Re: [PATCH] block/psi: make PSI annotations of submit_bio only work for file pages

[Christoph Hellwig]

On Wed, Mar 30, 2022 at 12:17:09PM -0400, Johannes Weiner wrote:
> It's add_to_page_cache_lru() that sets the flag.
> 
> Basically, when a PageWorkingset (hot) page gets reclaimed, the bit is
> stored in the vacated tree slot. When the entry is brought back in,
> add_to_page_cache_lru() transfers it to the newly allocated page.

Ok.  In this case my patch didn't quite do the right thing for readahead
either.  But that does leave a question for the btrfs compressed
case, which only adds extra pages to a read to readahad a bigger
cluster size - that is these pages are not read at the request of the
VM.  Does it really make sense to do PSI accounting for them in that
case?