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a=rsa-sha256; c=relaxed/relaxed; d=stgolabs.net; s=dreamhost; t=1742507462; bh=rKnRuj1sOu1P6GoDMqyMdLAxFo1dk1B7Wxfi2jiBslQ=; h=Date:From:To:Cc:Subject:Content-Type; b=Zirxau5Gg+fixQD8oJaOo/EhgqYA95gOT5zQ0Lt8ulojHb2y04BLjtm5yOHukUXwO CFe9jLHE51bHO4x7xpV+pGADEXUmi+NQfMke0uotwCrLHADSwNrf+X3JHTeWfVR8/Z zaFjp5z4wG2c70vA3Gpvv9h4vjmPgHFX0nsuaPF3KLfym9TmGA4VeWvlN8s34cGFdQ LqV3plDIdVhUmOrycylqHMpzo3kLdTRbRApaxS3W8ZkyGk5DIDfL9L7DmVIgC3HxcL oLJW5cNIRjrjO1zatLFeJlVkkxgGrDlchLTJ0fK99CCw1kHyPznXVmSN3v/XaAUtpK KNH28qH5wLh9A== Date: Thu, 20 Mar 2025 14:50:56 -0700 From: Davidlohr Bueso To: Raghavendra K T Cc: AneeshKumar.KizhakeVeetil@arm.com, Hasan.Maruf@amd.com, Michael.Day@amd.com, akpm@linux-foundation.org, bharata@amd.com, dave.hansen@intel.com, david@redhat.com, dongjoo.linux.dev@gmail.com, feng.tang@intel.com, gourry@gourry.net, hannes@cmpxchg.org, honggyu.kim@sk.com, hughd@google.com, jhubbard@nvidia.com, jon.grimm@amd.com, k.shutemov@gmail.com, kbusch@meta.com, kmanaouil.dev@gmail.com, leesuyeon0506@gmail.com, leillc@google.com, liam.howlett@oracle.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, mgorman@techsingularity.net, mingo@redhat.com, nadav.amit@gmail.com, nphamcs@gmail.com, peterz@infradead.org, riel@surriel.com, rientjes@google.com, rppt@kernel.org, santosh.shukla@amd.com, shivankg@amd.com, shy828301@gmail.com, sj@kernel.org, vbabka@suse.cz, weixugc@google.com, willy@infradead.org, ying.huang@linux.alibaba.com, ziy@nvidia.com, Jonathan.Cameron@huawei.com, alok.rathore@samsung.com Subject: Re: [RFC PATCH V1 00/13] mm: slowtier page promotion based on PTE A bit Message-ID: <20250320215056.miwm2vdphdksrfjx@offworld> Mail-Followup-To: Raghavendra K T , AneeshKumar.KizhakeVeetil@arm.com, Hasan.Maruf@amd.com, Michael.Day@amd.com, akpm@linux-foundation.org, bharata@amd.com, dave.hansen@intel.com, david@redhat.com, dongjoo.linux.dev@gmail.com, feng.tang@intel.com, gourry@gourry.net, hannes@cmpxchg.org, honggyu.kim@sk.com, hughd@google.com, jhubbard@nvidia.com, jon.grimm@amd.com, k.shutemov@gmail.com, kbusch@meta.com, kmanaouil.dev@gmail.com, leesuyeon0506@gmail.com, leillc@google.com, liam.howlett@oracle.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, mgorman@techsingularity.net, mingo@redhat.com, nadav.amit@gmail.com, nphamcs@gmail.com, peterz@infradead.org, riel@surriel.com, rientjes@google.com, rppt@kernel.org, santosh.shukla@amd.com, shivankg@amd.com, shy828301@gmail.com, sj@kernel.org, vbabka@suse.cz, weixugc@google.com, willy@infradead.org, ying.huang@linux.alibaba.com, ziy@nvidia.com, Jonathan.Cameron@huawei.com, alok.rathore@samsung.com References: <20250319193028.29514-1-raghavendra.kt@amd.com> <20250319230015.bewglxf3hrf2mx3f@offworld> <52b2c1dd-2f4a-42fa-8a40-bd3664e7c56a@amd.com> 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=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: <52b2c1dd-2f4a-42fa-8a40-bd3664e7c56a@amd.com> User-Agent: NeoMutt/20220429 On Thu, 20 Mar 2025, Raghavendra K T wrote: >>Does NUMAB2 continue to exist? Are there any benefits in having two >>sources? >> > >I think there is surely a benefit in having two sources. I think I was a bit vague. What I'm really asking is if the scanning is done async (kmmscand), should NUMAB2 also exist as a source and also feed into the migrator? Looking at it differently, I guess doing so would allow additional flexibility in choosing what to use. >NUMAB2 is more accurate but slow learning. Yes. Which is also why it is important to have demotion in the picture to measure the ping pong effect. LRU based heuristics work best here. >IBS: No scan overhead but we need more sampledata. >PTE A bit: more scanning overhead (but was not much significant to >impact performance when compared with NUMAB1/NUMAB2, rather it was more >performing because of proactive migration) but has less accurate data on >hotness, target_node(?). > >When system is more stable, IBS was more effective. IBS will never be as effective as it should be simply because of the lack of time decay/frequency (hence all that related phi hackery in the kpromoted series). It has a global view of memory, it should beat any sw scanning heuristics by far but the numbers have lacked. As you know, PeterZ, Dave Hansen, Ying and I have expressed concerns about this in the past. But that is not to say it does not serve as a source, as you point out. Thanks, Davidlohr