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[79.242.59.82]) by smtp.gmail.com with ESMTPSA id l20sm7862599wmq.42.2021.10.28.08.54.02 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 28 Oct 2021 08:54:02 -0700 (PDT) Message-ID: <53abed4c-a66b-9735-4411-c919ede8c47c@redhat.com> Date: Thu, 28 Oct 2021 17:54:01 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.1.0 Subject: Re: [PATCH] mm: Disable NUMA_BALANCING_DEFAULT_ENABLED and TRANSPARENT_HUGEPAGE on PREEMPT_RT To: Sebastian Andrzej Siewior , Andrew Morton , Mel Gorman Cc: linux-mm@kvack.org, Vlastimil Babka , Peter Zijlstra , Thomas Gleixner References: <20211028143327.hfbxjze7palrpfgp@linutronix.de> From: David Hildenbrand Organization: Red Hat In-Reply-To: <20211028143327.hfbxjze7palrpfgp@linutronix.de> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 9C238F0000A7 X-Stat-Signature: yh5c7xacnbiptck5xqpkaqtw1nh3siqb Authentication-Results: imf16.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=ArkHVEuk; dmarc=pass (policy=none) header.from=redhat.com; spf=none (imf16.hostedemail.com: domain of david@redhat.com has no SPF policy when checking 216.205.24.124) smtp.mailfrom=david@redhat.com X-HE-Tag: 1635436440-710533 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 28.10.21 16:33, Sebastian Andrzej Siewior wrote: > TRANSPARENT_HUGEPAGE: > There are potential non-deterministic delays to an RT thread if a critical > memory region is not THP-aligned and a non-RT buffer is located in the same > hugepage-aligned region. It's also possible for an unrelated thread to migrate > pages belonging to an RT task incurring unexpected page faults due to memory > defragmentation even if khugepaged is disabled. > > Regular HUGEPAGEs are not affected by this can be used. > > NUMA_BALANCING: > There is a non-deterministic delay to mark PTEs PROT_NONE to gather NUMA fault > samples, increased page faults of regions even if mlocked and non-deterministic > delays when migrating pages. > > [Mel Gorman worded 99% of the commit description]. > > Link: https://lore.kernel.org/all/20200304091159.GN3818@techsingularity.net/ > Link: https://lore.kernel.org/all/20211026165100.ahz5bkx44lrrw5pt@linutronix.de/ > Cc: Mel Gorman > Signed-off-by: Sebastian Andrzej Siewior > --- > init/Kconfig | 2 +- > mm/Kconfig | 2 +- > 2 files changed, 2 insertions(+), 2 deletions(-) > > diff --git a/init/Kconfig b/init/Kconfig > index edc0a0228f143..f83e7a0478f7c 100644 > --- a/init/Kconfig > +++ b/init/Kconfig > @@ -911,7 +911,7 @@ config NUMA_BALANCING > bool "Memory placement aware NUMA scheduler" > depends on ARCH_SUPPORTS_NUMA_BALANCING > depends on !ARCH_WANT_NUMA_VARIABLE_LOCALITY > - depends on SMP && NUMA && MIGRATION > + depends on SMP && NUMA && MIGRATION && !PREEMPT_RT > help > This option adds support for automatic NUMA aware memory/task placement. > The mechanism is quite primitive and is based on migrating memory when > diff --git a/mm/Kconfig b/mm/Kconfig > index c150a0c6fce2c..5c5508fafcec5 100644 > --- a/mm/Kconfig > +++ b/mm/Kconfig > @@ -374,7 +374,7 @@ config NOMMU_INITIAL_TRIM_EXCESS > > config TRANSPARENT_HUGEPAGE > bool "Transparent Hugepage Support" > - depends on HAVE_ARCH_TRANSPARENT_HUGEPAGE > + depends on HAVE_ARCH_TRANSPARENT_HUGEPAGE && !PREEMPT_RT > select COMPACTION > select XARRAY_MULTI > help > Makes perfect sense to me. I was also wondering how "dangerous" MIGRATION (and everything depending on it, like CMA, compaction, MEMORY_HOTREMOVE, ...) is for RT recently. Reviewed-by: David Hildenbrand -- Thanks, David / dhildenb