From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 83FD6C433FE for ; Thu, 21 Apr 2022 05:41:26 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 042A76B0071; Thu, 21 Apr 2022 01:41:26 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id F0D746B0073; Thu, 21 Apr 2022 01:41:25 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id DAE016B0074; Thu, 21 Apr 2022 01:41:25 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (relay.hostedemail.com [64.99.140.27]) by kanga.kvack.org (Postfix) with ESMTP id C53BA6B0071 for ; Thu, 21 Apr 2022 01:41:25 -0400 (EDT) Received: from smtpin13.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay10.hostedemail.com (Postfix) with ESMTP id 852BF11AC for ; Thu, 21 Apr 2022 05:41:25 +0000 (UTC) X-FDA: 79379788530.13.47365E4 Received: from mail-ua1-f45.google.com (mail-ua1-f45.google.com [209.85.222.45]) by imf12.hostedemail.com (Postfix) with ESMTP id 14E3E40015 for ; Thu, 21 Apr 2022 05:41:21 +0000 (UTC) Received: by mail-ua1-f45.google.com with SMTP id z15so1421414uad.7 for ; Wed, 20 Apr 2022 22:41:24 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=UmThAYEYivgdwp2Y4vIa0rs/3WUEoOgz2c6GWGEeEYs=; b=mxxQ8j+tAbN/MZaYJhis9U4lQT0GJ5t+sKgp86dl/89Bz532XTlCrm7DmckAypK1sL 1B9ujG5fVQXS8a0/VKHQ/89kIV1EzS5Ce/O8GVNb+CFR+9Nw+iIbKB2S32JkEn3FyFrJ 3feiwR2tZaPYywb/3N+QE2nFPE0JsAi2IRmCzKZqaprVQmSYDFQgRk1vQ8m6/IVDJ1sK Ml8i1d2pUOkifGyW4Wwty5Dbd3k+vpzrOTxk7lN+Yy9SGCndUqWV/Qf7wWA04DnH7KTs 7txauOo9EKdDi5zUK7QjcXg8zNJCqRmKk1w0KW/JuPC2wuLfssJpqRsGp+AhYpq5wDEq ynUA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=UmThAYEYivgdwp2Y4vIa0rs/3WUEoOgz2c6GWGEeEYs=; b=5mYdsAwBz2EBkBC4cATmlFQE+aWLKaErl1nxG32Hgt6NHLNw0hJsj5BZ3SVWYpR8RJ PsqXR4YghbqxbbUCWj+bp7y9kWOUb7t077pIgCKCCpX3mSKyf5SoD3RXYnJBudau15LH Uq2TLfYfvA30HLzvUIl1Zoto0F2LdpWL6lFT3ZcNEK+bPK/rIqdvhcsujX20KsZfuoRP 81osIYg7lTfU4pNC35h3px9ZpscsLRSTQIQIRfqEcx7cYwDHqKe/fCC0n650+QsTjFhe y4jZxH8GTD8XWl7Bp03Hlq7CfP9kM2oMXheTOiT57tCse1l89Qph3ToLCqQA4YxTcw9w xfRQ== X-Gm-Message-State: AOAM530Y4euoUFt+XYgn2B3RtUviF7uP7S3n0Ra2OlkUiTXcPqGpHi49 eA4xmmeRN2KMnMWI0mgprt512eTvuKyA+VHW0nOLdA== X-Google-Smtp-Source: ABdhPJxEZUsT+ouvZ1sWpwuNn9WrVFzpBFkyYi+xuSv9JHBXoJU99/G8Iafsa8jVMhG9J6JoVJClTC0vHphcip+YMHU= X-Received: by 2002:ab0:72c4:0:b0:360:2eb9:8711 with SMTP id g4-20020ab072c4000000b003602eb98711mr828650uap.4.1650519684266; Wed, 20 Apr 2022 22:41:24 -0700 (PDT) MIME-Version: 1.0 References: <20220413092206.73974-1-jvgediya@linux.ibm.com> <6365983a8fbd8c325bb18959c51e9417fd821c91.camel@intel.com> In-Reply-To: From: Wei Xu Date: Wed, 20 Apr 2022 22:41:13 -0700 Message-ID: Subject: Re: [PATCH v2 0/5] mm: demotion: Introduce new node state N_DEMOTION_TARGETS To: Yang Shi Cc: "ying.huang@intel.com" , Jagdish Gediya , Linux MM , Linux Kernel Mailing List , Andrew Morton , "Aneesh Kumar K.V" , Baolin Wang , Dave Hansen , Dan Williams , Greg Thelen Content-Type: text/plain; charset="UTF-8" X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 14E3E40015 X-Stat-Signature: w8rgr1ggiino49ttkk6nhr535pm7xwco Authentication-Results: imf12.hostedemail.com; dkim=pass header.d=google.com header.s=20210112 header.b=mxxQ8j+t; spf=pass (imf12.hostedemail.com: domain of weixugc@google.com designates 209.85.222.45 as permitted sender) smtp.mailfrom=weixugc@google.com; dmarc=pass (policy=reject) header.from=google.com X-Rspam-User: X-HE-Tag: 1650519681-98713 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: On Wed, Apr 20, 2022 at 8:12 PM Yang Shi wrote: > > On Thu, Apr 14, 2022 at 12:00 AM ying.huang@intel.com > wrote: > > > > On Wed, 2022-04-13 at 14:52 +0530, Jagdish Gediya wrote: > > > Current implementation to find the demotion targets works > > > based on node state N_MEMORY, however some systems may have > > > dram only memory numa node which are N_MEMORY but not the > > > right choices as demotion targets. > > > > > > This patch series introduces the new node state > > > N_DEMOTION_TARGETS, which is used to distinguish the nodes which > > > can be used as demotion targets, node_states[N_DEMOTION_TARGETS] > > > is used to hold the list of nodes which can be used as demotion > > > targets, support is also added to set the demotion target > > > list from user space so that default behavior can be overridden. > > > > It appears that your proposed user space interface cannot solve all > > problems. For example, for system as follows, > > > > Node 0 & 2 are cpu + dram nodes and node 1 are slow memory node near > > node 0, > > > > available: 3 nodes (0-2) > > node 0 cpus: 0 1 > > node 0 size: n MB > > node 0 free: n MB > > node 1 cpus: > > node 1 size: n MB > > node 1 free: n MB > > node 2 cpus: 2 3 > > node 2 size: n MB > > node 2 free: n MB > > node distances: > > node 0 1 2 > > 0: 10 40 20 > > 1: 40 10 80 > > 2: 20 80 10 > > > > Demotion order 1: > > > > node demotion_target > > 0 1 > > 1 X > > 2 X > > > > Demotion order 2: > > > > node demotion_target > > 0 1 > > 1 X > > 2 1 > > > > The demotion order 1 is preferred if we want to reduce cross-socket > > traffic. While the demotion order 2 is preferred if we want to take > > full advantage of the slow memory node. We can take any choice as > > automatic-generated order, while make the other choice possible via user > > space overridden. > > > > I don't know how to implement this via your proposed user space > > interface. How about the following user space interface? > > > > 1. Add a file "demotion_order_override" in > > /sys/devices/system/node/ > > > > 2. When read, "1" is output if the demotion order of the system has been > > overridden; "0" is output if not. > > > > 3. When write "1", the demotion order of the system will become the > > overridden mode. When write "0", the demotion order of the system will > > become the automatic mode and the demotion order will be re-generated. > > > > 4. Add a file "demotion_targets" for each node in > > /sys/devices/system/node/nodeX/ > > > > 5. When read, the demotion targets of nodeX will be output. > > > > 6. When write a node list to the file, the demotion targets of nodeX > > will be set to the written nodes. And the demotion order of the system > > will become the overridden mode. > > TBH I don't think having override demotion targets in userspace is > quite useful in real life for now (it might become useful in the > future, I can't tell). Imagine you manage hundred thousands of > machines, which may come from different vendors, have different > generations of hardware, have different versions of firmware, it would > be a nightmare for the users to configure the demotion targets > properly. So it would be great to have the kernel properly configure > it *without* intervening from the users. > > So we should pick up a proper default policy and stick with that > policy unless it doesn't work well for the most workloads. I do > understand it is hard to make everyone happy. My proposal is having > every node in the fast tier has a demotion target (at least one) if > the slow tier exists sounds like a reasonable default policy. I think > this is also the current implementation. > This is reasonable. I agree that with a decent default policy, the overriding of per-node demotion targets can be deferred. The most important problem here is that we should allow the configurations where memory-only nodes are not used as demotion targets, which this patch set has already addressed. > > > > To reduce the complexity, the demotion order of the system is either in > > overridden mode or automatic mode. When converting from the automatic > > mode to the overridden mode, the existing demotion targets of all nodes > > will be retained before being changed. When converting from overridden > > mode to automatic mode, the demotion order of the system will be re- > > generated automatically. > > > > In overridden mode, the demotion targets of the hot-added and hot- > > removed node will be set to empty. And the hot-removed node will be > > removed from the demotion targets of any node. > > > > This is an extention of the interface used in the following patch, > > > > https://lore.kernel.org/lkml/20191016221149.74AE222C@viggo.jf.intel.com/ > > > > What do you think about this? > > > > > node state N_DEMOTION_TARGETS is also set from the dax kmem > > > driver, certain type of memory which registers through dax kmem > > > (e.g. HBM) may not be the right choices for demotion so in future > > > they should be distinguished based on certain attributes and dax > > > kmem driver should avoid setting them as N_DEMOTION_TARGETS, > > > however current implementation also doesn't distinguish any > > > such memory and it considers all N_MEMORY as demotion targets > > > so this patch series doesn't modify the current behavior. > > > > > > > Best Regards, > > Huang, Ying > > > > [snip] > >