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a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1776091788; bh=mjWzHkibbJ+YGpg8iepNJ9fmO8lj/6ddY53/GhjosH0=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=HXyiDmP61caBFR6ZEDJhLV2kLFTrpfWmsebGSZkB4Sz+GvDVozGmf+j4Ma4qLWtHx vblYih3TDYo1K5L/hjqRnJSE/NNvB7I+g8EGy0zEZwP9FErtsWbxwx3MUUBbhwxjXR RiMs+KxEGJ72hftseV0cvzfNjc6QuH1kP9ywyULy3USoTE0IBt5Lkh/vHTRshbQBYO x0qd8ryPHY/QPw1CSAY7abXHysgOhE+zArf5GJu5t6o+6CYS8QeZudssfGWk8HRjTd NIgY1AhwDj7UyixFtsOC3h42MI8HKENmsWkIAwjZwEtCLjiNUUm87amLTdD59FHP6S 8PQtsyQyU1o7Q== Message-ID: <4c08c0a8-9415-4f30-bfa9-db39318fa7d3@kernel.org> Date: Mon, 13 Apr 2026 16:49:40 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 0/8] dax/kmem: atomic whole-device hotplug via sysfs To: Gregory Price , linux-mm@kvack.org, vishal.l.verma@intel.com, dave.jiang@intel.com, akpm@linux-foundation.org, osalvador@suse.de Cc: dan.j.williams@intel.com, ljs@kernel.org, Liam.Howlett@oracle.com, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, linux-kernel@vger.kernel.org, nvdimm@lists.linux.dev, linux-cxl@vger.kernel.org, kernel-team@meta.com References: <20260321150404.3288786-1-gourry@gourry.net> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: B6BEB8000C X-Stat-Signature: jw7gjji97opfseeps7axtyhkph6gkcd9 X-Rspam-User: X-Rspamd-Server: rspam04 X-HE-Tag: 1776091789-508000 X-HE-Meta: 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 HEdrYVK9 wkcbAl3Msr/A1/C82XzCeTP4OKXR+knvX4UxUScfRjt7aPSNo/PUwPT3KK7c1V0muRpcweU/jgw2vFWejfTHG7CTgB1mE5nSb1uauOtlsePQMuSBA446ix/UFmaMbyYoqWoc4eGWYhzMxnifLyYHwHFqpPi9v9wq9lZ3SsjGqA1SKLZxGUWwKvFZo/S1X13g0KoJe7CCQOV/teBDfxb5V7E3NBAT7I+N4JK3FrZ8VANoluRH2JdMGGuWNZpeUmOnvcJWw7HalJySUbEdhJ+f7krKKrFEBQqTAgi0Iyoc2c+iv/wMvWQsHDNrsuuyMYsGNH8xcHB/bfHDnWCC7PfPUaRvYLeO5zlI7Q7GZwAShyw67VB3l9MY1ZLobCjuk5DNC6QNP8uhXqirRrZl3ixh5SPG4Sx/bhc2WlQgsd2TcPBBs5FA= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 3/21/26 16:03, Gregory Price wrote: > The dax kmem driver currently onlines memory during probe using the > system default policy, with no way to control or query the region state > at runtime - other than by inspecting the state of individual blocks. > > Offlining and removing an entire region requires operating on individual > memory blocks, creating race conditions where external entities can > interfere between the offline and remove steps. > > The problem was discussed specifically in the LPC2025 device memory > sessions - https://lpc.events/event/19/contributions/2016/ - where > it was discussed how the non-atomic interface for dax hotplug is causing > issues in some distributions which have competing userland controllers > that interfere with each other. > > This series adds a sysfs "hotplug" attribute for atomic whole-device > hotplug control, along with the mm and dax plumbing to support it. > > The first five patches prepare the mm and dax layers: > > 1. Consolidate memory-tier type deduplication into mt_get_memory_type(), > removing redundant per-driver infrastructure. > 2. Add a memory_block_align_range() helper for hotplug range alignment. > 3-5. Thread an explicit online_type through the memory hotplug and dax > paths, allowing drivers to specify a preferred auto-online policy > (ZONE_NORMAL vs ZONE_MOVABLE) instead of being forced to the > system default. > > The last three patches build the dax/kmem feature: > > 6. Plumb online_type through the dax device creation path. > 7. Extract hotplug/hotremove into helper functions to separate resource > lifecycle from memory onlining. > 8. Add the "hotplug" sysfs attribute supporting three states: > - "unplug": memory blocks removed > - "online": online as normal system RAM > - "online_movable": online in ZONE_MOVABLE > > Transitions are atomic across all ranges in the device. Backward > compatibility is preserved: probe still auto-onlines when the configured > policy matches the system default. > > Specific notes for maintainers: > > I downgraded a BUG() to a WARN() when unbind is called while the dax > device is not un an UNPLUGGED state. This is because the old pattern of > toggling individual memory blocks is still used by userland tools, and > will disconnect the `hotplug` value from the actual state of the overall > memory region. > > Unless we move to deprecate per-block controls, we should just WARN() > instead of BUG() as an indicator that userland tools need to be updated > to use the new pattern (the old pattern is subject to race conditions). > > The first two commits are semi-unrelated cleanups that conflict with the > changes made in the refactoring commits. (memory-tier dedup and align_range > helper). These are intended to be used for future cxl region extensions, > but if you prefer them to be dropped or submitted separately let me > know. > > This is technically v3, but the patch line has diverged considerably and > I've reworked the cover letter, apologies for prior obtuseness > Link: https://lore.kernel.org/all/20260114235022.3437787-1-gourry@gourry.net/ Hi Gregory, against which branch / base commit is this series? -- Cheers, David