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[173.79.56.208]) by smtp.gmail.com with ESMTPSA id d75a77b69052e-471f0eba93dsm24748191cf.80.2025.02.18.09.03.18 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 18 Feb 2025 09:03:19 -0800 (PST) Date: Tue, 18 Feb 2025 12:03:17 -0500 From: Gregory Price To: David Hildenbrand Cc: lsf-pc@lists.linux-foundation.org, linux-mm@kvack.org, linux-cxl@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: CXL Boot to Bash - Section 3: Memory (block) Hotplug Message-ID: References: <2f759351-a01f-4b1a-bf37-793a42a67c69@redhat.com> Precedence: bulk X-Mailing-List: linux-cxl@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2f759351-a01f-4b1a-bf37-793a42a67c69@redhat.com> On Tue, Feb 18, 2025 at 05:24:30PM +0100, David Hildenbrand wrote: > > > > ZONE_MOVABLE, under normal conditions, disallows most kernel allocations. > > > > In essence, only movable allocations (some kernel allcoations are movable). > > > ZONE_MOVABLE does NOT make a *strong* guarantee of hut-unplug-ability. > > The kernel and privileged users can cause long-term pinning to occur - > > even in ZONE_MOVABLE. It should be seen as a best-attempt at providing > > hot-unplug-ability under normal conditions. > > Yes and no; actual long-term pinning is disallowed (FOLL_LONGTERM), but we > have a bunch of cases that need fixing. [1] > > Of course, new cases keep popping up. It's a constant fight to make > hot-unplug as reliable as possible. So yes, we cannot give "strong" > guarantees, but make it as reliable as possible in sane configurations. > > [1] > https://lkml.kernel.org/r/882b566c-34d6-4e68-9447-6c74a0693f18@redhat.com > Appreciate the additional context, I missed your topic proposal. I was trying to be conservative about the claims ZONE_MOVABLE makes so that I don't present it as a "This will fix all your hotplug woes" solution. Looking forward to this LSF :] ~Gregory