[PATCH v3 03/34] s390: Use pt_frag_refcount for pagetables

Gerald Schaefer gerald.schaefer at linux.ibm.com
Thu Jun 1 23:19:00 AEST 2023

 On Wed, 31 May 2023 14:30:01 -0700
"Vishal Moola (Oracle)" <vishal.moola at gmail.com> wrote:

> s390 currently uses _refcount to identify fragmented page tables.
> The page table struct already has a member pt_frag_refcount used by
> powerpc, so have s390 use that instead of the _refcount field as well.
> This improves the safety for _refcount and the page table tracking.
> This also allows us to simplify the tracking since we can once again use
> the lower byte of pt_frag_refcount instead of the upper byte of _refcount.

This would conflict with s390 impact of pte_free_defer() work from Hugh Dickins

There he uses pt_frag_refcount, or rather pt_mm in the same union, to save
the mm_struct for deferred pte_free().

I still need to look closer into both of your patch series, but so far it
seems that you have no hard functional requirement to switch from _refcount
to pt_frag_refcount here, for s390.

If this is correct, and you do not e.g. need this to make some other use
of _refcount, I would suggest to drop this patch.

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