From: Christian Borntraeger <borntraeger@linux.ibm.com>
To: Alexander Gordeev <agordeev@linux.ibm.com>,
Heiko Carstens <hca@linux.ibm.com>
Cc: Kevin Brodsky <kevin.brodsky@arm.com>,
David Hildenbrand <david@redhat.com>,
Andrew Morton <akpm@linux-foundation.org>,
Gerald Schaefer <gerald.schaefer@linux.ibm.com>,
Vasily Gorbik <gor@linux.ibm.com>,
Claudio Imbrenda <imbrenda@linux.ibm.com>,
linux-s390@vger.kernel.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 6/6] s390/mm: Allow lazy MMU mode disabling
Date: Thu, 16 Apr 2026 10:22:11 +0200 [thread overview]
Message-ID: <161ab40c-dad7-42b4-b6ad-917f8249254a@linux.ibm.com> (raw)
In-Reply-To: <2a497bff-1773-4245-a63c-784ed8853b11-agordeev@linux.ibm.com>
Am 16.04.26 um 09:00 schrieb Alexander Gordeev:
> On Thu, Apr 16, 2026 at 07:44:05AM +0200, Heiko Carstens wrote:
>>> @@ -169,6 +185,8 @@ void arch_enter_lazy_mmu_mode_for_pte_range(struct mm_struct *mm,
>>> {
>>> if (!test_facility(13))
>>> return;
>>> + if (!static_branch_likely(&lazy_mmu))
>>> + return;
>>
>> Looks like there is an alternative chicken switch available: remove
>> facility bit 13 from the facility list via kernel command line option.
>>
>> Unless I am mistaken: that should be sufficient and avoids adding more
>> code.
>
> But that would also withdraw multi-IPTE from other unrelated parts of
> the code, e.g. from __kernel_map_pages().
Which is fine. Do not over-optimize for a case that should not be
needed unless we really mess up. This parameter is way too complicated to ever
be set/unset by a customer.
prev parent reply other threads:[~2026-04-16 8:22 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-04-15 15:01 [PATCH v2 0/6] s390/mm: Batch PTE updates in lazy MMU mode Alexander Gordeev
2026-04-15 15:01 ` [PATCH v2 1/6] mm: Make lazy MMU mode context-aware Alexander Gordeev
2026-04-15 15:01 ` [PATCH v2 2/6] mm/pgtable: Fix bogus comment to clear_not_present_full_ptes() Alexander Gordeev
2026-04-16 7:58 ` David Hildenbrand (Arm)
2026-04-16 8:53 ` Alexander Gordeev
2026-04-15 15:01 ` [PATCH v2 3/6] s390/mm: Complete ptep_get() conversion Alexander Gordeev
2026-04-15 15:01 ` [PATCH v2 4/6] s390/mm: Make PTC and UV call order consistent Alexander Gordeev
2026-04-15 15:01 ` [PATCH v2 5/6] s390/mm: Batch PTE updates in lazy MMU mode Alexander Gordeev
2026-04-16 5:40 ` Heiko Carstens
2026-04-16 5:51 ` Alexander Gordeev
2026-04-15 15:01 ` [PATCH v2 6/6] s390/mm: Allow lazy MMU mode disabling Alexander Gordeev
2026-04-16 5:44 ` Heiko Carstens
2026-04-16 7:00 ` Alexander Gordeev
2026-04-16 8:22 ` Christian Borntraeger [this message]
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