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[173.79.60.52]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-907ba8b5d70sm54929666d6.4.2026.07.23.15.56.40 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 23 Jul 2026 15:56:41 -0700 (PDT) Date: Thu, 23 Jul 2026 18:56:36 -0400 From: Gregory Price To: Yosry Ahmed Cc: Johannes Weiner , Sean Christopherson , Yan Zhao , pbonzini@redhat.com, Andrew Morton , David Hildenbrand , Zi Yan , Matthew Brost , Joshua Hahn , Rakie Kim , Byungchul Park , Ying Huang , Alistair Popple , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Neha Gholkar , kvm@vger.kernel.org, rick.p.edgecombe@intel.com, vishal.l.verma@intel.com Subject: Re: [PATCH] mm: mempolicy: fix automatic numa balancing for shmem Message-ID: References: <20260629163337.1264881-1-hannes@cmpxchg.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Thu, Jul 23, 2026 at 03:30:52PM -0700, Yosry Ahmed wrote: > On Thu, Jul 23, 2026 at 11:45 AM Gregory Price wrote: > > > > Walking this all back: > > > > - MPOL_DEFAULT is the default policy > > - numa_balancing=on means enable NUMA_BALANCING on the defaul policy > > - shmem was broken and did not respect this > > > > Johannes' fix is correct, and there are no additional changes required. > > > > Users enabling numa balancing while running KVM with shared regions are > > not getting what they're asking for presently - that is a bug. > > > > They should get the performance hit they're asking for (and then either > > turn off numa balancing or set an explicit mempolicy for those tasks / > > memfd's). > > Does it make sense to add a pr_warn() or pr_info() to help users > figure this out when they see a regression? I'm not sure in what scenario we would do this that doesn't simple reduce to "You turned numa balancing on". Not against it. ~Gregory