Re: [Question] why not flush device cache at _vg_commit_raw

On 1/24/24 21:13, Anthony Iliopoulos wrote:
> On Wed, Jan 24, 2024 at 01:35:49PM +0100, Zdenek Kabelac wrote:
>> I guess our dev_flush() function is mostly handling all those cases properly
>> with the use of  ioctl(BLKFLSBUF).
> 
> This ioctl by itself will only flush the page cache and not device
> caches, but it is indeed followed by a fsync on the blockdev which is
> basically the only way for userspace to trigger a device cache flush
> when operating directly on a block device.
> 
>> The only problem is - it's usage somehow vanished - and even in the past
>> it's been  basically used only for non-direct usage so likely still not
>> correct.
> 
> Indeed, the device cache flushing is required for data integrity
> irrespective of the io mode (unless O_DSYNC/RWF_DSYNC), direct-io only
> obviates the need for flushing the page cache.
> 

In my view, vg_commit() is a good place to call dev_flush(). This could
only affect (important) metadata IOs, make all write IOs to persistent
storage ASAP.

Thanks,
Heming