drbd: get rid of bio_split, allow bios of "arbitrary" size

Where "arbitrary" size is currently 1 MiB, which is the BIO_MAX_SIZE
for architectures with 4k PAGE_CACHE_SIZE (most).

Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>

2 files changed, 28 insertions, 84 deletions

diff --git a/drivers/block/drbd/drbd_int.h b/drivers/block/drbd/drbd_int.h
index 8f43a366b82c..2dbffb3b5485 100644
--- a/drivers/block/drbd/drbd_int.h
+++ b/drivers/block/drbd/drbd_int.h
@@ -1326,8 +1326,16 @@ struct bm_extent {
 #endif
 #endif
 
-#define HT_SHIFT 8
-#define DRBD_MAX_BIO_SIZE (1U<<(9+HT_SHIFT))
+/* BIO_MAX_SIZE is 256 * PAGE_CACHE_SIZE,
+ * so for typical PAGE_CACHE_SIZE of 4k, that is (1<<20) Byte.
+ * Since we may live in a mixed-platform cluster,
+ * we limit us to a platform agnostic constant here for now.
+ * A followup commit may allow even bigger BIO sizes,
+ * once we thought that through. */
+#define DRBD_MAX_BIO_SIZE (1 << 20)
+#if DRBD_MAX_BIO_SIZE > BIO_MAX_SIZE
+#error Architecture not supported: DRBD_MAX_BIO_SIZE > BIO_MAX_SIZE
+#endif
 #define DRBD_MAX_BIO_SIZE_SAFE (1 << 12)       /* Works always = 4k */
 
 #define DRBD_MAX_SIZE_H80_PACKET (1 << 15) /* The old header only allows packets up to 32Kib data */
@@ -2231,20 +2239,20 @@ static inline bool may_inc_ap_bio(struct drbd_conf *mdev)
         return true;
 }
 
-static inline bool inc_ap_bio_cond(struct drbd_conf *mdev, int count)
+static inline bool inc_ap_bio_cond(struct drbd_conf *mdev)
 {
         bool rv = false;
 
         spin_lock_irq(&mdev->tconn->req_lock);
         rv = may_inc_ap_bio(mdev);
         if (rv)
-                atomic_add(count, &mdev->ap_bio_cnt);
+                atomic_inc(&mdev->ap_bio_cnt);
         spin_unlock_irq(&mdev->tconn->req_lock);
 
         return rv;
 }
 
-static inline void inc_ap_bio(struct drbd_conf *mdev, int count)
+static inline void inc_ap_bio(struct drbd_conf *mdev)
 {
         /* we wait here
          *    as long as the device is suspended
@@ -2254,7 +2262,7 @@ static inline void inc_ap_bio(struct drbd_conf *mdev, int count)
          * to avoid races with the reconnect code,
          * we need to atomic_inc within the spinlock. */
 
-        wait_event(mdev->misc_wait, inc_ap_bio_cond(mdev, count));
+        wait_event(mdev->misc_wait, inc_ap_bio_cond(mdev));
 }
 
 static inline void dec_ap_bio(struct drbd_conf *mdev)
diff --git a/drivers/block/drbd/drbd_req.c b/drivers/block/drbd/drbd_req.c
index 4406d829800f..6e0e3bb33167 100644
--- a/drivers/block/drbd/drbd_req.c
+++ b/drivers/block/drbd/drbd_req.c
@@ -998,7 +998,6 @@ fail_and_free_req:
 
 int drbd_make_request(struct request_queue *q, struct bio *bio)
 {
-        unsigned int s_enr, e_enr;
         struct drbd_conf *mdev = (struct drbd_conf *) q->queuedata;
         unsigned long start_time;
 
@@ -1010,93 +1009,30 @@ int drbd_make_request(struct request_queue *q, struct bio *bio)
         D_ASSERT(bio->bi_size > 0);
         D_ASSERT(IS_ALIGNED(bio->bi_size, 512));
 
-        /* to make some things easier, force alignment of requests within the
-         * granularity of our hash tables */
-        s_enr = bio->bi_sector >> HT_SHIFT;
-        e_enr = (bio->bi_sector+(bio->bi_size>>9)-1) >> HT_SHIFT;
-
-        if (likely(s_enr == e_enr)) {
-                inc_ap_bio(mdev, 1);
-                return __drbd_make_request(mdev, bio, start_time);
-        }
-
-        /* can this bio be split generically?
-         * Maybe add our own split-arbitrary-bios function. */
-        if (bio->bi_vcnt != 1 || bio->bi_idx != 0 || bio->bi_size > DRBD_MAX_BIO_SIZE) {
-                /* rather error out here than BUG in bio_split */
-                dev_err(DEV, "bio would need to, but cannot, be split: "
-                    "(vcnt=%u,idx=%u,size=%u,sector=%llu)\n",
-                    bio->bi_vcnt, bio->bi_idx, bio->bi_size,
-                    (unsigned long long)bio->bi_sector);
-                bio_endio(bio, -EINVAL);
-        } else {
-                /* This bio crosses some boundary, so we have to split it. */
-                struct bio_pair *bp;
-                /* works for the "do not cross hash slot boundaries" case
-                 * e.g. sector 262269, size 4096
-                 * s_enr = 262269 >> 6 = 4097
-                 * e_enr = (262269+8-1) >> 6 = 4098
-                 * HT_SHIFT = 6
-                 * sps = 64, mask = 63
-                 * first_sectors = 64 - (262269 & 63) = 3
-                 */
-                const sector_t sect = bio->bi_sector;
-                const int sps = 1 << HT_SHIFT; /* sectors per slot */
-                const int mask = sps - 1;
-                const sector_t first_sectors = sps - (sect & mask);
-                bp = bio_split(bio, first_sectors);
-
-                /* we need to get a "reference count" (ap_bio_cnt)
-                 * to avoid races with the disconnect/reconnect/suspend code.
-                 * In case we need to split the bio here, we need to get three references
-                 * atomically, otherwise we might deadlock when trying to submit the
-                 * second one! */
-                inc_ap_bio(mdev, 3);
-
-                D_ASSERT(e_enr == s_enr + 1);
-
-                while (__drbd_make_request(mdev, &bp->bio1, start_time))
-                        inc_ap_bio(mdev, 1);
-
-                while (__drbd_make_request(mdev, &bp->bio2, start_time))
-                        inc_ap_bio(mdev, 1);
-
-                dec_ap_bio(mdev);
-
-                bio_pair_release(bp);
-        }
-        return 0;
+        inc_ap_bio(mdev);
+        return __drbd_make_request(mdev, bio, start_time);
 }
 
-/* This is called by bio_add_page().  With this function we reduce
- * the number of BIOs that span over multiple DRBD_MAX_BIO_SIZEs
- * units (was AL_EXTENTs).
+/* This is called by bio_add_page().
+ *
+ * q->max_hw_sectors and other global limits are already enforced there.
  *
- * we do the calculation within the lower 32bit of the byte offsets,
- * since we don't care for actual offset, but only check whether it
- * would cross "activity log extent" boundaries.
+ * We need to call down to our lower level device,
+ * in case it has special restrictions.
+ *
+ * We also may need to enforce configured max-bio-bvecs limits.
  *
  * As long as the BIO is empty we have to allow at least one bvec,
- * regardless of size and offset.  so the resulting bio may still
- * cross extent boundaries.  those are dealt with (bio_split) in
- * drbd_make_request.
+ * regardless of size and offset, so no need to ask lower levels.
  */
 int drbd_merge_bvec(struct request_queue *q, struct bvec_merge_data *bvm, struct bio_vec *bvec)
 {
         struct drbd_conf *mdev = (struct drbd_conf *) q->queuedata;
-        unsigned int bio_offset =
-                (unsigned int)bvm->bi_sector << 9; /* 32 bit */
         unsigned int bio_size = bvm->bi_size;
-        int limit, backing_limit;
-
-        limit = DRBD_MAX_BIO_SIZE
-              - ((bio_offset & (DRBD_MAX_BIO_SIZE-1)) + bio_size);
-        if (limit < 0)
-                limit = 0;
-        if (bio_size == 0) {
-                if (limit <= bvec->bv_len)
-                        limit = bvec->bv_len;
-        } else if (limit && get_ldev(mdev)) {
+        int limit = DRBD_MAX_BIO_SIZE;
+        int backing_limit;
+
+        if (bio_size && get_ldev(mdev)) {
                 struct request_queue * const b =
                         mdev->ldev->backing_bdev->bd_disk->queue;
                 if (b->merge_bvec_fn) {