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Subject[PATCH 15/16] drbd: get rid of bio_split, allow bios of "arbitrary" size
Date
From: Lars Ellenberg <lars.ellenberg@linbit.com>

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>
---
drivers/block/drbd/drbd_int.h | 20 ++++++---
drivers/block/drbd/drbd_req.c | 92 ++++++----------------------------------
2 files changed, 28 insertions(+), 84 deletions(-)
diff --git a/drivers/block/drbd/drbd_int.h b/drivers/block/drbd/drbd_int.h
index 218e2c3..54eb96a 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 4406d82..6e0e3bb 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) {
--
1.7.4.1


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