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[84.136.37.227]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3663ada128dsm16367388f8f.117.2024.06.26.09.49.43 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 26 Jun 2024 09:49:43 -0700 (PDT) Message-ID: <9af34a6b-ca56-4a64-8aa6-ade65f109288@redhat.com> Date: Wed, 26 Jun 2024 18:49:42 +0200 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 v1 2/2] mm/migrate: move NUMA hinting fault folio isolation + checks under PTL To: Zi Yan Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Andrew Morton References: <20240620212935.656243-1-david@redhat.com> <20240620212935.656243-3-david@redhat.com> <0F4ABC1D-7A26-4AE2-BCAA-3EA906FB13A7@nvidia.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: <0F4ABC1D-7A26-4AE2-BCAA-3EA906FB13A7@nvidia.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 21.06.24 22:48, Zi Yan wrote: > On 21 Jun 2024, at 16:18, David Hildenbrand wrote: > >> On 21.06.24 15:44, Zi Yan wrote: >>> On 20 Jun 2024, at 17:29, David Hildenbrand wrote: >>> >>>> Currently we always take a folio reference even if migration will not >>>> even be tried or isolation failed, requiring us to grab+drop an additional >>>> reference. >>>> >>>> Further, we end up calling folio_likely_mapped_shared() while the folio >>>> might have already been unmapped, because after we dropped the PTL, that >>>> can easily happen. We want to stop touching mapcounts and friends from >>>> such context, and only call folio_likely_mapped_shared() while the folio >>>> is still mapped: mapcount information is pretty much stale and unreliable >>>> otherwise. >>>> >>>> So let's move checks into numamigrate_isolate_folio(), rename that >>>> function to migrate_misplaced_folio_prepare(), and call that function >>>> from callsites where we call migrate_misplaced_folio(), but still with >>>> the PTL held. >>>> >>>> We can now stop taking temporary folio references, and really only take >>>> a reference if folio isolation succeeded. Doing the >>>> folio_likely_mapped_shared() + golio isolation under PT lock is now similar >>>> to how we handle MADV_PAGEOUT. >>>> >>>> While at it, combine the folio_is_file_lru() checks. >>>> >>>> Signed-off-by: David Hildenbrand >>>> --- >>>> include/linux/migrate.h | 7 ++++ >>>> mm/huge_memory.c | 8 ++-- >>>> mm/memory.c | 9 +++-- >>>> mm/migrate.c | 81 +++++++++++++++++++---------------------- >>>> 4 files changed, 55 insertions(+), 50 deletions(-) >>> >>> LGTM. Reviewed-by: Zi Yan >>> >>> One nit below: >>> >>> >>> >>>> diff --git a/mm/huge_memory.c b/mm/huge_memory.c >>>> index fc27dabcd8e3..4b2817bb2c7d 100644 >>>> --- a/mm/huge_memory.c >>>> +++ b/mm/huge_memory.c >>>> @@ -1688,11 +1688,13 @@ vm_fault_t do_huge_pmd_numa_page(struct vm_fault *vmf) >>>> if (node_is_toptier(nid)) >>>> last_cpupid = folio_last_cpupid(folio); >>>> target_nid = numa_migrate_prep(folio, vmf, haddr, nid, &flags); >>>> - if (target_nid == NUMA_NO_NODE) { >>>> - folio_put(folio); >>>> + if (target_nid == NUMA_NO_NODE) >>>> + goto out_map; >>>> + if (migrate_misplaced_folio_prepare(folio, vma, target_nid)) { >>>> + flags |= TNF_MIGRATE_FAIL; >>>> goto out_map; >>>> } >>>> - >>>> + /* The folio is isolated and isolation code holds a folio reference. */ >>>> spin_unlock(vmf->ptl); >>>> writable = false; >>>> >>>> diff --git a/mm/memory.c b/mm/memory.c >>>> index 118660de5bcc..4fd1ecfced4d 100644 >>>> --- a/mm/memory.c >>>> +++ b/mm/memory.c >>> >>> >>> >>>> @@ -5345,10 +5343,13 @@ static vm_fault_t do_numa_page(struct vm_fault *vmf) >>>> else >>>> last_cpupid = folio_last_cpupid(folio); >>>> target_nid = numa_migrate_prep(folio, vmf, vmf->address, nid, &flags); >>>> - if (target_nid == NUMA_NO_NODE) { >>>> - folio_put(folio); >>>> + if (target_nid == NUMA_NO_NODE) >>>> + goto out_map; >>>> + if (migrate_misplaced_folio_prepare(folio, vma, target_nid)) { >>>> + flags |= TNF_MIGRATE_FAIL; >>>> goto out_map; >>>> } >>> >>> These two locations are repeated code, maybe just merge the ifs into >>> numa_migrate_prep(). Feel free to ignore if you are not going to send >>> another version. :) >> >> I went back and forth a couple of times and >> >> a) Didn't want to move numa_migrate_prep() into >> migrate_misplaced_folio_prepare(), because having that code in >> mm/migrate.c felt a bit odd. > > I agree after checking the actual code, since the code is just > updating NUMA fault stats and checking where the folio should be. > >> >> b) Didn't want to move migrate_misplaced_folio_prepare() because I enjoy >> seeing the migrate_misplaced_folio_prepare() and >> migrate_misplaced_folio() calls in the same callercontext. >> >> I also considered renaming numa_migrate_prep(), but wasn't really able to come up with a good name. > > How about numa_migrate_check()? Since it tells whether a folio should be > migrated or not. > >> >> But maybe a) is not too bad? >> >> We'd have migrate_misplaced_folio_prepare() consume &flags and &target_nid, and perform the "flags |= TNF_MIGRATE_FAIL;" internally. >> >> What would be your take? > > I would either rename numa_migrate_prep() or just do nothing. I have to admit > that the "prep" and "prepare" in both function names motivated me to propose > the merge, but now the actual code tells me they should be separate. Let's leave it like that for now. Renaming to numa_migrate_check() makes sense, and likely moving more numa handling stuff in there. Bit I yet have to figure out why some of the memory.c vs. huge_memory.c code differences exist, so we can unify them. For example, why did 33024536bafd9 introduce slightly different last_cpupid handling in do_huge_pmd_numa_page(), whereby it seems like some subtle difference in handling NUMA_BALANCING_MEMORY_TIERING? Maybe I am missing something obvious. :) -- Cheers, David / dhildenb