filemap: make the accounting of thrashing more consistent

Once upon a time, we only support accounting thrashing of page cache. 
Then Joonsoo introduced workingset detection for anonymous pages and we
gained the ability to account thrashing of them[1].

So let delayacct account both the thrashing of page cache and anonymous
pages, this could make the codes more consistent and simpler.

[1] commit aae466b ("mm/swap: implement workingset detection for anonymous LRU")

Link: https://lkml.kernel.org/r/20220805033838.1714674-1-yang.yang29@zte.com.cn
Signed-off-by: Yang Yang <yang.yang29@zte.com.cn>
Signed-off-by: CGEL ZTE <cgel.zte@gmail.com>
Acked-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Balbir Singh <bsingharora@gmail.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Yang Yang <yang.yang29@zte.com.cn>
Cc: David Hildenbrand <david@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Documentation/accounting/delay-accounting.rst

@@ -13,7 +13,7 @@ a) waiting for a CPU (while being runnable)
 b) completion of synchronous block I/O initiated by the task
 c) swapping in pages
 d) memory reclaim
-e) thrashing page cache
+e) thrashing
 f) direct compact
 g) write-protect copy
 

mm/filemap.c

@@ -1221,15 +1221,11 @@ static inline int folio_wait_bit_common(struct folio *folio, int bit_nr,
 	struct wait_page_queue wait_page;
 	wait_queue_entry_t *wait = &wait_page.wait;
 	bool thrashing = false;
-	bool delayacct = false;
 	unsigned long pflags;
 
 	if (bit_nr == PG_locked &&
 	    !folio_test_uptodate(folio) && folio_test_workingset(folio)) {
-		if (!folio_test_swapbacked(folio)) {
-			delayacct_thrashing_start();
-			delayacct = true;
-		}
+		delayacct_thrashing_start();
 		psi_memstall_enter(&pflags);
 		thrashing = true;
 	}
@@ -1329,8 +1325,7 @@ static inline int folio_wait_bit_common(struct folio *folio, int bit_nr,
 	finish_wait(q, wait);
 
 	if (thrashing) {
-		if (delayacct)
-			delayacct_thrashing_end();
+		delayacct_thrashing_end();
 		psi_memstall_leave(&pflags);
 	}
 
@@ -1378,17 +1373,13 @@ void migration_entry_wait_on_locked(swp_entry_t entry, pte_t *ptep,
 	struct wait_page_queue wait_page;
 	wait_queue_entry_t *wait = &wait_page.wait;
 	bool thrashing = false;
-	bool delayacct = false;
 	unsigned long pflags;
 	wait_queue_head_t *q;
 	struct folio *folio = page_folio(pfn_swap_entry_to_page(entry));
 
 	q = folio_waitqueue(folio);
 	if (!folio_test_uptodate(folio) && folio_test_workingset(folio)) {
-		if (!folio_test_swapbacked(folio)) {
-			delayacct_thrashing_start();
-			delayacct = true;
-		}
+		delayacct_thrashing_start();
 		psi_memstall_enter(&pflags);
 		thrashing = true;
 	}
@@ -1435,8 +1426,7 @@ void migration_entry_wait_on_locked(swp_entry_t entry, pte_t *ptep,
 	finish_wait(q, wait);
 
 	if (thrashing) {
-		if (delayacct)
-			delayacct_thrashing_end();
+		delayacct_thrashing_end();
 		psi_memstall_leave(&pflags);
 	}
 }