't find a free cluster, it will check
+	 * If scan_swap_map_slots() can't find a free cluster, it will check
 	 * si->swap_map directly. To make sure the discarding cluster isn't
-	 * taken by scan_swap_map(), mark the swap entries bad (occupied). It
-	 * will be cleared after discard
+	 * taken by scan_swap_map_slots(), mark the swap entries bad (occupied).
+	 * It will be cleared after discard
 	 */
 	memset(si->swap_map + idx * SWAPFILE_CLUSTER,
 			SWAP_MAP_BAD, SWAPFILE_CLUSTER);
@@ -580,7 +580,7 @@ static void dec_cluster_info_page(struct swap_info_struct *p,
 }
 
 /*
- * It's possible scan_swap_map() uses a free cluster in the middle of free
+ * It's possible scan_swap_map_slots() uses a free cluster in the middle of free
  * cluster list. Avoiding such abuse to avoid list corruption.
  */
 static bool
@@ -1028,21 +1028,6 @@ static void swap_free_cluster(struct swap_info_struct *si, unsigned long idx)
 	swap_range_free(si, offset, SWAPFILE_CLUSTER);
 }
 
-static unsigned long scan_swap_map(struct swap_info_struct *si,
-				   unsigned char usage)
-{
-	swp_entry_t entry;
-	int n_ret;
-
-	n_ret = scan_swap_map_slots(si, usage, 1, &entry);
-
-	if (n_ret)
-		return swp_offset(entry);
-	else
-		return 0;
-
-}
-
 int get_swap_pages(int n_goal, swp_entry_t swp_entries[], int entry_size)
 {
 	unsigned long size = swap_entry_size(entry_size);
@@ -1105,14 +1090,14 @@ int get_swap_pages(int n_goal, swp_entry_t swp_entries[], int entry_size)
 nextsi:
 		/*
 		 * if we got here, it's likely that si was almost full before,
-		 * and since scan_swap_map() can drop the si->lock, multiple
-		 * callers probably all tried to get a page from the same si
-		 * and it filled up before we could get one; or, the si filled
-		 * up between us dropping swap_avail_lock and taking si->lock.
-		 * Since we dropped the swap_avail_lock, the swap_avail_head
-		 * list may have been modified; so if next is still in the
-		 * swap_avail_head list then try it, otherwise start over
-		 * if we have not gotten any slots.
+		 * and since scan_swap_map_slots() can drop the si->lock,
+		 * multiple callers probably all tried to get a page from the
+		 * same si and it filled up before we could get one; or, the si
+		 * filled up between us dropping swap_avail_lock and taking
+		 * si->lock.  Since we dropped the swap_avail_lock, the
+		 * swap_avail_head list may have been modified; so if next is
+		 * still in the swap_avail_head list then try it, otherwise
+		 * start over if we have not gotten any slots.
 		 */
 		if (plist_node_empty(&next->avail_lists[node]))
 			goto start_over;
@@ -1132,24 +1117,18 @@ int get_swap_pages(int n_goal, swp_entry_t swp_entries[], int entry_size)
 swp_entry_t get_swap_page_of_type(int type)
 {
 	struct swap_info_struct *si = swap_type_to_swap_info(type);
-	pgoff_t offset;
+	swp_entry_t entry = { };
 
 	if (!si)
 		goto fail;
 
+	/* This is called for allocating swap entry, not cache */
 	spin_lock(&si->lock);
-	if (si->flags & SWP_WRITEOK) {
-		/* This is called for allocating swap entry, not cache */
-		offset = scan_swap_map(si, 1);
-		if (offset) {
-			atomic_long_dec(&nr_swap_pages);
-			spin_unlock(&si->lock);
-			return swp_entry(type, offset);
-		}
-	}
+	if ((si->flags & SWP_WRITEOK) && scan_swap_map_slots(si, 1, 1, &entry))
+		atomic_long_dec(&nr_swap_pages);
 	spin_unlock(&si->lock);
 fail:
-	return (swp_entry_t) {0};
+	return entry;
 }
 
 static struct swap_info_struct *__swap_info_get(swp_entry_t entry)