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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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2f759351-a01f-4b1a-bf37-793a42a67c69@redhat.com> X-Rspamd-Queue-Id: A6C2080006 X-Stat-Signature: aqnz1dkjmt3sezsidezstadkkgpjufw5 X-Rspam-User: X-Rspamd-Server: rspam10 X-HE-Tag: 1739898201-719120 X-HE-Meta: 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 fnQd4rst jtQFfMGbt00qUFOiTmA5M12yNj32HA1HNs/QjQwl0qwJ/auDqsh3SPmNQYdJlO8h89GyhGiOeEyeXU0LaiYxJREYMh34CBfVwUBB1JdgHAugiSOwkhdHgZcq0xwLwjK+NVMQOoLPpq0Y7hG7eaoYuKYhAarv/DMTgz6Wcq2nZVxaGGk1+MNoQb6rHgd7w0qlZs0Wn0NiOpJsv5fEwO7ePoM8aRM+Lt7JrfLK2ezcEX/WtSCxNCp64hl4e5oL9xClllEx5MWBhPQsyWi6y7KQ+tmYCv6jWcXzOaoGjyX8CljHWHnXgWQ6jD0gM4WBH2IC538ToB4kpIpNDjfETPDVbBvreFCCr4uXmiyViDhUWMCNBERUUhTiFJ/wE+g== 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: List-Subscribe: List-Unsubscribe: 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