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[2003:cb:c709:a00:7d7d:3665:5fe4:7127]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-43961e07252sm39337615e9.14.2025.02.14.02.37.43 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 14 Feb 2025 02:37:45 -0800 (PST) Message-ID: <1404d6a3-c27d-4d51-8e3a-e10dc040dc6e@redhat.com> Date: Fri, 14 Feb 2025 11:37:42 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 00/17] mm: fixes for device-exclusive entries (hmm) To: Alistair Popple Cc: linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-mm@kvack.org, nouveau@lists.freedesktop.org, linux-trace-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org, damon@lists.linux.dev, Andrew Morton , =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= , Jonathan Corbet , Alex Shi , Yanteng Si , Karol Herbst , Lyude Paul , Danilo Krummrich , David Airlie , Simona Vetter , Masami Hiramatsu , Oleg Nesterov , Peter Zijlstra , SeongJae Park , "Liam R. Howlett" , Lorenzo Stoakes , Vlastimil Babka , Jann Horn , Pasha Tatashin , Peter Xu , Jason Gunthorpe References: <20250210193801.781278-1-david@redhat.com> <6sejv2hauce3il5lq6sw53xmjjjglxkhz5copm62oryga6jioi@u66wl2nc3hoy> <039b2e48-1d7c-48dc-b832-24db12af216a@redhat.com> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZgEEwEIAEICGwMGCwkIBwMCBhUIAgkKCwQW AgMBAh4BAheAAhkBFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl8Ox4kFCRKpKXgACgkQTd4Q 9wD/g1oHcA//a6Tj7SBNjFNM1iNhWUo1lxAja0lpSodSnB2g4FCZ4R61SBR4l/psBL73xktp rDHrx4aSpwkRP6Epu6mLvhlfjmkRG4OynJ5HG1gfv7RJJfnUdUM1z5kdS8JBrOhMJS2c/gPf wv1TGRq2XdMPnfY2o0CxRqpcLkx4vBODvJGl2mQyJF/gPepdDfcT8/PY9BJ7FL6Hrq1gnAo4 3Iv9qV0JiT2wmZciNyYQhmA1V6dyTRiQ4YAc31zOo2IM+xisPzeSHgw3ONY/XhYvfZ9r7W1l pNQdc2G+o4Di9NPFHQQhDw3YTRR1opJaTlRDzxYxzU6ZnUUBghxt9cwUWTpfCktkMZiPSDGd KgQBjnweV2jw9UOTxjb4LXqDjmSNkjDdQUOU69jGMUXgihvo4zhYcMX8F5gWdRtMR7DzW/YE BgVcyxNkMIXoY1aYj6npHYiNQesQlqjU6azjbH70/SXKM5tNRplgW8TNprMDuntdvV9wNkFs 9TyM02V5aWxFfI42+aivc4KEw69SE9KXwC7FSf5wXzuTot97N9Phj/Z3+jx443jo2NR34XgF 89cct7wJMjOF7bBefo0fPPZQuIma0Zym71cP61OP/i11ahNye6HGKfxGCOcs5wW9kRQEk8P9 M/k2wt3mt/fCQnuP/mWutNPt95w9wSsUyATLmtNrwccz63XOwU0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAHCwXwEGAEIACYCGwwWIQQb2cqtc1xMOkYN/MpN3hD3 AP+DWgUCXw7HsgUJEqkpoQAKCRBN3hD3AP+DWrrpD/4qS3dyVRxDcDHIlmguXjC1Q5tZTwNB boaBTPHSy/Nksu0eY7x6HfQJ3xajVH32Ms6t1trDQmPx2iP5+7iDsb7OKAb5eOS8h+BEBDeq 3ecsQDv0fFJOA9ag5O3LLNk+3x3q7e0uo06XMaY7UHS341ozXUUI7wC7iKfoUTv03iO9El5f XpNMx/YrIMduZ2+nd9Di7o5+KIwlb2mAB9sTNHdMrXesX8eBL6T9b+MZJk+mZuPxKNVfEQMQ a5SxUEADIPQTPNvBewdeI80yeOCrN+Zzwy/Mrx9EPeu59Y5vSJOx/z6OUImD/GhX7Xvkt3kq Er5KTrJz3++B6SH9pum9PuoE/k+nntJkNMmQpR4MCBaV/J9gIOPGodDKnjdng+mXliF3Ptu6 3oxc2RCyGzTlxyMwuc2U5Q7KtUNTdDe8T0uE+9b8BLMVQDDfJjqY0VVqSUwImzTDLX9S4g/8 kC4HRcclk8hpyhY2jKGluZO0awwTIMgVEzmTyBphDg/Gx7dZU1Xf8HFuE+UZ5UDHDTnwgv7E th6RC9+WrhDNspZ9fJjKWRbveQgUFCpe1sa77LAw+XFrKmBHXp9ZVIe90RMe2tRL06BGiRZr jPrnvUsUUsjRoRNJjKKA/REq+sAnhkNPPZ/NNMjaZ5b8Tovi8C0tmxiCHaQYqj7G2rgnT0kt WNyWQQ== Organization: Red Hat In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 14.02.25 02:25, Alistair Popple wrote: > On Thu, Feb 13, 2025 at 12:15:58PM +0100, David Hildenbrand wrote: >> On 13.02.25 12:03, Alistair Popple wrote: >>> On Mon, Feb 10, 2025 at 08:37:42PM +0100, David Hildenbrand wrote: >>>> Against mm-hotfixes-stable for now. >>>> >>>> Discussing the PageTail() call in make_device_exclusive_range() with >>>> Willy, I recently discovered [1] that device-exclusive handling does >>>> not properly work with THP, making the hmm-tests selftests fail if THPs >>>> are enabled on the system. >>>> >>>> Looking into more details, I found that hugetlb is not properly fenced, >>>> and I realized that something that was bugging me for longer -- how >>>> device-exclusive entries interact with mapcounts -- completely breaks >>>> migration/swapout/split/hwpoison handling of these folios while they have >>>> device-exclusive PTEs. >>>> >>>> The program below can be used to allocate 1 GiB worth of pages and >>>> making them device-exclusive on a kernel with CONFIG_TEST_HMM. >>>> >>>> Once they are device-exclusive, these folios cannot get swapped out >>>> (proc$pid/smaps_rollup will always indicate 1 GiB RSS no matter how >>>> much one forces memory reclaim), and when having a memory block onlined >>>> to ZONE_MOVABLE, trying to offline it will loop forever and complain about >>>> failed migration of a page that should be movable. >>>> >>>> # echo offline > /sys/devices/system/memory/memory136/state >>>> # echo online_movable > /sys/devices/system/memory/memory136/state >>>> # ./hmm-swap & >>>> ... wait until everything is device-exclusive >>>> # echo offline > /sys/devices/system/memory/memory136/state >>>> [ 285.193431][T14882] page: refcount:2 mapcount:0 mapping:0000000000000000 >>>> index:0x7f20671f7 pfn:0x442b6a >>>> [ 285.196618][T14882] memcg:ffff888179298000 >>>> [ 285.198085][T14882] anon flags: 0x5fff0000002091c(referenced|uptodate| >>>> dirty|active|owner_2|swapbacked|node=1|zone=3|lastcpupid=0x7ff) >>>> [ 285.201734][T14882] raw: ... >>>> [ 285.204464][T14882] raw: ... >>>> [ 285.207196][T14882] page dumped because: migration failure >>>> [ 285.209072][T14882] page_owner tracks the page as allocated >>>> [ 285.210915][T14882] page last allocated via order 0, migratetype >>>> Movable, gfp_mask 0x140dca(GFP_HIGHUSER_MOVABLE|__GFP_COMP|__GFP_ZERO), >>>> id 14926, tgid 14926 (hmm-swap), ts 254506295376, free_ts 227402023774 >>>> [ 285.216765][T14882] post_alloc_hook+0x197/0x1b0 >>>> [ 285.218874][T14882] get_page_from_freelist+0x76e/0x3280 >>>> [ 285.220864][T14882] __alloc_frozen_pages_noprof+0x38e/0x2740 >>>> [ 285.223302][T14882] alloc_pages_mpol+0x1fc/0x540 >>>> [ 285.225130][T14882] folio_alloc_mpol_noprof+0x36/0x340 >>>> [ 285.227222][T14882] vma_alloc_folio_noprof+0xee/0x1a0 >>>> [ 285.229074][T14882] __handle_mm_fault+0x2b38/0x56a0 >>>> [ 285.230822][T14882] handle_mm_fault+0x368/0x9f0 >>>> ... >>>> >>>> This series fixes all issues I found so far. There is no easy way to fix >>>> without a bigger rework/cleanup. I have a bunch of cleanups on top (some >>>> previous sent, some the result of the discussion in v1) that I will send >>>> out separately once this landed and I get to it. >>>> I wish we could just use some special present PROT_NONE PTEs instead of > > Yeah, that was my initial instinct when I first investigated this. As you point > out a lack of spare PTE bits made it hard/impossible. Of course I'm about to > give you all one back, maybe I should keep it :) I'm only kidding though - I'm > sure there's more interesting things to spend it on. Yes. And I think it could actually be valuable to have the option for more fake-prot-none things. For example, right now we cannot really distinguish NUMA-hinting prot-none from ordinary prot-none without guessing based on some VMA flags. One could implement NUMA-hinting using a PFN swap entry in an arch-independent way I guess. So there are pros and cons to it. The biggest con is, that while RMAP can now handle it, other page table walkers mostly skip these entries. > >>> >>> First off David thanks for finding and fixing these issues. If you have further >>> clean-ups in mind that you need help with please let me know as I'd be happy >>> to help. >> >> Sure! I have some cleanups TBD as result of the previous discussion, but >> nothing bigger so far. >> >> (removing the folio lock could be considered bigger, if we want to go down >> that path) >> >>> >>>> these (non-present, non-none) fake-swap entries; but that just results in >>>> the same problem we keep having (lack of spare PTE bits), and staring at >>>> other similar fake-swap entries, that ship has sailed. >>>> >>>> With this series, make_device_exclusive() doesn't actually belong into >>>> mm/rmap.c anymore, but I'll leave moving that for another day. >>>> >>>> I only tested this series with the hmm-tests selftests due to lack of HW, >>>> so I'd appreciate some testing, especially if the interaction between >>>> two GPUs wanting a device-exclusive entry works as expected. >>> >>> I'm still reviewing the series but so far testing on my single GPU system >>> appears to be working as expected. I will try and fire up a dual GPU system >>> tomorrow and test it there as well. >> >> Great, thanks a bunch for testing! >> >> Out of interest: does the nvidia driver make use of this interface as well, >> and are you testing with that or with the nouveau driver? I saw some reports >> that nvidia at least checks for it [1] when building the module: > > Both. I have tested Nouveau with the Mesa OpenCL stack and a simple stress test > that just thrashes atomic accesses between CPU and GPU and a similar test for > the nvidia driver. > > In practice the nvidia driver probably doesn't use this that often as it > more aggressively migrates data but it does use this as a fallback. Also it's > possible for users to force residency on the CPU in which case this is used, > which is what the test does. Cool, thanks! (so even though nouveau is not enabled in RHEL, we'd effectively be using that functionality in RHEL kernels using the nvidia driver) > > Anyway I have just finished testing on a multi-GPU setup so please feel free to > add for the series: > > Tested-by: Alistair Popple Thanks a bunch! -- Cheers, David / dhildenb