Linux-ext4 Archive on lore.kernel.org
 help / color / Atom feed
From: Ritesh Harjani <riteshh@linux.ibm.com>
To: Matthew Bobrowski <mbobrowski@mbobrowski.org>
Cc: tytso@mit.edu, jack@suse.cz, adilger.kernel@dilger.ca,
	linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	hch@infradead.org, david@fromorbit.com, darrick.wong@oracle.com
Subject: Re: [PATCH v4 3/8] ext4: introduce new callback for IOMAP_REPORT operations
Date: Wed, 9 Oct 2019 18:44:40 +0530
Message-ID: <20191009131441.BDE6311C054@d06av25.portsmouth.uk.ibm.com> (raw)
In-Reply-To: <20191009120816.GH14749@poseidon.bobrowski.net>



On 10/9/19 5:38 PM, Matthew Bobrowski wrote:
> On Wed, Oct 09, 2019 at 11:30:21AM +0530, Ritesh Harjani wrote:
>>> +static u16 ext4_iomap_check_delalloc(struct inode *inode,
>>> +				     struct ext4_map_blocks *map)
>>> +{
>>> +	struct extent_status es;
>>> +	ext4_lblk_t end = map->m_lblk + map->m_len - 1;
>>> +
>>> +	ext4_es_find_extent_range(inode, &ext4_es_is_delayed, map->m_lblk,
>>> +				  end, &es);
>>> +
>>> +	/* Entire range is a hole */
>>> +	if (!es.es_len || es.es_lblk > end)
>>> +		return IOMAP_HOLE;
>>> +	if (es.es_lblk <= map->m_lblk) {
>>> +		ext4_lblk_t offset = 0;
>>> +
>>> +		if (es.es_lblk < map->m_lblk)
>>> +			offset = map->m_lblk - es.es_lblk;
>>> +		map->m_lblk = es.es_lblk + offset;
>> This looks redundant no? map->m_lblk never changes actually.
>> So this is not needed here.
> 
> Well, it depends if map->m_lblk == es.es_lblk + offset prior to the
> assignment? If that's always true, then sure, it'd be redundant. But
> honestly, I don't know what the downstream effect would be if this was
> removed. I'd have to look at the code, perform some tests, and figure
> it out.

<snip>
3334         if (es.es_lblk <= map->m_lblk) {
3335                 ext4_lblk_t offset = 0;
3336
3337                 if (es.es_lblk < map->m_lblk)
3338                         offset = map->m_lblk - es.es_lblk;
3339                 map->m_lblk = es.es_lblk + offset;
3340                 map->m_len = es.es_len - offset;
3341                 return IOMAP_DELALLOC;
3342         }

I saw it this way-

In condition "if (es.es_lblk <= map->m_lblk)" there are 2 cases.

Case 1: es.es_lblk is equal to map->m_lblk (equality)
    For this case, "offset" will remain 0.
    So map->lblk = es.es_lblk + 0 (but since es.es_lblk is same as
map->m_lblk in equality case, so it is redundant).


Case 2: es.es_lblk < map->m_lblk (less than)
In this case "offset = map->m_lblk - es.es_lblk"
Now replacing this val of offset in "map->m_lblk = es.es_lblk + offset"
map->m_lblk = es.es_lblk + map->m_lblk - es.es_lblk
which again is map->m_lblk = map->m_lblk - again redundant.


What did I miss?
But sure feel free to test as per your convenience.


> 
>>> +	map.m_lblk = first_block;
>>> +	map.m_len = last_block = first_block + 1;
>>> +	ret = ext4_map_blocks(NULL, inode, &map, 0);
>>> +	if (ret < 0)
>>> +		return ret;
>>> +	if (ret == 0)
>>> +		type = ext4_iomap_check_delalloc(inode, &map);
>>> +	return ext4_set_iomap(inode, iomap, type, first_block, &map);
>> We don't need to send first_block here. Since map->m_lblk
>> is same as first_block.
>> Also with Jan comment, we don't even need 'type' parameter.
>> Then we should be able to rename the function
>> ext4_set_iomap ==> ext4_map_to_iomap. This better reflects what it is
>> doing. Thoughts?
> 
> Depends on what we conclude in 1/8. :)
> 
> I'm for removing 'first_block', but still not convinced removing
> 'type' is heading down the right track if I were to forward think a
> little.

Only once you are convinced that map->m_lblk will not change even in
function ext4_iomap_check_delalloc(), then only you should
drop "first_block" argument from ext4_set_iomap.

Please check above comments once.

-ritesh


  reply index

Thread overview: 47+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-03 11:32 [PATCH v4 0/8] ext4: port direct I/O to iomap infrastructure Matthew Bobrowski
2019-10-03 11:33 ` [PATCH v4 1/8] ext4: move out iomap field population into separate helper Matthew Bobrowski
2019-10-08 10:27   ` Jan Kara
2019-10-09  8:57     ` Matthew Bobrowski
2019-10-09 13:06       ` Jan Kara
2019-10-10  5:39         ` Matthew Bobrowski
2019-10-09  6:02   ` Ritesh Harjani
2019-10-09  7:07     ` Christoph Hellwig
2019-10-09  7:50       ` Ritesh Harjani
2019-10-09  9:09         ` Matthew Bobrowski
2019-10-03 11:33 ` [PATCH v4 2/8] ext4: move out IOMAP_WRITE path " Matthew Bobrowski
2019-10-08 10:31   ` Jan Kara
2019-10-09  9:18     ` Matthew Bobrowski
2019-10-09  6:22   ` Ritesh Harjani
2019-10-09  9:31     ` Matthew Bobrowski
2019-10-03 11:33 ` [PATCH v4 3/8] ext4: introduce new callback for IOMAP_REPORT operations Matthew Bobrowski
2019-10-08 10:42   ` Jan Kara
2019-10-09  9:41     ` Matthew Bobrowski
2019-10-09  6:00   ` Ritesh Harjani
2019-10-09 12:08     ` Matthew Bobrowski
2019-10-09 13:14       ` Ritesh Harjani [this message]
2019-10-03 11:34 ` [PATCH v4 4/8] ext4: introduce direct I/O read path using iomap infrastructure Matthew Bobrowski
2019-10-08 10:52   ` Jan Kara
2019-10-09 10:55     ` Matthew Bobrowski
2019-10-09  6:39   ` Ritesh Harjani
2019-10-03 11:34 ` [PATCH v4 5/8] ext4: move inode extension/truncate code out from ->iomap_end() callback Matthew Bobrowski
2019-10-08 11:25   ` Jan Kara
2019-10-09 10:18     ` Matthew Bobrowski
2019-10-09 12:51       ` Jan Kara
2019-10-10  5:44         ` Matthew Bobrowski
2019-10-09  6:27   ` Ritesh Harjani
2019-10-09 10:20     ` Matthew Bobrowski
2019-10-03 11:34 ` [PATCH v4 6/8] ext4: move inode extension checks out from ext4_iomap_alloc() Matthew Bobrowski
2019-10-08 11:27   ` Jan Kara
2019-10-09 10:21     ` Matthew Bobrowski
2019-10-09  6:30   ` Ritesh Harjani
2019-10-09 10:39     ` Matthew Bobrowski
2019-10-03 11:34 ` [PATCH v4 7/8] ext4: reorder map.m_flags checks in ext4_set_iomap() Matthew Bobrowski
2019-10-08 11:30   ` Jan Kara
2019-10-09 10:42     ` Matthew Bobrowski
2019-10-09  6:35   ` Ritesh Harjani
2019-10-09 10:43     ` Matthew Bobrowski
2019-10-03 11:35 ` [PATCH v4 8/8] ext4: introduce direct I/O write path using iomap infrastructure Matthew Bobrowski
2019-10-08 15:12   ` Jan Kara
2019-10-09  7:11     ` Christoph Hellwig
2019-10-09 13:41       ` Jan Kara
2019-10-09 11:53     ` Matthew Bobrowski

Reply instructions:

You may reply publically to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20191009131441.BDE6311C054@d06av25.portsmouth.uk.ibm.com \
    --to=riteshh@linux.ibm.com \
    --cc=adilger.kernel@dilger.ca \
    --cc=darrick.wong@oracle.com \
    --cc=david@fromorbit.com \
    --cc=hch@infradead.org \
    --cc=jack@suse.cz \
    --cc=linux-ext4@vger.kernel.org \
    --cc=linux-fsdevel@vger.kernel.org \
    --cc=mbobrowski@mbobrowski.org \
    --cc=tytso@mit.edu \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

Linux-ext4 Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-ext4/0 linux-ext4/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-ext4 linux-ext4/ https://lore.kernel.org/linux-ext4 \
		linux-ext4@vger.kernel.org
	public-inbox-index linux-ext4

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-ext4


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git