linux-ext4 - [RFC 5/8] ext4: Abstract out overlap fix/check logic in ext4_mb_normalize

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Message-Id: <234312071f65ed3a66e9f3472082a745f575e50e.1661632343.git.ojaswin@linux.ibm.com>
Date:   Sun, 28 Aug 2022 12:16:18 +0530
From:   Ojaswin Mujoo <ojaswin@...ux.ibm.com>
To:     linux-ext4@...r.kernel.org
Cc:     "Theodore Ts'o" <tytso@....edu>,
        Ritesh Harjani <riteshh@...ux.ibm.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        Ritesh Harjani <ritesh.list@...il.com>
Subject: [RFC 5/8] ext4: Abstract out overlap fix/check logic in ext4_mb_normalize_request()

Abstract out the logic of fixing PA overlaps in ext4_mb_normalize_request to
improve readability of code. This also makes it easier to make changes
to the overlap logic in future.

There are no functional changes in this patch

Signed-off-by: Ojaswin Mujoo <ojaswin@...ux.ibm.com>
Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@...il.com>
---
 fs/ext4/mballoc.c | 110 +++++++++++++++++++++++++++++-----------------
 1 file changed, 69 insertions(+), 41 deletions(-)

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 8f5aaff892d4..49bc4b8fd849 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -4043,6 +4043,74 @@ ext4_mb_pa_assert_overlap(struct ext4_allocation_context *ac,
 	rcu_read_unlock();
 }
 
+/*
+ * Given an allocation context "ac" and a range "start", "end", check
+ * and adjust boundaries if the range overlaps with any of the existing
+ * preallocatoins stored in the corresponding inode of the allocation context.
+ *
+ *Parameters:
+ *	ac			allocation context
+ *	start			start of the new range
+ *	end			end of the new range
+ */
+static inline void
+ext4_mb_pa_adjust_overlap(struct ext4_allocation_context *ac,
+			 ext4_lblk_t *start, ext4_lblk_t *end)
+{
+	struct ext4_inode_info *ei = EXT4_I(ac->ac_inode);
+	struct ext4_sb_info *sbi = EXT4_SB(ac->ac_sb);
+	struct ext4_prealloc_space *tmp_pa;
+	ext4_lblk_t new_start, new_end;
+	ext4_lblk_t tmp_pa_start, tmp_pa_end;
+
+	new_start = *start;
+	new_end = *end;
+
+	/* check we don't cross already preallocated blocks */
+	rcu_read_lock();
+	list_for_each_entry_rcu(tmp_pa, &ei->i_prealloc_list, pa_inode_list) {
+		if (tmp_pa->pa_deleted)
+			continue;
+		spin_lock(&tmp_pa->pa_lock);
+		if (tmp_pa->pa_deleted) {
+			spin_unlock(&tmp_pa->pa_lock);
+			continue;
+		}
+
+		tmp_pa_start = tmp_pa->pa_lstart;
+		tmp_pa_end = tmp_pa->pa_lstart + EXT4_C2B(sbi, tmp_pa->pa_len);
+
+		/* PA must not overlap original request */
+		BUG_ON(!(ac->ac_o_ex.fe_logical >= tmp_pa_end ||
+			ac->ac_o_ex.fe_logical < tmp_pa_start));
+
+		/* skip PAs this normalized request doesn't overlap with */
+		if (tmp_pa_start >= new_end || tmp_pa_end <= new_start) {
+			spin_unlock(&tmp_pa->pa_lock);
+			continue;
+		}
+		BUG_ON(tmp_pa_start <= new_start && tmp_pa_end >= new_end);
+
+		/* adjust start or end to be adjacent to this pa */
+		if (tmp_pa_end <= ac->ac_o_ex.fe_logical) {
+			BUG_ON(tmp_pa_end < new_start);
+			new_start = tmp_pa_end;
+		} else if (tmp_pa_start > ac->ac_o_ex.fe_logical) {
+			BUG_ON(tmp_pa_start > new_end);
+			new_end = tmp_pa_start;
+		}
+		spin_unlock(&tmp_pa->pa_lock);
+	}
+	rcu_read_unlock();
+
+	/* XXX: extra loop to check we really don't overlap preallocations */
+	ext4_mb_pa_assert_overlap(ac, new_start, new_end);
+
+	*start = new_start;
+	*end = new_end;
+	return;
+}
+
 /*
  * Normalization means making request better in terms of
  * size and alignment
@@ -4057,9 +4125,6 @@ ext4_mb_normalize_request(struct ext4_allocation_context *ac,
 	loff_t size, start_off;
 	loff_t orig_size __maybe_unused;
 	ext4_lblk_t start;
-	struct ext4_inode_info *ei = EXT4_I(ac->ac_inode);
-	struct ext4_prealloc_space *tmp_pa;
-	ext4_lblk_t tmp_pa_start, tmp_pa_end;
 
 	/* do normalize only data requests, metadata requests
 	   do not need preallocation */
@@ -4160,47 +4225,10 @@ ext4_mb_normalize_request(struct ext4_allocation_context *ac,
 
 	end = start + size;
 
-	/* check we don't cross already preallocated blocks */
-	rcu_read_lock();
-	list_for_each_entry_rcu(tmp_pa, &ei->i_prealloc_list, pa_inode_list) {
-		if (tmp_pa->pa_deleted)
-			continue;
-		spin_lock(&tmp_pa->pa_lock);
-		if (tmp_pa->pa_deleted) {
-			spin_unlock(&tmp_pa->pa_lock);
-			continue;
-		}
-
-		tmp_pa_start = tmp_pa->pa_lstart;
-		tmp_pa_end = tmp_pa->pa_lstart + EXT4_C2B(sbi, tmp_pa->pa_len);
-
-		/* PA must not overlap original request */
-		BUG_ON(!(ac->ac_o_ex.fe_logical >= tmp_pa_end ||
-			ac->ac_o_ex.fe_logical < tmp_pa_start));
-
-		/* skip PAs this normalized request doesn't overlap with */
-		if (tmp_pa_start >= end || tmp_pa_end <= start) {
-			spin_unlock(&tmp_pa->pa_lock);
-			continue;
-		}
-		BUG_ON(tmp_pa_start <= start && tmp_pa_end >= end);
+	ext4_mb_pa_adjust_overlap(ac, &start, &end);
 
-		/* adjust start or end to be adjacent to this pa */
-		if (tmp_pa_end <= ac->ac_o_ex.fe_logical) {
-			BUG_ON(tmp_pa_end < start);
-			start = tmp_pa_end;
-		} else if (tmp_pa_start > ac->ac_o_ex.fe_logical) {
-			BUG_ON(tmp_pa_start > end);
-			end = tmp_pa_start;
-		}
-		spin_unlock(&tmp_pa->pa_lock);
-	}
-	rcu_read_unlock();
 	size = end - start;
 
-	/* XXX: extra loop to check we really don't overlap preallocations */
-	ext4_mb_pa_assert_overlap(ac, start, end);
-
 	/*
 	 * In this function "start" and "size" are normalized for better
 	 * alignment and length such that we could preallocate more blocks.
-- 
2.31.1