[RFC PATCH 1/6] f2fs: generalize metadata cache shrinking to explicit lists

[Wenjie Qi]

The metadata-cache shrinker currently operates on cache->lru_list.
Node-cache compression needs separate raw and compressed queues, while
keeping the existing isolation, truncation and refcount rules.

Move the common shrink loop to f2fs_shrink_cache_list(), and pass it an
explicit list, population and scan budget. Existing caches continue to
use their current LRU lists.

Also return the number of examined entries for queue-specific reclaim
accounting.

Signed-off-by: Wenjie Qi <qiwenjie@xxxxxxxxxx>
---
 fs/f2fs/cache.c | 30 +++++++++++++++++++++---------
 fs/f2fs/cache.h |  6 +++++-
 2 files changed, 26 insertions(+), 10 deletions(-)

diff --git a/fs/f2fs/cache.c b/fs/f2fs/cache.c
index 38fc5eb17f92..8f81aed132ed 100644
--- a/fs/f2fs/cache.c
+++ b/fs/f2fs/cache.c
@@ -547,8 +547,10 @@ void f2fs_destroy_cache(struct f2fs_cached_block_list *cache)
 	goto next;
 }
 
-static unsigned long f2fs_do_shrink_cache(struct f2fs_cached_block_list *cache,
-						unsigned long nr_to_scan)
+unsigned long
+f2fs_shrink_cache_list(struct f2fs_cached_block_list *cache,
+		       struct list_head *head, unsigned long nr_entries,
+		       unsigned long nr_to_scan, unsigned long *nr_scanned)
 {
 	struct f2fs_cached_block *entry, *next;
 	LIST_HEAD(dispose_list);
@@ -558,15 +560,15 @@ static unsigned long f2fs_do_shrink_cache(struct f2fs_cached_block_list *cache,
 
 	/* Phase 1: Isolate candidate entries from LRU list into dispose_list */
 	spin_lock(&cache->list_lock);
-	list_for_each_entry_safe(entry, next, &cache->lru_list, list) {
-		if (scanned >= cache->num_entries)
-			break;
-		if (scanned++ >= nr_to_scan)
+	nr_entries = min(nr_entries, cache->num_entries);
+	list_for_each_entry_safe(entry, next, head, list) {
+		if (scanned >= nr_entries || scanned >= nr_to_scan)
 			break;
+		scanned++;
 
 		/* If accessed, give it a second chance to rotate to tail */
 		if (f2fs_cache_test_and_clear_referenced(entry)) {
-			list_move_tail(&entry->list, &cache->lru_list);
+			list_move_tail(&entry->list, head);
 			continue;
 		}
 
@@ -620,16 +622,26 @@ static unsigned long f2fs_do_shrink_cache(struct f2fs_cached_block_list *cache,
 			freed++;
 	}
 
-	/* Phase 3: Splice un-reclaimed entries back onto cache->lru_list */
+	/* Phase 3: Splice un-reclaimed entries back onto the scanned list */
 	if (!list_empty(&keep_list)) {
 		spin_lock(&cache->list_lock);
-		list_splice_tail(&keep_list, &cache->lru_list);
+		list_splice_tail(&keep_list, head);
 		spin_unlock(&cache->list_lock);
 	}
+	if (nr_scanned)
+		*nr_scanned = scanned;
 
 	return freed;
 }
 
+static unsigned long
+f2fs_do_shrink_cache(struct f2fs_cached_block_list *cache,
+		     unsigned long nr_to_scan)
+{
+	return f2fs_shrink_cache_list(cache, &cache->lru_list, ULONG_MAX,
+			nr_to_scan, NULL);
+}
+
 unsigned long f2fs_shrink_cache(struct f2fs_sb_info *sbi,
 					unsigned long nr_to_scan)
 {
diff --git a/fs/f2fs/cache.h b/fs/f2fs/cache.h
index 6c4db910d767..c4c3d09a0008 100644
--- a/fs/f2fs/cache.h
+++ b/fs/f2fs/cache.h
@@ -222,7 +222,11 @@ void f2fs_drop_cache_range(struct f2fs_cached_block_list *cache,
 	f2fs_drop_cache_range(NODE_CACHE(sbi), start, len, true)
 
 unsigned long f2fs_shrink_cache(struct f2fs_sb_info *sbi,
-				unsigned long nr_to_scan);
+					unsigned long nr_to_scan);
+unsigned long
+f2fs_shrink_cache_list(struct f2fs_cached_block_list *cache,
+		       struct list_head *head, unsigned long nr_entries,
+		       unsigned long nr_to_scan, unsigned long *nr_scanned);
 
 #define DEF_DIRTY_CACHE_TIMEOUT 5000
 #define MIN_DIRTY_CACHE_TIMEOUT 100
-- 
2.43.0