linux-kernel - Re: [PATCH v2 07/12] s390: add pte_free

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Date:   Wed, 28 Jun 2023 22:08:08 -0700 (PDT)
From:   Hugh Dickins <hughd@...gle.com>
To:     Gerald Schaefer <gerald.schaefer@...ux.ibm.com>
cc:     Hugh Dickins <hughd@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Mike Rapoport <rppt@...nel.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Matthew Wilcox <willy@...radead.org>,
        David Hildenbrand <david@...hat.com>,
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        Peter Xu <peterx@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Will Deacon <will@...nel.org>, Yu Zhao <yuzhao@...gle.com>,
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        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v2 07/12] s390: add pte_free_defer() for pgtables sharing
 page

On Wed, 28 Jun 2023, Gerald Schaefer wrote:
> 
> As discussed in the other thread, we would rather go with less complexity,
> possibly switching to an approach w/o the list and fragment re-use in the
> future. For now, as a first step in that direction, we can try with not
> adding fragments back only for pte_free_defer(). Here is an adjusted
> version of your patch, copying most of your pte_free_defer() logic and
> also description, tested with LTP and all three of your patch series applied:

Thanks, Gerald: I don't mind abandoning my 13/12 SLAB_TYPESAFE_BY_RCU
patch (posted with fewer Cc's to the s390 list last week), and switching
to your simpler who-cares-if-we-sometimes-don't-make-maximal-use-of-page
patch.

But I didn't get deep enough into it today to confirm it - and disappointed
that you've found it necessary to play with pt_frag_refcount in addition to
_refcount and HH bits.  No real problem with that, but my instinct says it
should be simpler.

Tomorrow...
Hugh