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From: Nikolay Borisov <nborisov@suse.com>
To: Jeff Mahoney <jeffm@suse.com>,
	dsterba@suse.cz, linux-btrfs@vger.kernel.org
Subject: Re: [PATCH 01/15] btrfs: Honour FITRIM range constraints during free space trim
Date: Thu, 31 Jan 2019 23:45:25 +0200
Message-ID: <a0a93777-f02e-cc73-6bcd-61116247ea8b@suse.com> (raw)
In-Reply-To: <5fd4c23c-3716-50bf-256f-1078243169da@suse.com>



On 31.01.19 г. 21:30 ч., Jeff Mahoney wrote:
> On 1/31/19 10:35 AM, Nikolay Borisov wrote:
>>
>>
>> On 31.01.19 г. 17:21 ч., David Sterba wrote:
>>> On Wed, Jan 30, 2019 at 04:50:48PM +0200, Nikolay Borisov wrote:
>>>> Up until know trimming the freespace was done irrespective of what the
>>>> arguments of the FITRIM ioctl were. For example fstrim's -o/-l arguments
>>>> will be entirely ignored. Fix it by correctly handling those paramter.
>>>> This requires breaking if the found freespace extent is after the end
>>>> of the passed range as well as completing trim after trimming
>>>> fstrim_range::len bytes.
>>>
>>> How does this work with with multipe-device filesystems? The fstrim
>>> range would apply to all of them. Which does make some sense, though
>>> might be unexpected as this does not happen for other filesystems.
>>
>> Well FITRIM doesn't have support for multiple device so it's to the
>> discretion of the fs how exactly this is implemented. And this is indeed
>> the way things work currently.
>>
>>>
>>> The FITRIM range is in the physical coordinates, so eg. the taking the
>>> maximum size of all devices and iterating over that by 1GiB steps would
>>> go though the whole filesystem. Something to put to the changelog and
>>> documentation.
>>
>> I don't follow, trimming would just trim the physical range as passed by
>> fstrim -o/-l options. That 1gb value is not hardcoded anywhere. If
>> someone wants to trim all of the freespace (which is what the majority
>> of the user do) then they can run FITRIM with 0 for offset and -1 for
>> length.
> 
> But what does physical range mean in this context?  The address space
> presented to the user and which FITRIM operates on is the logical
> address space that the extent tree uses.  For allocated chunks, there's
> a mapping to physical devices.  It can have holes in it.  What does it
> mean when that offset/length hits a hole?

Physical in this context mean the actual space on the disk themselves.
This really has repercussion when trimming freespace. So for example when

fstrim -o 50m -l 20g is run this means that all space between 50m and
20g in the block groups (logical free space) will be trimmed.
Additionally, the physical (that is the space on the actual devices)
will also be trimmed. I don't think we can avoid this.

> 
> I'm okay with (0,-1) referring to all the space on all devices.  That
> seems obvious enough.  Perhaps for bounded trims, it only applies to the
> parts within the range that are allocated?
> 
> -Jeff
> 
> 
>>>> Fixes: 499f377f49f0 ("btrfs: iterate over unused chunk space in FITRIM")
>>>> Signed-off-by: Nikolay Borisov <nborisov@suse.com>
>>>> ---
>>>>  fs/btrfs/extent-tree.c | 25 +++++++++++++++++++------
>>>>  1 file changed, 19 insertions(+), 6 deletions(-)
>>>>
>>>> diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
>>>> index 1fdba38761f7..fc3f6acc3c9b 100644
>>>> --- a/fs/btrfs/extent-tree.c
>>>> +++ b/fs/btrfs/extent-tree.c
>>>> @@ -11190,9 +11190,9 @@ int btrfs_error_unpin_extent_range(struct btrfs_fs_info *fs_info,
>>>>   * held back allocations.
>>>>   */
>>>>  static int btrfs_trim_free_extents(struct btrfs_device *device,
>>>> -				   u64 minlen, u64 *trimmed)
>>>> +				   struct fstrim_range *range, u64 *trimmed)
>>>>  {
>>>> -	u64 start = 0, len = 0;
>>>> +	u64 start = range->start, len = 0;
>>>>  	int ret;
>>>>  
>>>>  	*trimmed = 0;
>>>> @@ -11235,8 +11235,8 @@ static int btrfs_trim_free_extents(struct btrfs_device *device,
>>>>  		if (!trans)
>>>>  			up_read(&fs_info->commit_root_sem);
>>>>  
>>>> -		ret = find_free_dev_extent_start(trans, device, minlen, start,
>>>> -						 &start, &len);
>>>> +		ret = find_free_dev_extent_start(trans, device, range->minlen,
>>>> +						 start, &start, &len);
>>>>  		if (trans) {
>>>>  			up_read(&fs_info->commit_root_sem);
>>>>  			btrfs_put_transaction(trans);
>>>> @@ -11249,6 +11249,16 @@ static int btrfs_trim_free_extents(struct btrfs_device *device,
>>>>  			break;
>>>>  		}
>>>>  
>>>> +		/* If we are out of the passed range break */
>>>> +		if (start > range->start + range->len - 1) {
>>>> +			mutex_unlock(&fs_info->chunk_mutex);
>>>> +			ret = 0;
>>>> +			break;
>>>> +		}
>>>> +
>>>> +		start = max(range->start, start);
>>>> +		len = min(range->len, len);
>>>> +
>>>>  		ret = btrfs_issue_discard(device->bdev, start, len, &bytes);
>>>>  		mutex_unlock(&fs_info->chunk_mutex);
>>>>  
>>>> @@ -11258,6 +11268,10 @@ static int btrfs_trim_free_extents(struct btrfs_device *device,
>>>>  		start += len;
>>>>  		*trimmed += bytes;
>>>>  
>>>> +		/* We've trimmed enough */
>>>> +		if (*trimmed >= range->len)
>>>> +			break;
>>>> +
>>>>  		if (fatal_signal_pending(current)) {
>>>>  			ret = -ERESTARTSYS;
>>>>  			break;
>>>> @@ -11341,8 +11355,7 @@ int btrfs_trim_fs(struct btrfs_fs_info *fs_info, struct fstrim_range *range)
>>>>  	mutex_lock(&fs_info->fs_devices->device_list_mutex);
>>>>  	devices = &fs_info->fs_devices->devices;
>>>>  	list_for_each_entry(device, devices, dev_list) {
>>>> -		ret = btrfs_trim_free_extents(device, range->minlen,
>>>> -					      &group_trimmed);
>>>> +		ret = btrfs_trim_free_extents(device, range, &group_trimmed);
>>>>  		if (ret) {
>>>>  			dev_failed++;
>>>>  			dev_ret = ret;
>>>> -- 
>>>> 2.17.1
>>
> 
> 

  reply index

Thread overview: 36+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-01-30 14:50 [PATCH 00/15] Improvements to fitrim Nikolay Borisov
2019-01-30 14:50 ` [PATCH 01/15] btrfs: Honour FITRIM range constraints during free space trim Nikolay Borisov
2019-01-31 15:21   ` David Sterba
2019-01-31 15:35     ` Nikolay Borisov
2019-01-31 15:48       ` David Sterba
2019-01-31 19:30       ` Jeff Mahoney
2019-01-31 21:45         ` Nikolay Borisov [this message]
2019-01-30 14:50 ` [PATCH 02/15] btrfs: Make WARN_ON in a canonical form Nikolay Borisov
2019-01-31 15:22   ` David Sterba
2019-02-04 13:12   ` Johannes Thumshirn
2019-01-30 14:50 ` [PATCH 03/15] btrfs: Remove EXTENT_FIRST_DELALLOC bit Nikolay Borisov
2019-01-31 15:23   ` David Sterba
2019-02-04 13:15   ` Johannes Thumshirn
2019-01-30 14:50 ` [PATCH 04/15] btrfs: combine device update operations during transaction commit Nikolay Borisov
2019-02-04 13:25   ` Johannes Thumshirn
2019-02-04 14:48     ` Nikolay Borisov
2019-02-05  9:21       ` Johannes Thumshirn
2019-01-30 14:50 ` [PATCH 05/15] btrfs: Handle pending/pinned chunks before blockgroup relocation during device shrink Nikolay Borisov
2019-02-04 13:29   ` Johannes Thumshirn
2019-01-30 14:50 ` [PATCH 06/15] btrfs: Rename and export clear_btree_io_tree Nikolay Borisov
2019-02-04 13:31   ` Johannes Thumshirn
2019-01-30 14:50 ` [PATCH 07/15] btrfs: Populate ->orig_block_len during read_one_chunk Nikolay Borisov
2019-01-30 14:50 ` [PATCH 08/15] btrfs: Introduce new bits for device allocation tree Nikolay Borisov
2019-01-30 14:50 ` [PATCH 09/15] btrfs: replace pending/pinned chunks lists with io tree Nikolay Borisov
2019-01-30 14:50 ` [PATCH 10/15] btrfs: Remove 'trans' argument from find_free_dev_extent(_start) Nikolay Borisov
2019-02-04 14:36   ` Johannes Thumshirn
2019-01-30 14:50 ` [PATCH 11/15] btrfs: Factor out in_range macro Nikolay Borisov
2019-02-04 13:57   ` Johannes Thumshirn
2019-01-30 14:50 ` [PATCH 12/15] btrfs: Optimize unallocated chunks discard Nikolay Borisov
2019-01-30 14:51 ` [PATCH 13/15] btrfs: Fix gross misnaming Nikolay Borisov
2019-01-30 14:51 ` [PATCH 14/15] btrfs: Implement find_first_clear_extent_bit Nikolay Borisov
2019-02-04 14:04   ` Johannes Thumshirn
2019-02-04 16:57   ` Nikolay Borisov
2019-01-30 14:51 ` [PATCH 15/15] btrfs: Switch btrfs_trim_free_extents to find_first_clear_extent_bit Nikolay Borisov
2019-01-31 15:38   ` [PATCH v2] " Nikolay Borisov
2019-01-31 15:41   ` [PATCH v3] " Nikolay Borisov

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