[PATCH v2] mm: swap: remove 'synchronous' argument to swap_read_folio()

[Yosry Ahmed]

Commit [1] introduced IO polling support duding swapin to reduce swap read
latency for block devices that can be polled.  However later commit [2]
removed polling support. Commit [3] removed the remnants of polling
support from read_swap_cache_async() and __read_swap_cache_async().
However, it left behind some remnants in swap_read_folio(), the
'synchronous' argument.

swap_read_folio() reads the folio synchronously if synchronous=true or
if SWP_SYNCHRONOUS_IO is set in swap_info_struct. The only caller that
passes synchronous=true is in do_swap_page() in the SWP_SYNCHRONOUS_IO
case.

Hence, the argument is redundant, it is only set to true when the swap
read would have been synchronous anyway. Remove it.

[1] Commit 23955622ff8d ("swap: add block io poll in swapin path")
[2] Commit 9650b453a3d4 ("block: ignore RWF_HIPRI hint for sync dio")
[3] Commit b243dcbf2f13 ("swap: remove remnants of polling from read_swap_cache_async")

Reviewed-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
Signed-off-by: Yosry Ahmed <yosryahmed@xxxxxxxxxx>
---

v1 -> v2:
- Collected Reviewed-by (Thanks Ying!).
- Added some historical context in the commit log (Ying).

---
 mm/memory.c     |  2 +-
 mm/page_io.c    |  6 +++---
 mm/swap.h       |  6 ++----
 mm/swap_state.c | 10 +++++-----
 4 files changed, 11 insertions(+), 13 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index db91304882312..2b3ef08e8bb7d 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -4113,7 +4113,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
 
 				/* To provide entry to swap_read_folio() */
 				folio->swap = entry;
-				swap_read_folio(folio, true, NULL);
+				swap_read_folio(folio, NULL);
 				folio->private = NULL;
 			}
 		} else {
diff --git a/mm/page_io.c b/mm/page_io.c
index 41e8d738c6d28..f1a9cfab6e748 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -493,10 +493,10 @@ static void swap_read_folio_bdev_async(struct folio *folio,
 	submit_bio(bio);
 }
 
-void swap_read_folio(struct folio *folio, bool synchronous,
-		struct swap_iocb **plug)
+void swap_read_folio(struct folio *folio, struct swap_iocb **plug)
 {
 	struct swap_info_struct *sis = swp_swap_info(folio->swap);
+	bool synchronous = sis->flags & SWP_SYNCHRONOUS_IO;
 	bool workingset = folio_test_workingset(folio);
 	unsigned long pflags;
 	bool in_thrashing;
@@ -521,7 +521,7 @@ void swap_read_folio(struct folio *folio, bool synchronous,
 		folio_unlock(folio);
 	} else if (data_race(sis->flags & SWP_FS_OPS)) {
 		swap_read_folio_fs(folio, plug);
-	} else if (synchronous || (sis->flags & SWP_SYNCHRONOUS_IO)) {
+	} else if (synchronous) {
 		swap_read_folio_bdev_sync(folio, sis);
 	} else {
 		swap_read_folio_bdev_async(folio, sis);
diff --git a/mm/swap.h b/mm/swap.h
index 2c0e96272d498..baa1fa946b347 100644
--- a/mm/swap.h
+++ b/mm/swap.h
@@ -11,8 +11,7 @@ struct mempolicy;
 /* linux/mm/page_io.c */
 int sio_pool_init(void);
 struct swap_iocb;
-void swap_read_folio(struct folio *folio, bool do_poll,
-		struct swap_iocb **plug);
+void swap_read_folio(struct folio *folio, struct swap_iocb **plug);
 void __swap_read_unplug(struct swap_iocb *plug);
 static inline void swap_read_unplug(struct swap_iocb *plug)
 {
@@ -83,8 +82,7 @@ static inline unsigned int folio_swap_flags(struct folio *folio)
 }
 #else /* CONFIG_SWAP */
 struct swap_iocb;
-static inline void swap_read_folio(struct folio *folio, bool do_poll,
-		struct swap_iocb **plug)
+static inline void swap_read_folio(struct folio *folio, struct swap_iocb **plug)
 {
 }
 static inline void swap_write_unplug(struct swap_iocb *sio)
diff --git a/mm/swap_state.c b/mm/swap_state.c
index 0803eedeabe3d..994723cef8217 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -567,7 +567,7 @@ struct folio *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
 	mpol_cond_put(mpol);
 
 	if (page_allocated)
-		swap_read_folio(folio, false, plug);
+		swap_read_folio(folio, plug);
 	return folio;
 }
 
@@ -684,7 +684,7 @@ struct folio *swap_cluster_readahead(swp_entry_t entry, gfp_t gfp_mask,
 		if (!folio)
 			continue;
 		if (page_allocated) {
-			swap_read_folio(folio, false, &splug);
+			swap_read_folio(folio, &splug);
 			if (offset != entry_offset) {
 				folio_set_readahead(folio);
 				count_vm_event(SWAP_RA);
@@ -701,7 +701,7 @@ struct folio *swap_cluster_readahead(swp_entry_t entry, gfp_t gfp_mask,
 					&page_allocated, false);
 	if (unlikely(page_allocated)) {
 		zswap_folio_swapin(folio);
-		swap_read_folio(folio, false, NULL);
+		swap_read_folio(folio, NULL);
 	}
 	return folio;
 }
@@ -834,7 +834,7 @@ static struct folio *swap_vma_readahead(swp_entry_t targ_entry, gfp_t gfp_mask,
 		if (!folio)
 			continue;
 		if (page_allocated) {
-			swap_read_folio(folio, false, &splug);
+			swap_read_folio(folio, &splug);
 			if (addr != vmf->address) {
 				folio_set_readahead(folio);
 				count_vm_event(SWAP_RA);
@@ -853,7 +853,7 @@ static struct folio *swap_vma_readahead(swp_entry_t targ_entry, gfp_t gfp_mask,
 					&page_allocated, false);
 	if (unlikely(page_allocated)) {
 		zswap_folio_swapin(folio);
-		swap_read_folio(folio, false, NULL);
+		swap_read_folio(folio, NULL);
 	}
 	return folio;
 }
-- 
2.45.2.505.gda0bf45e8d-goog