Re: [RFC PATCH] mm: vmscan: avoid anon scanning for GFP_NOIO with low swapcache

[Johannes Weiner]

On Thu, Sep 03, 2026 at 12:01:31PM +0800, Bo Zhang wrote:
> We have observed some cases where memory is allocated with GFP_NOIO, so
> we cannot reclaim any anon folios unless they are in swapcache. We can
> end up spending more than 150 ms looping in `shrink_folio_list()` scanning
> non-swapcache folios without reclaiming a single folio. This is pure
> overhead.

Not entirely. There is some value in aging anon alongside file, so
that the next __GFP_IO reclaimer doesn't look at a stale list.

Can you describe a bit more about what you observed? What workload is
running, maybe you have a stack trace of which NOIO requests are
routinely getting stuck in reclaim?

150ms sounds awful indeed. Is this cumulative for a whole reclaim
cycle or single shrink_folio_list() runs?