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

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Message-ID: <0be88aea-9438-2c74-762e-b8aaa549fd40@huawei.com>
Date: Wed, 14 Aug 2024 09:33:05 +0800
From: Zhihao Cheng <chengzhihao1@...wei.com>
To: Mateusz Guzik <mjguzik@...il.com>, <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>
Subject: Re: [PATCH] vfs: drop one lock trip in evict()

在 2024/8/13 22:36, Mateusz Guzik 写道:
> 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>
> ---

Reviewed-by: Zhihao Cheng <chengzhihao1@...wei.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);
>