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b=gIVenmFHF231TQyCG+S1zN/DVz5Qv5vX0FXXoppNS4GbF2zCh8za2hYE7PtBg3p7n zTaOWiLDpm4N/FOhfci1iJmw6yT1Uk35vaKfhcGHQNa5WQkCP2DrbVqVtMc/8V3V/A hVCU9Qk9Sd7AHapaz5WD9osrVraJ3ABpnFgii4PmuG72z8zL0ayPbXNINB1loDxlLH ZFV4sEYKodCdeUbcql1tp+xfp15veo0jf4/gYf64xTrIiG0AfhYZ2llALVmJkneV6s 1QappZXXU915bmvYx1Di/vz1QTu6zUFZn34GCBKikV6Wx7Ksyle+9C+KkOibhXe4nM XB1w1508ztSmQ== Date: Wed, 8 Apr 2026 12:52:26 +0900 From: "Harry Yoo (Oracle)" To: Joshua Hahn Cc: Johannes Weiner , Andrew Morton , Michal Hocko , Yosry Ahmed , Roman Gushchin , Shakeel Butt , Muchun Song , David Hildenbrand , Lorenzo Stoakes , Vlastimil Babka , Dennis Zhou , Tejun Heo , Christoph Lameter , cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@meta.com Subject: Re: [PATCH v2] mm/percpu, memcontrol: Per-memcg-lruvec percpu accounting Message-ID: References: <20260408034025.3317937-1-joshua.hahnjy@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260408034025.3317937-1-joshua.hahnjy@gmail.com> X-Rspam-User: X-Rspamd-Queue-Id: 19B6840007 X-Stat-Signature: ya9b4etdytzx53et45omn8xcab8thdrn X-Rspamd-Server: rspam06 X-HE-Tag: 1775620349-240912 X-HE-Meta: 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 +vXwrV0N T3CCSiNMW3LKES2jBcpTRT+hpd4fmYclKygUDiNb1rUjpa3e1UnWzsGDcPryYhMeXzQ078yr6oMsnPhJeIX0vBzhZeolJf2pWUrzMtsvo1dQi0PpjRQ3nxTsCuXyt7myrW4kGT2UrbYShQj+gqpZ4XRY05CggA4qA0XhElg5DH0FTRQqvJSbWhoqikXVOfoedBFaQlKJztLuyJVGl3jTTd384+08olSk2iP8bFea+afU8aJwbZEoiaiubqOan+yr4ecZ4NUiOeZBXqUSjJKJshCOlXNP+tFxVVN11e9RpM1DyxjZRMUB5QVf7HqwQCMjp7fMenJ0migNbGY/gLlJNPJJnMtHwhI2N5IJf Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Apr 07, 2026 at 08:40:24PM -0700, Joshua Hahn wrote: > On Wed, 8 Apr 2026 11:40:27 +0900 "Harry Yoo (Oracle)" wrote: > > On Fri, Apr 03, 2026 at 08:38:43PM -0700, Joshua Hahn wrote: > > > diff --git a/mm/percpu-vm.c b/mm/percpu-vm.c > > > index 4f5937090590d..e36b639f521dd 100644 > > > --- a/mm/percpu-vm.c > > > +++ b/mm/percpu-vm.c > > > @@ -65,6 +66,10 @@ static void pcpu_free_pages(struct pcpu_chunk *chunk, > > > __free_page(page); > > > } > > > } > > > + > > > + for_each_node(nid) > > > + mod_node_page_state(NODE_DATA(nid), NR_PERCPU_B, > > > + -1L * nr_pages * nr_cpus_node(nid) * PAGE_SIZE); > > > > Can this end up with mis-accounting due to CPU hotplug? > > Hey Harry, thanks for giving this patch a look! np :) > Yes, definitely. I think the solution is just to charge based on possible > CPUs, even if that might lead to some inaccuracy (by however many CPUs > aren't online at that moment). Yeah, that sounds fine to me. Not sure if there's nr_cpus_node() equivalent for possible CPUs though. > Seems like that's what already happens > in memcg anyways, so I think this discrepancy is OK to tolerate. Agreed. > Will spin up a v3! Thanks a lot, Harry! Have a great day : -) You too! -- Cheers, Harry / Hyeonggon