linux-kernel - Re: [v2 PATCH 2/2] powerpc/64s/radix: don't need to broadcast IPI for radix pmd collapse flush

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Date:   Wed, 7 Sep 2022 16:12:16 -0400
From:   Peter Xu <peterx@...hat.com>
To:     Yang Shi <shy828301@...il.com>
Cc:     david@...hat.com, kirill.shutemov@...ux.intel.com,
        jhubbard@...dia.com, jgg@...dia.com, hughd@...gle.com,
        akpm@...ux-foundation.org, aneesh.kumar@...ux.ibm.com,
        linux-mm@...ck.org, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org
Subject: Re: [v2 PATCH 2/2] powerpc/64s/radix: don't need to broadcast IPI
 for radix pmd collapse flush

On Wed, Sep 07, 2022 at 11:01:44AM -0700, Yang Shi wrote:
> The IPI broadcast is used to serialize against fast-GUP, but fast-GUP
> will move to use RCU instead of disabling local interrupts in fast-GUP.
> Using an IPI is the old-styled way of serializing against fast-GUP
> although it still works as expected now.
> 
> And fast-GUP now fixed the potential race with THP collapse by checking
> whether PMD is changed or not.  So IPI broadcast in radix pmd collapse
> flush is not necessary anymore.  But it is still needed for hash TLB.
> 
> Suggested-by: Aneesh Kumar K.V <aneesh.kumar@...ux.ibm.com>
> Signed-off-by: Yang Shi <shy828301@...il.com>

Acked-by: Peter Xu <peterx@...hat.com>

-- 
Peter Xu