Re: [PATCH v4] mm, compaction: Skip all non-migratable pages during scan

[Andrew Morton]

On Tue, 30 May 2023 09:42:33 -0600 Khalid Aziz <khalid.aziz@xxxxxxxxxx> wrote:

> > I completely agree that we should be careful with such mapcount vs. pagecount checks, and if we can use something 
> > better, let's use something *better*.
> 
> When we have a reliable folio_maybe_dma_longterm_pinned() function, it will be better to call that instead of doing 
> refcount vs mapcount check. Until that better function to check for pinned pages is in place, may I propose that the 
> current patch fixes a customer problem though not optimally and is a good enough working solution. When a better 
> function is in place, page_has_extra_refs() function can be updated to rely on this other function instead of refcount 
> vs mapcount.

We seem rather stuck with this patch.  I think I'll drop it while we
ponder a way forward.