Re: [PATCH v2] btrfs: Limit size of bios submitted from writeback

[Qu Wenruo <quwenruo.btrfs@gmx.com>]

在 2026/4/27 19:20, Qu Wenruo 写道:
[...]
>> Yeah, at this point I'm not sure the complexity is worth it. Normally 
>> added
>> disks have very similar parameters as existing ones, also even if they 
>> are
>> somewhat different, it will cost you a few percent of writeback speed at
>> worst which doesn't seem too bad and it will "fix" itself on next mount.
> 
> Thanks, we're on the same page.
> 
> Now the patch is pushed to for-next branch, with one typo "miliseconds" 
> fixed.
> 
> Thanks,
> Qu

Just a minor update.

The existing check is considering device->bdev always exists, but we can 
have missing devices which doesn't have device->bdev, and this will 
cause NULL pointer dereference during test cases like btrfs/027.

Fixed in for-next branch with the following small diff:

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 8d36e8a9f0d9..93a923e4ecaf 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -8224,6 +8224,8 @@ int btrfs_init_writeback_bio_size(struct 
btrfs_fs_info *fs_info)
                 struct request_queue *queue;
                 unsigned int io_opt;

+               if (!device->bdev || test_bit(BTRFS_DEV_STATE_MISSING, 
&device->dev_state))
+                       continue;
                 queue = bdev_get_queue(device->bdev);
                 io_opt = queue_io_opt(queue) ? :
                                 queue_max_sectors(queue) << SECTOR_SHIFT;

Thanks,
Qu
>>
>>                                 Honza
> 
>