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Fri, 2 Sep 2022 05:23:41 +0000 (GMT) Received: from [9.43.64.219] (unknown [9.43.64.219]) by d06av22.portsmouth.uk.ibm.com (Postfix) with ESMTP; Fri, 2 Sep 2022 05:23:41 +0000 (GMT) Message-ID: Date: Fri, 2 Sep 2022 10:53:40 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.2.0 Subject: Re: [PATCH v3 updated] mm/demotion: Expose memory tier details via sysfs Content-Language: en-US To: Wei Xu , "Huang, Ying" Cc: Johannes Weiner , Linux MM , Andrew Morton , Yang Shi , Davidlohr Bueso , Tim C Chen , Michal Hocko , Linux Kernel Mailing List , Hesham Almatary , Dave Hansen , Jonathan Cameron , Alistair Popple , Dan Williams , jvgediya.oss@gmail.com, Bharata B Rao , Greg Thelen References: <20220830081736.119281-1-aneesh.kumar@linux.ibm.com> <87tu5rzigc.fsf@yhuang6-desk2.ccr.corp.intel.com> <87pmgezkhp.fsf@yhuang6-desk2.ccr.corp.intel.com> From: Aneesh Kumar K V In-Reply-To: Content-Type: text/plain; charset=UTF-8 X-TM-AS-GCONF: 00 X-Proofpoint-GUID: JVbLPad--HYiCEG4zpi3nnsqOoocNTdu X-Proofpoint-ORIG-GUID: _QRjILfWhJm9MSUJf7nlcEmHJd8-cy2j Content-Transfer-Encoding: 8bit X-Proofpoint-UnRewURL: 0 URL was un-rewritten MIME-Version: 1.0 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.205,Aquarius:18.0.895,Hydra:6.0.517,FMLib:17.11.122.1 definitions=2022-09-01_12,2022-08-31_03,2022-06-22_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 bulkscore=0 adultscore=0 malwarescore=0 priorityscore=1501 mlxscore=0 clxscore=1015 mlxlogscore=993 impostorscore=0 spamscore=0 suspectscore=0 lowpriorityscore=0 phishscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2207270000 definitions=main-2209020021 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 9/2/22 10:39 AM, Wei Xu wrote: > On Thu, Sep 1, 2022 at 5:33 PM Huang, Ying wrote: >> >> Aneesh Kumar K V writes: >> >>> On 9/1/22 12:31 PM, Huang, Ying wrote: >>>> "Aneesh Kumar K.V" writes: >>>> >>>>> This patch adds /sys/devices/virtual/memory_tiering/ where all memory tier >>>>> related details can be found. All allocated memory tiers will be listed >>>>> there as /sys/devices/virtual/memory_tiering/memory_tierN/ >>>>> >>>>> The nodes which are part of a specific memory tier can be listed via >>>>> /sys/devices/virtual/memory_tiering/memory_tierN/nodes >>>> >>>> I think "memory_tier" is a better subsystem/bus name than >>>> memory_tiering. Because we have a set of memory_tierN devices inside. >>>> "memory_tier" sounds more natural. I know this is subjective, just my >>>> preference. >>>> I missed replying to this earlier. I will keep memory_tiering as subsystem name in v4 because we would want it to a susbsystem where all memory tiering related details can be found including memory type in the future. This is as per discussion https://lore.kernel.org/linux-mm/CAAPL-u9TKbHGztAF=r-io3gkX7gorUunS2UfstudCWuihrA=0g@mail.gmail.com >>>>> >>>>> A directory hierarchy looks like >>>>> :/sys/devices/virtual/memory_tiering$ tree memory_tier4/ >>>>> memory_tier4/ >>>>> ├── nodes >>>>> ├── subsystem -> ../../../../bus/memory_tiering >>>>> └── uevent >>>>> >>>>> All toptier nodes are listed via >>>>> /sys/devices/virtual/memory_tiering/toptier_nodes >>>>> >>>>> :/sys/devices/virtual/memory_tiering$ cat toptier_nodes >>>>> 0,2 >>>>> :/sys/devices/virtual/memory_tiering$ cat memory_tier4/nodes >>>>> 0,2 >>>> >>>> I don't think that it is a good idea to show toptier information in user >>>> space interface. Because it is just a in kernel implementation >>>> details. Now, we only promote pages from !toptier to toptier. But >>>> there may be multiple memory tiers in toptier and !toptier, we may >>>> change the implementation in the future. For example, we may promote >>>> pages from DRAM to HBM in the future. >>>> >>> >>> >>> In the case you describe above and others, we will always have a list of >>> NUMA nodes from which memory promotion is not done. >>> /sys/devices/virtual/memory_tiering/toptier_nodes shows that list. >> >> I don't think we will need that interface if we don't restrict promotion >> in the future. For example, he can just check the memory tier with >> smallest number. >> >> TBH, I don't know why do we need that interface. What is it for? We >> don't want to expose unnecessary information to restrict our in kernel >> implementation in the future. >> >> So, please remove that interface at least before we discussing it >> thoroughly. > > I have asked for this interface to allow the userspace to query a list > of top-tier nodes as the targets of userspace-driven promotions. The > idea is that demotion can gradually go down tier by tier, but we > promote hot pages directly to the top-tier and bypass the immediate > tiers. > > Certainly, this can be viewed as a policy choice. Given that now we > have a clearly defined memory tier hierarchy in sysfs and the > toptier_nodes content can be constructed from this memory tier > hierarchy and other information from the node sysfs interfaces, I am > fine if we want to remove toptier_nodes and keep the current memory > tier sysfs interfaces to the minimal. > Ok I can do a v4 with toptier_nodes dropped. -aneesh