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Date:   Wed, 7 Jul 2021 18:59:47 +0200
From:   Jan Kara <jack@...e.cz>
To:     Zhang Yi <yi.zhang@...wei.com>
Cc:     linux-ext4@...r.kernel.org, tytso@....edu,
        adilger.kernel@...ger.ca, jack@...e.cz, yukuai3@...wei.com
Subject: Re: [RFC PATCH 4/4] ext4: drop unnecessary journal handle in
 delalloc write

On Tue 06-07-21 10:42:10, Zhang Yi wrote:
> After we factor out the inline data write procedure from
> ext4_da_write_end(), we don't need to start journal handle for the cases
> of both buffer overwrite and append-write. If we need to update
> i_disksize, mark_inode_dirty() do start handle and update inode buffer.
> So we could just remove all the journal handle codes in the delalloc
> write procedure.
> 
> After this patch, we could get a lot of performance improvement. Below
> is the Unixbench comparison data test on my machine with 'Intel Xeon
> Gold 5120' CPU and nvme SSD backend.
> 
> Test cmd:
> 
>   ./Run -c 56 -i 3 fstime fsbuffer fsdisk
> 
> Before this patch:
> 
>   System Benchmarks Partial Index           BASELINE       RESULT   INDEX
>   File Copy 1024 bufsize 2000 maxblocks       3960.0     422965.0   1068.1
>   File Copy 256 bufsize 500 maxblocks         1655.0     105077.0   634.9
>   File Copy 4096 bufsize 8000 maxblocks       5800.0    1429092.0   2464.0
>                                                                     ======
>   System Benchmarks Index Score (Partial Only)                      1186.6
> 
> After this patch:
> 
>   System Benchmarks Partial Index           BASELINE       RESULT   INDEX
>   File Copy 1024 bufsize 2000 maxblocks       3960.0     732716.0   1850.3
>   File Copy 256 bufsize 500 maxblocks         1655.0     184940.0   1117.5
>   File Copy 4096 bufsize 8000 maxblocks       5800.0    2427152.0   4184.7
>                                                                     ======
>   System Benchmarks Index Score (Partial Only)                      2053.0
> 
> Signed-off-by: Zhang Yi <yi.zhang@...wei.com>

Looks good and nice speedup! Feel free to add:

Reviewed-by: Jan Kara <jack@...e.cz>

								Honza

> ---
>  fs/ext4/inode.c | 60 +++++--------------------------------------------
>  1 file changed, 5 insertions(+), 55 deletions(-)
> 
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 650da0648eba..9c86cada9a54 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -2910,19 +2910,6 @@ static int ext4_nonda_switch(struct super_block *sb)
>  	return 0;
>  }
>  
> -/* We always reserve for an inode update; the superblock could be there too */
> -static int ext4_da_write_credits(struct inode *inode, loff_t pos, unsigned len)
> -{
> -	if (likely(ext4_has_feature_large_file(inode->i_sb)))
> -		return 1;
> -
> -	if (pos + len <= 0x7fffffffULL)
> -		return 1;
> -
> -	/* We might need to update the superblock to set LARGE_FILE */
> -	return 2;
> -}
> -
>  static int ext4_da_write_begin(struct file *file, struct address_space *mapping,
>  			       loff_t pos, unsigned len, unsigned flags,
>  			       struct page **pagep, void **fsdata)
> @@ -2931,7 +2918,6 @@ static int ext4_da_write_begin(struct file *file, struct address_space *mapping,
>  	struct page *page;
>  	pgoff_t index;
>  	struct inode *inode = mapping->host;
> -	handle_t *handle;
>  
>  	if (unlikely(ext4_forced_shutdown(EXT4_SB(inode->i_sb))))
>  		return -EIO;
> @@ -2957,41 +2943,11 @@ static int ext4_da_write_begin(struct file *file, struct address_space *mapping,
>  			return 0;
>  	}
>  
> -	/*
> -	 * grab_cache_page_write_begin() can take a long time if the
> -	 * system is thrashing due to memory pressure, or if the page
> -	 * is being written back.  So grab it first before we start
> -	 * the transaction handle.  This also allows us to allocate
> -	 * the page (if needed) without using GFP_NOFS.
> -	 */
> -retry_grab:
> +retry:
>  	page = grab_cache_page_write_begin(mapping, index, flags);
>  	if (!page)
>  		return -ENOMEM;
> -	unlock_page(page);
> -
> -	/*
> -	 * With delayed allocation, we don't log the i_disksize update
> -	 * if there is delayed block allocation. But we still need
> -	 * to journalling the i_disksize update if writes to the end
> -	 * of file which has an already mapped buffer.
> -	 */
> -retry_journal:
> -	handle = ext4_journal_start(inode, EXT4_HT_WRITE_PAGE,
> -				ext4_da_write_credits(inode, pos, len));
> -	if (IS_ERR(handle)) {
> -		put_page(page);
> -		return PTR_ERR(handle);
> -	}
>  
> -	lock_page(page);
> -	if (page->mapping != mapping) {
> -		/* The page got truncated from under us */
> -		unlock_page(page);
> -		put_page(page);
> -		ext4_journal_stop(handle);
> -		goto retry_grab;
> -	}
>  	/* In case writeback began while the page was unlocked */
>  	wait_for_stable_page(page);
>  
> @@ -3003,20 +2959,18 @@ static int ext4_da_write_begin(struct file *file, struct address_space *mapping,
>  #endif
>  	if (ret < 0) {
>  		unlock_page(page);
> -		ext4_journal_stop(handle);
> +		put_page(page);
>  		/*
>  		 * block_write_begin may have instantiated a few blocks
>  		 * outside i_size.  Trim these off again. Don't need
> -		 * i_size_read because we hold i_mutex.
> +		 * i_size_read because we hold inode lock.
>  		 */
>  		if (pos + len > inode->i_size)
>  			ext4_truncate_failed_write(inode);
>  
>  		if (ret == -ENOSPC &&
>  		    ext4_should_retry_alloc(inode->i_sb, &retries))
> -			goto retry_journal;
> -
> -		put_page(page);
> +			goto retry;
>  		return ret;
>  	}
>  
> @@ -3053,8 +3007,6 @@ static int ext4_da_write_end(struct file *file,
>  			     struct page *page, void *fsdata)
>  {
>  	struct inode *inode = mapping->host;
> -	int ret;
> -	handle_t *handle = ext4_journal_current_handle();
>  	loff_t new_i_size;
>  	unsigned long start, end;
>  	int write_mode = (int)(unsigned long)fsdata;
> @@ -3086,9 +3038,7 @@ static int ext4_da_write_end(struct file *file,
>  	    ext4_da_should_update_i_disksize(page, end))
>  		ext4_update_i_disksize(inode, new_i_size);
>  
> -	copied = generic_write_end(file, mapping, pos, len, copied, page, fsdata);
> -	ret = ext4_journal_stop(handle);
> -	return ret ? ret : copied;
> +	return generic_write_end(file, mapping, pos, len, copied, page, fsdata);
>  }
>  
>  /*
> -- 
> 2.31.1
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR

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