[PATCH 1/5] mm: add PSI accounting around ->read_folio and ->readahead calls

[Johannes Weiner]

On Sat, Sep 10, 2022 at 08:50:54AM +0200, Christoph Hellwig wrote:
> PSI tries to account for the cost of bringing back in pages discarded by
> the MM LRU management.  Currently the prime place for that is hooked into
> the bio submission path, which is a rather bad place:
> 
>  - it does not actually account I/O for non-block file systems, of which
>    we have many
>  - it adds overhead and a layering violation to the block layer
> 
> Add the accounting into the two places in the core MM code that read
> pages into an address space by calling into ->read_folio and ->readahead
> so that the entire file system operations are covered, to broaden
> the coverage and allow removing the accounting in the block layer going
> forward.
> 
> As psi_memstall_enter can deal with nested calls this will not lead to
> double accounting even while the bio annotations are still present.
> 
> Signed-off-by: Christoph Hellwig <hch at lst.de>

This is much cleaner. With the fixlet Willy pointed out:

Acked-by: Johannes Weiner <hannes at cmpxchg.org>