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Subject: Re: [PATCHv5 3/6] ext4: Move ext4 bmap to use iomap infrastructure.
To:     "Darrick J. Wong" <darrick.wong@oracle.com>, jack@suse.cz
Cc:     linux-ext4@vger.kernel.org, tytso@mit.edu,
        adilger.kernel@dilger.ca, linux-fsdevel@vger.kernel.org,
        hch@infradead.org, cmaiolino@redhat.com, david@fromorbit.com
References: <cover.1582880246.git.riteshh@linux.ibm.com>
 <8bbd53bd719d5ccfecafcce93f2bf1d7955a44af.1582880246.git.riteshh@linux.ibm.com>
 <20200228152524.GE8036@magnolia>
From:   Ritesh Harjani <riteshh@linux.ibm.com>
Date:   Mon, 2 Mar 2020 14:28:39 +0530
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On 2/28/20 8:55 PM, Darrick J. Wong wrote:
> On Fri, Feb 28, 2020 at 02:56:56PM +0530, Ritesh Harjani wrote:
>> ext4_iomap_begin is already implemented which provides ext4_map_blocks,
>> so just move the API from generic_block_bmap to iomap_bmap for iomap
>> conversion.
>>
>> Signed-off-by: Ritesh Harjani <riteshh@linux.ibm.com>
>> Reviewed-by: Jan Kara <jack@suse.cz>
>> ---
>>   fs/ext4/inode.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
>> index 6cf3b969dc86..81fccbae0aea 100644
>> --- a/fs/ext4/inode.c
>> +++ b/fs/ext4/inode.c
>> @@ -3214,7 +3214,7 @@ static sector_t ext4_bmap(struct address_space *mapping, sector_t block)
>>   			return 0;
>>   	}
>>   
>> -	return generic_block_bmap(mapping, block, ext4_get_block);
>> +	return iomap_bmap(mapping, block, &ext4_iomap_ops);
> 
> /me notes that iomap_bmap will filemap_write_and_wait for you, so one
> could optimize ext4_bmap to avoid the double-flush by moving the
> filemap_write_and_wait at the top of the function into the JDATA state
> clearing block.

IIUC, delalloc and data=journal mode are both mutually exclusive.
So we could get rid of calling filemap_write_and_wait() all together
from ext4_bmap().
And as you pointed filemap_write_and_wait() is called by default in
iomap_bmap which should cover for delalloc case.


@Jan/Darrick,
Could you check if the attached patch looks good. If yes then
will add your Reviewed-by and send a v6.

Thanks for the review!!

-ritesh


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From 93f560d9a483b4f389056e543012d0941734a8f4 Mon Sep 17 00:00:00 2001
From: Ritesh Harjani <riteshh@linux.ibm.com>
Date: Tue, 20 Aug 2019 18:36:33 +0530
Subject: [PATCH 3/6] ext4: Move ext4 bmap to use iomap infrastructure.

ext4_iomap_begin is already implemented which provides ext4_map_blocks,
so just move the API from generic_block_bmap to iomap_bmap for iomap
conversion.

Also no need to call for filemap_write_and_wait() any more in ext4_bmap
since data=journal mode anyway doesn't support delalloc and for all other
cases iomap_bmap() anyway calls the same function, so no need for doing
it twice.

Signed-off-by: Ritesh Harjani <riteshh@linux.ibm.com>
---
 fs/ext4/inode.c | 12 +-----------
 1 file changed, 1 insertion(+), 11 deletions(-)

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 6cf3b969dc86..fac8adbbb3f6 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3174,16 +3174,6 @@ static sector_t ext4_bmap(struct address_space *mapping, sector_t block)
 	if (ext4_has_inline_data(inode))
 		return 0;
 
-	if (mapping_tagged(mapping, PAGECACHE_TAG_DIRTY) &&
-			test_opt(inode->i_sb, DELALLOC)) {
-		/*
-		 * With delalloc we want to sync the file
-		 * so that we can make sure we allocate
-		 * blocks for file
-		 */
-		filemap_write_and_wait(mapping);
-	}
-
 	if (EXT4_JOURNAL(inode) &&
 	    ext4_test_inode_state(inode, EXT4_STATE_JDATA)) {
 		/*
@@ -3214,7 +3204,7 @@ static sector_t ext4_bmap(struct address_space *mapping, sector_t block)
 			return 0;
 	}
 
-	return generic_block_bmap(mapping, block, ext4_get_block);
+	return iomap_bmap(mapping, block, &ext4_iomap_ops);
 }
 
 static int ext4_readpage(struct file *file, struct page *page)
-- 
2.21.0


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