[PATCH v2 1/2] block: Add bvec_folio()

[Matthew Wilcox (Oracle)]

This is a simple helper which replaces page_folio(bvec->bv_page).
Minor improvement in readability, but the real motivation is to reduce
the number of references to bvec->bv_page so that it can be changed
with less work.

Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Cc: Leon Romanovsky <leon@xxxxxxxxxx>
---
 block/bio.c          |  6 +++---
 include/linux/bio.h  |  2 +-
 include/linux/bvec.h | 15 +++++++++++++++
 io_uring/rsrc.c      |  2 +-
 mm/page_io.c         |  4 ++--
 5 files changed, 22 insertions(+), 7 deletions(-)

diff --git a/block/bio.c b/block/bio.c
index 5f10900b3f42..85aab3140909 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -1300,7 +1300,7 @@ static void bio_free_folios(struct bio *bio)
 	int i;
 
 	bio_for_each_bvec_all(bv, bio, i) {
-		struct folio *folio = page_folio(bv->bv_page);
+		struct folio *folio = bvec_folio(bv);
 
 		if (!is_zero_folio(folio))
 			folio_put(folio);
@@ -1409,7 +1409,7 @@ int bio_iov_iter_bounce(struct bio *bio, struct iov_iter *iter, size_t maxlen,
 
 static void bvec_unpin(struct bio_vec *bv, bool mark_dirty)
 {
-	struct folio *folio = page_folio(bv->bv_page);
+	struct folio *folio = bvec_folio(bv);
 	size_t nr_pages = (bv->bv_offset + bv->bv_len - 1) / PAGE_SIZE -
 			bv->bv_offset / PAGE_SIZE + 1;
 
@@ -1443,7 +1443,7 @@ static void bio_iov_iter_unbounce_read(struct bio *bio, bool is_error,
 			bvec_unpin(&bio->bi_io_vec[1 + i], mark_dirty);
 	}
 
-	folio_put(page_folio(bio->bi_io_vec[0].bv_page));
+	folio_put(bvec_folio(&bio->bi_io_vec[0]));
 }
 
 /**
diff --git a/include/linux/bio.h b/include/linux/bio.h
index dc17780d6c1e..6613ab4519bd 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -283,7 +283,7 @@ static inline void bio_first_folio(struct folio_iter *fi, struct bio *bio,
 		return;
 	}
 
-	fi->folio = page_folio(bvec->bv_page);
+	fi->folio = bvec_folio(bvec);
 	fi->offset = bvec->bv_offset +
 			PAGE_SIZE * folio_page_idx(fi->folio, bvec->bv_page);
 	fi->_seg_count = bvec->bv_len;
diff --git a/include/linux/bvec.h b/include/linux/bvec.h
index d36dd476feda..27ac3fcc6d9e 100644
--- a/include/linux/bvec.h
+++ b/include/linux/bvec.h
@@ -74,6 +74,21 @@ static inline void bvec_set_virt(struct bio_vec *bv, void *vaddr,
 	bvec_set_page(bv, virt_to_page(vaddr), len, offset_in_page(vaddr));
 }
 
+/**
+ * bvec_folio - Return the first folio referenced by this bvec
+ * @bv: bvec to access
+ *
+ * A bvec can contain non-folio memory, so this should only be called by
+ * the creator of the bvec; drivers have no business looking at the owner
+ * of the memory.  It may not even be the right interface for the caller
+ * to use as a bvec can span multiple folios.  You may be better off using
+ * something like bio_for_each_folio_all() which iterates over all folios.
+ */
+static inline struct folio *bvec_folio(const struct bio_vec *bv)
+{
+	return page_folio(bv->bv_page);
+}
+
 struct bvec_iter {
 	/*
 	 * Current device address in 512 byte sectors. Only updated by the bio
diff --git a/io_uring/rsrc.c b/io_uring/rsrc.c
index 650303626be6..5d792f70ec1e 100644
--- a/io_uring/rsrc.c
+++ b/io_uring/rsrc.c
@@ -102,7 +102,7 @@ static void io_release_ubuf(void *priv)
 	unsigned int i;
 
 	for (i = 0; i < imu->nr_bvecs; i++) {
-		struct folio *folio = page_folio(imu->bvec[i].bv_page);
+		struct folio *folio = bvec_folio(&imu->bvec[i]);
 
 		unpin_user_folio(folio, 1);
 	}
diff --git a/mm/page_io.c b/mm/page_io.c
index 70cea9e24d2f..a59b73f8bdd9 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -490,7 +490,7 @@ static void sio_read_complete(struct kiocb *iocb, long ret)
 
 	if (ret == sio->len) {
 		for (p = 0; p < sio->pages; p++) {
-			struct folio *folio = page_folio(sio->bvec[p].bv_page);
+			struct folio *folio = bvec_folio(&sio->bvec[p]);
 
 			count_mthp_stat(folio_order(folio), MTHP_STAT_SWPIN);
 			count_memcg_folio_events(folio, PSWPIN, folio_nr_pages(folio));
@@ -500,7 +500,7 @@ static void sio_read_complete(struct kiocb *iocb, long ret)
 		count_vm_events(PSWPIN, sio->len >> PAGE_SHIFT);
 	} else {
 		for (p = 0; p < sio->pages; p++) {
-			struct folio *folio = page_folio(sio->bvec[p].bv_page);
+			struct folio *folio = bvec_folio(&sio->bvec[p]);
 
 			folio_unlock(folio);
 		}
-- 
2.47.3