Re: [PATCH] btrfs: fix u32 to s64 type conversion in dirty_metadata_bytes accounting

[Dave Chen <davechen@synology.com>]

On Mon, Jun 29, 2026 at 01:08:05PM +0100, Filipe Manana wrote:
> Curious, do you have any performance data to give an idea of the impact?
>
> I'm asking not only for clarity but also to determine if adding a
> Fixes tag for stable backports makes sense.

We don't have upstream performance benchmark data for this.  We
discovered the issue while debugging an unrelated internal bug —
dirty_metadata_bytes had grown to petabyte-range values on a filesystem
with a fraction of that in actual dirty metadata, which led us to trace
it back to the u32 negation.

The writeback impact described in the commit message
(balance_dirty_pages_ratelimited() being called unconditionally) is
based on code analysis, not measured.

I'll leave the Fixes tag decision to you and David.

Thanks for the review.


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