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01 Sep 2022 22:15:17 -0700 X-IronPort-AV: E=Sophos;i="5.93,283,1654585200"; d="scan'208";a="941152563" Received: from yhuang6-desk2.sh.intel.com (HELO yhuang6-desk2.ccr.corp.intel.com) ([10.238.208.55]) by fmsmga005-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 01 Sep 2022 22:15:13 -0700 From: "Huang, Ying" To: Wei Xu Cc: Aneesh Kumar K V , 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 Subject: Re: [PATCH v3 updated] mm/demotion: Expose memory tier details via sysfs In-Reply-To: (Wei Xu's message of "Thu, 1 Sep 2022 22:09:13 -0700") 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> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.1 (gnu/linux) Date: Fri, 02 Sep 2022 13:15:04 +0800 Message-ID: <87k06mz7af.fsf@yhuang6-desk2.ccr.corp.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1662095719; a=rsa-sha256; cv=none; b=nI2gf2Def8He0mpS6nQYQpLrABHTRqdGPyNZZn41QsIkWQ0d5XE3DAekhrl6Y63dNATFoq p0jHErKPUWlvlmmzYyIhw/buOysvOjNNt6DlefRyANWsBwquqNLETxxzHVV5/B92l3khcV 2B9xJA/5QAMHHwodaw1qZnfsD0NIrHQ= ARC-Authentication-Results: i=1; imf17.hostedemail.com; dkim=none ("invalid DKIM record") header.d=intel.com header.s=Intel header.b=LacVxnDH; spf=pass (imf17.hostedemail.com: domain of ying.huang@intel.com designates 192.55.52.115 as permitted sender) smtp.mailfrom=ying.huang@intel.com; dmarc=pass (policy=none) header.from=intel.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1662095719; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=VRi5a1sxCa97O+bWotGLB/c+asMr1FexBw4BqNKA6pc=; b=spQUJkm1rc1WOrNWexO3pmrbDMavZl6BDRqtiITQgTaMIL8+evqWhisbgXj90QfaLK5pJO oZcNYrLY288lu07fM2JZdHZiYbrCAlRRaO/EX6hhQgDj+8wD3vT8/zr2GwLDf7+9SkoYqq zghAFK/+9Zj3XRQkTVJAvn0AmIzWX6E= X-Stat-Signature: xcydcuoach8g9j5yf5k81p1nn5s1diqn X-Rspam-User: X-Rspamd-Queue-Id: 63D1640048 X-Rspamd-Server: rspam07 Authentication-Results: imf17.hostedemail.com; dkim=none ("invalid DKIM record") header.d=intel.com header.s=Intel header.b=LacVxnDH; spf=pass (imf17.hostedemail.com: domain of ying.huang@intel.com designates 192.55.52.115 as permitted sender) smtp.mailfrom=ying.huang@intel.com; dmarc=pass (policy=none) header.from=intel.com X-HE-Tag: 1662095718-125942 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: Wei Xu writes: > 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 memor= y tier >> >>> related details can be found. All allocated memory tiers will be lis= ted >> >>> 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. >> >> >> >>> >> >>> A directory hierarchy looks like >> >>> :/sys/devices/virtual/memory_tiering$ tree memory_tier4/ >> >>> memory_tier4/ >> >>> =E2=94=9C=E2=94=80=E2=94=80 nodes >> >>> =E2=94=9C=E2=94=80=E2=94=80 subsystem -> ../../../../bus/memory_tier= ing >> >>> =E2=94=94=E2=94=80=E2=94=80 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 u= ser >> >> 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. Yes. It's possible for us to change this in the future. > 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. Thanks! Best Regards, Huang, Ying >> >> Do we need a way to show the default memory tier in sysfs? That is, = the >> >> memory tier that the DRAM nodes belong to. >> >> >> > >> > I will hold adding that until we have support for modifying memory tie= r details from >> > userspace. That is when userspace would want to know about the default= memory tier. >> > >> > For now, the user interface is a simpler hierarchy of memory tiers, it= 's associated >> > nodes and the list of nodes from which promotion is not done. >> >> OK. >> >> Best Regards, >> Huang, Ying