Re: [PATCH -RFC 0/2] mm/ext4: avoid data corruption when extending DIO write race with buffered read

Christoph Hellwig
2023-12-06T12:20:18Z

On Wed, Dec 06, 2023 at 09:34:49PM +1100, Dave Chinner wrote:
> Largely they were performance problems - unpredictable IO latency
> and CPU overhead for IO meant applications would randomly miss SLAs.
> The application would see IO suddenly lose all concurrency, go real
> slow and/or burn lots more CPU when the inode switched to buffered
> mode.
>
> I'm not sure that's a particularly viable model given the raw IO
> throughput even cheap modern SSDs largely exceeds the capability of
> buffered IO through the page cache. The differences in concurrency,
> latency and throughput between buffered and DIO modes will be even
> more stark itoday than they were 20 years ago....

The question is what's worse: random performance drops or random
corruption. I suspect the former is less bad, especially if we have
good tracepoints to pin it down.