lkml.org 
[lkml]   [2024]   [May]   [16]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
SubjectRe: [PATCH 3/5] dm: support retrieving struct dm_target from struct dm_dev
From
On 2024/5/15 23:42, Benjamin Marzinski wrote:
> On Tue, May 14, 2024 at 05:04:42PM +0800, Yang Yang wrote:
>> Add a list to the struct dm_dev structure to store the associated
>> targets, while also allowing differentiation between different target
>> types.
>
> I still think this is more complex than it needs to be. If devices that
> support flush_pass_around can guarantee that:
>
> 1. They will send a flush bio to all of their table devices
> 2. They are fine with another target sending the flush bio to their
> table devices
>
> Then I don't see why we need the table devices to keep track of all the
> different target types that are using them. Am I missing something here?

I attempted to enhance this solution to support additional target types,
such as those with num_flush_bios greater than 1.

> If we don't need to worry about sending a flush bio to a target of each
> type that is using a table device, then all we need to do is call
> __send_empty_flush_bios() for enough targets to cover all the table
> devices. This seems a lot easier to track. We just need another flag in
> dm_target, something like sends_pass_around_flush.
>
> When a target calls dm_get_device(), if it adds a new table device to
> t->devices, then it's the first target in this table to use that device.
> If flush_pass_around is set for this target, then it also sets
> sends_pass_around_flush. In __send_empty_flush() if the table has
> flush_pass_around set, when you iterate through the devices, you only
> call __send_empty_flush_bios() for the ones with sends_pass_around_flush
> set.
>
> Or am I overlooking something?

If I understand correctly, you are suggesting to iterate through all the
targets, handling those with sends_pass_around_flush set, and skipping
those where sends_pass_around_flush is not set. I believe this approach
may result in some CPU wastage.

for i in {0..1023}; do
echo $((8000*$i)) 8000 linear /dev/sda2 $((16384*$i))
done | sudo dmsetup create example

In this specific scenario, a single iteration of the loop is all that
is needed.

>
> -Ben
>
>>
>> Signed-off-by: Yang Yang <yang.yang@vivo.com>
>> ---
>> drivers/md/dm-table.c | 36 +++++++++++++++++++++++++++++++++++
>> include/linux/device-mapper.h | 3 +++
>> 2 files changed, 39 insertions(+)
>>
>> diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
>> index bd68af10afed..f6554590b7af 100644
>> --- a/drivers/md/dm-table.c
>> +++ b/drivers/md/dm-table.c
>> @@ -741,6 +741,8 @@ int dm_table_add_target(struct dm_table *t, const char *type,
>> if (ti->flush_pass_around == 0)
>> t->flush_pass_around = 0;
>>
>> + INIT_LIST_HEAD(&ti->list);
>> +
>> return 0;
>>
>> bad:
>> @@ -2134,6 +2136,25 @@ void dm_table_postsuspend_targets(struct dm_table *t)
>> suspend_targets(t, POSTSUSPEND);
>> }
>>
>> +static int dm_link_dev_to_target(struct dm_target *ti, struct dm_dev *dev,
>> + sector_t start, sector_t len, void *data)
>> +{
>> + struct list_head *targets = &dev->targets;
>> + struct dm_target *pti;
>> +
>> + if (!list_empty(targets)) {
>> + list_for_each_entry(pti, targets, list) {
>> + if (pti->type == ti->type)
>> + return 0;
>> + }
>> + }
>> +
>> + if (list_empty(&ti->list))
>> + list_add_tail(&ti->list, targets);
>> +
>> + return 0;
>> +}
>> +
>> int dm_table_resume_targets(struct dm_table *t)
>> {
>> unsigned int i;
>> @@ -2162,6 +2183,21 @@ int dm_table_resume_targets(struct dm_table *t)
>> ti->type->resume(ti);
>> }
>>
>> + if (t->flush_pass_around) {
>> + struct list_head *devices = &t->devices;
>> + struct dm_dev_internal *dd;
>> +
>> + list_for_each_entry(dd, devices, list)
>> + INIT_LIST_HEAD(&dd->dm_dev->targets);
>> +
>> + for (i = 0; i < t->num_targets; i++) {
>> + struct dm_target *ti = dm_table_get_target(t, i);
>> +
>> + if (ti->type->iterate_devices)
>> + ti->type->iterate_devices(ti, dm_link_dev_to_target, NULL);
>> + }
>> + }
>> +
>> return 0;
>> }
>>
>> diff --git a/include/linux/device-mapper.h b/include/linux/device-mapper.h
>> index 0893ff8c01b6..19e03f9b2589 100644
>> --- a/include/linux/device-mapper.h
>> +++ b/include/linux/device-mapper.h
>> @@ -169,6 +169,7 @@ struct dm_dev {
>> struct dax_device *dax_dev;
>> blk_mode_t mode;
>> char name[16];
>> + struct list_head targets;
>> };
>>
>> /*
>> @@ -298,6 +299,8 @@ struct dm_target {
>> struct dm_table *table;
>> struct target_type *type;
>>
>> + struct list_head list;
>> +
>> /* target limits */
>> sector_t begin;
>> sector_t len;
>> --
>> 2.34.1
>>
>


\
 
 \ /
  Last update: 2024-05-27 18:29    [W:0.107 / U:1.256 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site