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

Johannes Weiner
2022-09-14T11:41:48Z

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@lst.de>

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

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