[Devel] [PATCH RHEL7 COMMIT] cbt: make __blk_cbt_set() smarter

[Konstantin Khorenko]

The commit is pushed to "branch-rh7-3.10.0-327.10.1.vz7.12.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-327.10.1.vz7.12.7
------>
commit 2e588a3537ee6a1eec40c07d7797c521beacae9e
Author: Maxim Patlasov <mpatlasov at virtuozzo.com>
Date:   Tue Apr 12 14:24:15 2016 +0400

    cbt: make __blk_cbt_set() smarter
    
    The patch adds two new args to __blk_cbt_set: pages_missed and idx_first.
    Both are pointers. No logic changed, so far as everybody passes NULL/NULL.
    The next patch will pass non-trivial values.
    
    The idea is to mark slots in cbt->map[idx] that need allocation with
    special flag, save their number in *pages_missed and the first index of
    such a slot in *idx_first. This will be used by next patch.
    
    Signed-off-by: Maxim Patlasov <mpatlasov at virtuozzo.com>
    Acked-by: Dmitry Monakhov <dmonakhov at virtuozzo.com>
---
 block/blk-cbt.c | 26 ++++++++++++++++++--------
 1 file changed, 18 insertions(+), 8 deletions(-)

diff --git a/block/blk-cbt.c b/block/blk-cbt.c
index ee225a4..f83eb96 100644
--- a/block/blk-cbt.c
+++ b/block/blk-cbt.c
@@ -136,7 +136,9 @@ static int cbt_page_alloc(struct cbt_info  **cbt_pp, unsigned long idx,
 }
 
 static int __blk_cbt_set(struct cbt_info  *cbt, blkcnt_t block,
-			  blkcnt_t count, bool in_rcu, bool set)
+			 blkcnt_t count, bool in_rcu, bool set,
+			 unsigned long *pages_missed,
+			 unsigned long *idx_first)
 {
 	struct page *page;
 
@@ -164,7 +166,15 @@ static int __blk_cbt_set(struct cbt_info  *cbt, blkcnt_t block,
 			count -= len;
 			block += len;
 			continue;
-		} else {
+		} else if (pages_missed) {
+			(*pages_missed)++;
+			if (!*idx_first)
+				*idx_first = idx;
+			cbt->map[idx] = CBT_PAGE_MISSED;
+			count -= len;
+			block += len;
+			continue;
+		}  else {
 			if (!set) {
 				/* Nothing to do */
 				count -= len;
@@ -181,7 +191,7 @@ static int __blk_cbt_set(struct cbt_info  *cbt, blkcnt_t block,
 		else if (ret)
 			return ret;
 	}
-	return 0;
+	return (pages_missed && *pages_missed) ? -EAGAIN : 0;
 }
 
 static void blk_cbt_add(struct request_queue *q, blkcnt_t start, blkcnt_t len)
@@ -203,7 +213,7 @@ static void blk_cbt_add(struct request_queue *q, blkcnt_t start, blkcnt_t len)
 	start >>= cbt->block_bits;
 	len = end - start;
 	if (unlikely(test_bit(CBT_NOCACHE, &cbt->flags))) {
-		__blk_cbt_set(cbt, start, len, 1, 1);
+		__blk_cbt_set(cbt, start, len, 1, 1, NULL, NULL);
 		goto out_rcu;
 	}
 	ex = this_cpu_ptr(cbt->cache);
@@ -216,7 +226,7 @@ static void blk_cbt_add(struct request_queue *q, blkcnt_t start, blkcnt_t len)
 	ex->len = len;
 
 	if (likely(old.len))
-		__blk_cbt_set(cbt, old.start, old.len, 1, 1);
+		__blk_cbt_set(cbt, old.start, old.len, 1, 1, NULL, NULL);
 out_rcu:
 	rcu_read_unlock();
 }
@@ -401,7 +411,7 @@ static inline void __cbt_flush_cpu_cache(void *ptr)
 	struct cbt_extent *ex = this_cpu_ptr(cbt->cache);
 
 	if (ex->len) {
-		__blk_cbt_set(cbt, ex->start, ex->len, 0, 1);
+		__blk_cbt_set(cbt, ex->start, ex->len, 0, 1, NULL, NULL);
 		ex->start += ex->len;
 		ex->len = 0;
 	}
@@ -522,7 +532,7 @@ static int cbt_ioc_get(struct block_device *bdev, struct blk_user_cbt_info __use
 			break;
 		}
 		if (ci.ci_flags & CI_FLAG_ONCE)
-			__blk_cbt_set(cbt, ex.start, ex.len, 0, 0);
+			__blk_cbt_set(cbt, ex.start, ex.len, 0, 0, NULL, NULL);
 		cur_u_ex++;
 		ci.ci_mapped_extents++;
 		block = ex.start + ex.len;
@@ -592,7 +602,7 @@ static int cbt_ioc_set(struct block_device *bdev, struct blk_user_cbt_info __use
 			ret = -EINVAL;
 			break;
 		}
-		ret = __blk_cbt_set(cbt, ex.start, ex.len, 0, set);
+		ret = __blk_cbt_set(cbt, ex.start, ex.len, 0, set, NULL, NULL);
 		if (ret)
 			break;
 		cur_u_ex++;