linux-kernel - [PATCH] xfs: remove redundant batch variables for serialization

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Message-Id: <20230907123017.1049345-1-alexjlzheng@tencent.com>
Date:   Thu,  7 Sep 2023 20:30:18 +0800
From:   alexjlzheng@...il.com
To:     chandan.babu@...cle.com
Cc:     djwong@...nel.org, linux-xfs@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Jinliang Zheng <alexjlzheng@...cent.com>
Subject: [PATCH] xfs: remove redundant batch variables for serialization

From: Jinliang Zheng <alexjlzheng@...cent.com>

Historically, when generic percpu counters were introduced in xfs for
free block counters by commit 0d485ada404b ("xfs: use generic percpu
counters for free block counter"), the counters use a custom batch size.
In xfs_mod_freecounter(), originally named xfs_mod_fdblocks(), this
patch attempts to serialize the program using a smaller batch size as a
parameter to the addition function as the counter approaches 0.

Commit 8c1903d3081a ("xfs: inode and free block counters need to use
__percpu_counter_compare") pointed out the error in commit 0d485ada404b
("xfs: use generic percpu counters for free block counter") mentioned
above and said that "Because the counters use a custom batch size, the
comparison functions need to be aware of that batch size otherwise the
comparison does not work correctly".

After commit 8c1903d3081a ("xfs: inode and free block counters need to
use __percpu_counter_compare"), the existence of the batch variable is
no longer necessary, so it was removed to simplify the code.

Signed-off-by: Jinliang Zheng <alexjlzheng@...cent.com>
---
 fs/xfs/xfs_mount.c | 17 +----------------
 1 file changed, 1 insertion(+), 16 deletions(-)

diff --git a/fs/xfs/xfs_mount.c b/fs/xfs/xfs_mount.c
index 0a0fd19573d8..72dab39376b7 100644
--- a/fs/xfs/xfs_mount.c
+++ b/fs/xfs/xfs_mount.c
@@ -1144,7 +1144,6 @@ xfs_mod_freecounter(
 	int64_t			lcounter;
 	long long		res_used;
 	uint64_t		set_aside = 0;
-	s32			batch;
 	bool			has_resv_pool;

 	ASSERT(counter == &mp->m_fdblocks || counter == &mp->m_frextents);
@@ -1177,20 +1176,6 @@ xfs_mod_freecounter(
 		return 0;
 	}

-	/*
-	 * Taking blocks away, need to be more accurate the closer we
-	 * are to zero.
-	 *
-	 * If the counter has a value of less than 2 * max batch size,
-	 * then make everything serialise as we are real close to
-	 * ENOSPC.
-	 */
-	if (__percpu_counter_compare(counter, 2 * XFS_FDBLOCKS_BATCH,
-				     XFS_FDBLOCKS_BATCH) < 0)
-		batch = 1;
-	else
-		batch = XFS_FDBLOCKS_BATCH;
-
 	/*
 	 * Set aside allocbt blocks because these blocks are tracked as free
 	 * space but not available for allocation. Technically this means that a
@@ -1204,7 +1189,7 @@ xfs_mod_freecounter(
 	 */
 	if (has_resv_pool)
 		set_aside = xfs_fdblocks_unavailable(mp);
-	percpu_counter_add_batch(counter, delta, batch);
+	percpu_counter_add_batch(counter, delta, XFS_FDBLOCKS_BATCH);
 	if (__percpu_counter_compare(counter, set_aside,
 				     XFS_FDBLOCKS_BATCH) >= 0) {
 		/* we had space! */
-- 
2.31.1