[Devel] [PATCH RHEL7 COMMIT] ploop: Never merge discard requests

[Konstantin Khorenko]

The commit is pushed to "branch-rh7-3.10.0-957.1.3.vz7.93.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-957.1.3.vz7.83.17
------>
commit c47bf5c881565da951c7d3b1cca0da9406457e18
Author: Kirill Tkhai <ktkhai at virtuozzo.com>
Date:   Wed Mar 6 14:22:48 2019 +0300

    ploop: Never merge discard requests
    
    The further architecture of discard for ploop1 format
    looks for me as following.
    
    blkdev_issue_discard() splits big region into requests
    of one block size ((preq->req_size == 1<<plo->cluster_log).
    Then requests each other completes in a separate, so we
    continue existing data ---> index_writeback scheme.
    Another approach, when we try to merge writing of indexes,
    which are related to one index page, does not look for me
    good, since all the existing code was never written in
    an assumption, that a request may iterate on different
    index writing, and this will introduce more corner cases,
    when we already have in ploop.
    
    For raw format this won't introduce any changes in case
    of fstrim, since fstrim sends a request of maximum free
    space it sees at a moment. This will touch only online
    discard option for ext4, when freed block is not big enough,
    but it still will be discardable via fstrim.
    
    Signed-off-by: Kirill Tkhai <ktkhai at virtuozzo.com>
    
    =====================
    Patchset description:
    
    ploop: Add online discard support for dio engine
    
    The first part of patchset is preparations to make code
    a bit readable.
    
    The second part adds online discard support for dio engine.
    DIO engine tracks entents, so discard code will use that
    for its needs.
    
    https://pmc.acronis.com/browse/VSTOR-19972
    
    Kirill Tkhai (12):
          ploop: introduce dio_may_fallocate() helper
          ploop: Export whole_block()
          ploop: Add cluster_size_in_bytes() helper
          ploop: Add cluster_size_in_sec() helper
          ploop: Add local variable into dio_submit()
          ploop: Add cluster_log local variable
          ploop: Add trim_extent_mappings_tail() helper
          ploop: Introduce local variable in ploop_start()
          ploop: Never merge discard requests
          ploop: Set up discard limits
          ploop: Introduce ploop_can_issue_discard() helper
          ploop: Online discard support for dio engine
---
 drivers/block/ploop/dev.c   | 8 +++-----
 include/linux/ploop/ploop.h | 2 +-
 2 files changed, 4 insertions(+), 6 deletions(-)

diff --git a/drivers/block/ploop/dev.c b/drivers/block/ploop/dev.c
index 060aa8bcdfde..9ac436201b1b 100644
--- a/drivers/block/ploop/dev.c
+++ b/drivers/block/ploop/dev.c
@@ -288,9 +288,7 @@ static void preq_set_sync_bit(struct ploop_request * preq)
 
 static struct rb_root *req_entry_tree(struct ploop_device *plo, unsigned rw)
 {
-	if (rw & REQ_DISCARD)
-		return plo->entry_tree + 2;
-	else if (rw & REQ_WRITE)
+	if (rw & REQ_WRITE)
 		return plo->entry_tree + 1;
 	return plo->entry_tree + 0;
 }
@@ -597,7 +595,7 @@ ploop_bio_queue(struct ploop_device * plo, struct bio * bio,
 		plo->bio_qlen--;
 	ploop_entry_add(plo, preq);
 
-	if (bio->bi_size && !(preq->state & (1 << PLOOP_REQ_DISCARD)))
+	if (bio->bi_size && !(bio->bi_rw & REQ_DISCARD))
 		insert_entry_tree(plo, preq, drop_list);
 
 	trace_bio_queue(preq);
@@ -5325,7 +5323,7 @@ static struct ploop_device *__ploop_dev_alloc(int index)
 	plo->freeze_timer.function = freeze_timeout;
 	plo->freeze_timer.data = (unsigned long)plo;
 	INIT_LIST_HEAD(&plo->entry_queue);
-	plo->entry_tree[0] = plo->entry_tree[1] = plo->entry_tree[2] = RB_ROOT;
+	plo->entry_tree[0] = plo->entry_tree[1] = RB_ROOT;
 	plo->lockout_tree = RB_ROOT;
 	plo->lockout_pb_tree = RB_ROOT;
 	INIT_LIST_HEAD(&plo->ready_queue);
diff --git a/include/linux/ploop/ploop.h b/include/linux/ploop/ploop.h
index 58154219d7cb..71a55573bdf6 100644
--- a/include/linux/ploop/ploop.h
+++ b/include/linux/ploop/ploop.h
@@ -382,7 +382,7 @@ struct ploop_device
 	int			bio_qlen;
 	int			bio_total;
 
-	struct rb_root		entry_tree[3];
+	struct rb_root		entry_tree[2];
 
 	struct list_head	ready_queue;