zram: simplify bvec iteration in __zram_make_request

bio_for_each_segment synthetize bvecs that never cross page boundaries, so
don't duplicate that work in an inner loop.

Link: https://lkml.kernel.org/r/20230411171459.567614-5-hch@lst.de
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

drivers/block/zram/zram_drv.c

@@ -175,12 +175,6 @@ static inline u32 zram_get_priority(struct zram *zram, u32 index)
 	return prio & ZRAM_COMP_PRIORITY_MASK;
 }
 
-static void update_position(u32 *index, int *offset, struct bio_vec *bvec)
-{
-	*index  += (*offset + bvec->bv_len) / PAGE_SIZE;
-	*offset = (*offset + bvec->bv_len) % PAGE_SIZE;
-}
-
 static inline void update_used_max(struct zram *zram,
 					const unsigned long pages)
 {
@@ -1960,16 +1954,10 @@ static int zram_bvec_rw(struct zram *zram, struct bio_vec *bvec, u32 index,
 
 static void __zram_make_request(struct zram *zram, struct bio *bio)
 {
-	int offset;
-	u32 index;
-	struct bio_vec bvec;
 	struct bvec_iter iter;
+	struct bio_vec bv;
 	unsigned long start_time;
 
-	index = bio->bi_iter.bi_sector >> SECTORS_PER_PAGE_SHIFT;
-	offset = (bio->bi_iter.bi_sector &
-		  (SECTORS_PER_PAGE - 1)) << SECTOR_SHIFT;
-
 	switch (bio_op(bio)) {
 	case REQ_OP_DISCARD:
 	case REQ_OP_WRITE_ZEROES:
@@ -1980,24 +1968,16 @@ static void __zram_make_request(struct zram *zram, struct bio *bio)
 	}
 
 	start_time = bio_start_io_acct(bio);
-	bio_for_each_segment(bvec, bio, iter) {
-		struct bio_vec bv = bvec;
-		unsigned int unwritten = bvec.bv_len;
-
-		do {
-			bv.bv_len = min_t(unsigned int, PAGE_SIZE - offset,
-							unwritten);
-			if (zram_bvec_rw(zram, &bv, index, offset,
-					 bio_op(bio), bio) < 0) {
-				bio->bi_status = BLK_STS_IOERR;
-				break;
-			}
-
-			bv.bv_offset += bv.bv_len;
-			unwritten -= bv.bv_len;
-
-			update_position(&index, &offset, &bv);
-		} while (unwritten);
+	bio_for_each_segment(bv, bio, iter) {
+		u32 index = iter.bi_sector >> SECTORS_PER_PAGE_SHIFT;
+		u32 offset = (iter.bi_sector & (SECTORS_PER_PAGE - 1)) <<
+				SECTOR_SHIFT;
+
+		if (zram_bvec_rw(zram, &bv, index, offset, bio_op(bio),
+				bio) < 0) {
+			bio->bi_status = BLK_STS_IOERR;
+			break;
+		}
 	}
 	bio_end_io_acct(bio, start_time);
 	bio_endio(bio);