linux-kernel - [PATCH] vfs: drop one lock trip in evict()

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Message-ID: <20240813143626.1573445-1-mjguzik@gmail.com>
Date: Tue, 13 Aug 2024 16:36:26 +0200
From: Mateusz Guzik <mjguzik@...il.com>
To: brauner@...nel.org
Cc: viro@...iv.linux.org.uk,
	jack@...e.cz,
	jlayton@...nel.org,
	linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org,
	Mateusz Guzik <mjguzik@...il.com>
Subject: [PATCH] vfs: drop one lock trip in evict()

Most commonly neither I_LRU_ISOLATING nor I_SYNC are set, but the stock
kernel takes a back-to-back relock trip to check for them.

It probably can be avoided altogether, but for now massage things back
to just one lock acquire.

Signed-off-by: Mateusz Guzik <mjguzik@...il.com>
---

there are smp_mb's in the area I'm going to look at removing at some
point(tm), in the meantime I think this is an easy cleanup

has a side effect of whacking a inode_wait_for_writeback which was only
there to deal with not holding the lock

 fs/fs-writeback.c | 17 +++--------------
 fs/inode.c        |  5 +++--
 2 files changed, 6 insertions(+), 16 deletions(-)

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 4451ecff37c4..1a5006329f6f 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -1510,13 +1510,12 @@ static int write_inode(struct inode *inode, struct writeback_control *wbc)
  * Wait for writeback on an inode to complete. Called with i_lock held.
  * Caller must make sure inode cannot go away when we drop i_lock.
  */
-static void __inode_wait_for_writeback(struct inode *inode)
-	__releases(inode->i_lock)
-	__acquires(inode->i_lock)
+void inode_wait_for_writeback(struct inode *inode)
 {
 	DEFINE_WAIT_BIT(wq, &inode->i_state, __I_SYNC);
 	wait_queue_head_t *wqh;
 
+	lockdep_assert_held(&inode->i_lock);
 	wqh = bit_waitqueue(&inode->i_state, __I_SYNC);
 	while (inode->i_state & I_SYNC) {
 		spin_unlock(&inode->i_lock);
@@ -1526,16 +1525,6 @@ static void __inode_wait_for_writeback(struct inode *inode)
 	}
 }
 
-/*
- * Wait for writeback on an inode to complete. Caller must have inode pinned.
- */
-void inode_wait_for_writeback(struct inode *inode)
-{
-	spin_lock(&inode->i_lock);
-	__inode_wait_for_writeback(inode);
-	spin_unlock(&inode->i_lock);
-}
-
 /*
  * Sleep until I_SYNC is cleared. This function must be called with i_lock
  * held and drops it. It is aimed for callers not holding any inode reference
@@ -1757,7 +1746,7 @@ static int writeback_single_inode(struct inode *inode,
 		 */
 		if (wbc->sync_mode != WB_SYNC_ALL)
 			goto out;
-		__inode_wait_for_writeback(inode);
+		inode_wait_for_writeback(inode);
 	}
 	WARN_ON(inode->i_state & I_SYNC);
 	/*
diff --git a/fs/inode.c b/fs/inode.c
index 73183a499b1c..d48d29d39cd2 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -582,7 +582,7 @@ static void inode_unpin_lru_isolating(struct inode *inode)
 
 static void inode_wait_for_lru_isolating(struct inode *inode)
 {
-	spin_lock(&inode->i_lock);
+	lockdep_assert_held(&inode->i_lock);
 	if (inode->i_state & I_LRU_ISOLATING) {
 		DEFINE_WAIT_BIT(wq, &inode->i_state, __I_LRU_ISOLATING);
 		wait_queue_head_t *wqh;
@@ -593,7 +593,6 @@ static void inode_wait_for_lru_isolating(struct inode *inode)
 		spin_lock(&inode->i_lock);
 		WARN_ON(inode->i_state & I_LRU_ISOLATING);
 	}
-	spin_unlock(&inode->i_lock);
 }
 
 /**
@@ -765,6 +764,7 @@ static void evict(struct inode *inode)
 
 	inode_sb_list_del(inode);
 
+	spin_lock(&inode->i_lock);
 	inode_wait_for_lru_isolating(inode);
 
 	/*
@@ -774,6 +774,7 @@ static void evict(struct inode *inode)
 	 * the inode.  We just have to wait for running writeback to finish.
 	 */
 	inode_wait_for_writeback(inode);
+	spin_unlock(&inode->i_lock);
 
 	if (op->evict_inode) {
 		op->evict_inode(inode);
-- 
2.43.0