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Mon, 6 Oct 2025 10:53:48 +0100 Date: Mon, 6 Oct 2025 10:53:46 +0100 From: Jonathan Cameron To: Bharata B Rao CC: , , , , , , , , , , , , , , , , , , , , , , , , , , , Subject: Re: [RFC PATCH v2 8/8] mm: sched: Move hot page promotion from NUMAB=2 to kpromoted Message-ID: <20251006105346.00004634@huawei.com> In-Reply-To: References: <20250910144653.212066-1-bharata@amd.com> <20250910144653.212066-9-bharata@amd.com> <20251003133818.000017af@huawei.com> X-Mailer: Claws Mail 4.3.0 (GTK 3.24.42; x86_64-w64-mingw32) MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.203.177.15] X-ClientProxiedBy: lhrpeml100011.china.huawei.com (7.191.174.247) To dubpeml100005.china.huawei.com (7.214.146.113) X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 93A84C0004 X-Stat-Signature: x788dfch64xtk6dujuyuc3byrpp5giya X-HE-Tag: 1759744433-513476 X-HE-Meta: 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 TiQ== 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 Mon, 6 Oct 2025 11:27:21 +0530 Bharata B Rao wrote: > On 03-Oct-25 6:08 PM, Jonathan Cameron wrote: > > On Wed, 10 Sep 2025 20:16:53 +0530 > > Bharata B Rao wrote: > > > >> Currently hot page promotion (NUMA_BALANCING_MEMORY_TIERING > >> mode of NUMA Balancing) does hot page detection (via hint faults), > >> hot page classification and eventual promotion, all by itself and > >> sits within the scheduler. > >> > >> With the new hot page tracking and promotion mechanism being > >> available, NUMA Balancing can limit itself to detection of > >> hot pages (via hint faults) and off-load rest of the > >> functionality to the common hot page tracking system. > >> > >> pghot_record_access(PGHOT_HINT_FAULT) API is used to feed the > >> hot page info. In addition, the migration rate limiting and > >> dynamic threshold logic are moved to kpromoted so that the same > >> can be used for hot pages reported by other sources too. > >> > >> Signed-off-by: Bharata B Rao > > > > Making a direct replacement without any fallback to previous method > > is going to need a lot of data to show there are no important regressions. > > > > So bold move if that's the intent! > > Firstly I am only moving the existing hot page heuristics that is part of > NUMAB=2 to kpromoted so that the same can be applied to hot pages being > identified by other sources. So the hint fault mechanism that is inherent > to NUMAB=2 still remains. That makes sense. > > In fact, kscand effort started as a potential replacement for the existing > hot page promotion mechanism by getting rid of hint faults and moving the > page table scanning out of process context. Understood and I'm in favor of the that approach but not sure it will be a fit for all workloads. > > In any case, I will start including numbers from the next post. Great. > >> > >> static unsigned int sysctl_pghot_freq_window = KPROMOTED_FREQ_WINDOW; > >> > >> +/* Restrict the NUMA promotion throughput (MB/s) for each target node. */ > >> +static unsigned int sysctl_pghot_promote_rate_limit = 65536; > > > > If the comment correlates with the value, this is 64 GiB/s? That seems > > unlikely if I guess possible. > > IIUC, the existing logic tries to limit promotion rate to 64 GiB/s by > limiting the number of candidate pages that are promoted within the > 1s observation interval. > > Are you saying that achieving the rate of 64 GiB/s is not possible > or unlikely? Seem rather too high to me, but maybe I just have the wrong mental model of what we should be moving. > > > > >> + > >> #ifdef CONFIG_SYSCTL > >> static const struct ctl_table pghot_sysctls[] = { > >> { > >> @@ -44,8 +50,17 @@ static const struct ctl_table pghot_sysctls[] = { > >> .proc_handler = proc_dointvec_minmax, > >> .extra1 = SYSCTL_ZERO, > >> }, > >> + { > >> + .procname = "pghot_promote_rate_limit_MBps", > >> + .data = &sysctl_pghot_promote_rate_limit, > >> + .maxlen = sizeof(unsigned int), > >> + .mode = 0644, > >> + .proc_handler = proc_dointvec_minmax, > >> + .extra1 = SYSCTL_ZERO, > >> + }, > >> }; > >> #endif > >> + > > Put that in earlier patch to reduce noise here. > > This patch moves the hot page heuristics to kpromoted and hence this > related sysctl is also being moved in this patch. I just mean the blank line - not the block above. This is just a patch set tidying up comment. Jonathan