linux-kernel - Re: [PATCH 07/12] s390: add pte_free_defer(), with use of mmdrop

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Message-ID: <ed24b58f-ef9f-2427-7372-5c77378c5b40@google.com>
Date:   Wed, 7 Jun 2023 19:46:26 -0700 (PDT)
From:   Hugh Dickins <hughd@...gle.com>
To:     Jason Gunthorpe <jgg@...pe.ca>
cc:     Hugh Dickins <hughd@...gle.com>,
        Gerald Schaefer <gerald.schaefer@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Mike Rapoport <rppt@...nel.org>,
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        Mel Gorman <mgorman@...hsingularity.net>,
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        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 07/12] s390: add pte_free_defer(), with use of
 mmdrop_async()

On Tue, 6 Jun 2023, Jason Gunthorpe wrote:
> On Mon, Jun 05, 2023 at 10:11:52PM -0700, Hugh Dickins wrote:
> 
> > "deposited" pagetable fragments, over in arch/s390/mm/pgtable.c: use
> > the first two longs of the page table itself for threading the list.
> 
> It is not RCU anymore if it writes to the page table itself before the
> grace period, so this change seems to break the RCU behavior of
> page_table_free_rcu().. The rcu sync is inside tlb_remove_table()
> called after the stores.

Yes indeed, thanks for pointing that out.

> 
> Maybe something like an xarray on the mm to hold the frags?

I think we can manage without that:
I'll say slightly more in reply to Gerald.

Hugh