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a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1776091997; bh=SmlzEupAcTl8dpDl/4W91ji9DI1If1QZKHMeX0jJhQE=; h=Date:Subject:From:To:Cc:References:In-Reply-To:From; b=lyhdxi9+o47SLGVSzeL9CygkaHYOoek0pzdVy7BBu91dQX4084zZ82Wv/hwCilFgh MGOPAIAfVk6v9hiIYj9WGra1wNEygiJb8BF34YYdTYlMXp8x8F8P5Zdxd0CDAsrgSm NQviKLgaFxwNCDEPdomHWocsjqctyl1FltdwYiiTYLPHYdzz8gnSL0UzOyrCPxyKdD jMyRjny+JBeV+/Wd9KzczDO8aEH+9qURUzJCBzjEiir8JtKDh0Gkq4j8itRc6EEOlb HwI9sucCsSOY7ISuTWPS4vCzlzeLbmhgBj8an1UbxrVXqvWEhW35mDm09diJl2asZC kaGLCumaCmRww== Message-ID: Date: Mon, 13 Apr 2026 16:53:10 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 0/8] dax/kmem: atomic whole-device hotplug via sysfs From: "David Hildenbrand (Arm)" 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> <4c08c0a8-9415-4f30-bfa9-db39318fa7d3@kernel.org> Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Stat-Signature: 83i8ja1gcahpttcifxtgfbokja1ouu3y X-Rspamd-Queue-Id: CCAA520011 X-Rspam-User: X-Rspamd-Server: rspam03 X-HE-Tag: 1776091998-840508 X-HE-Meta: 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 Y1H01ycx ceNMTzY0Tm/nqyWqNnUqxy7b3rETo9utTsTuzzJMmyEsWB0s8pLt0Fe0FJ1lBgc8jjVfJxZZhHqA1TObKqOoSkKxbDEaaS4Y0VFwiWE3xvrmLsBuDPoIi1n8cF2TcVp0M/PT1/OXwGSeDhAhUUDjhSQ2fLNNEObxTkrn4D74q0EY3Ic2Q2IYz7IVKxjkCLQe5RCT2Ev2byktrWbcqDhMy083/o6GQwnURlK4lqi458d6f03wbPaI5G1SXTmBMEK6wOOZc81qf8unLhqm0ELxW36MsttrsRr+ajqNFAQ8+O+/CIU4C+wDnbwno19vNT0FwXt5sM3SfiU7ozhIl4ZMwZX5Hn46WkKxYcSExs8POGP7zF97UMCbTGTvbNH3+pJM8d6gpbV8V/1X5YPLUnxAfxH9lR4kWYsv+mQ96culm7eHDu+M= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 4/13/26 16:49, David Hildenbrand (Arm) wrote: > 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? > b4 am --guess-base Was helpful :) -- Cheers, David