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[2003:d8:2f12:1b00:5d6b:db26:e2b7:12]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3a6e80fed75sm3939229f8f.66.2025.06.25.00.49.49 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 25 Jun 2025 00:49:49 -0700 (PDT) Message-ID: <6bda0de6-1ade-40c9-aa52-16bc02d98bee@redhat.com> Date: Wed, 25 Jun 2025 09:49:48 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 0/2] fix MADV_COLLAPSE issue if THP settings are disabled To: Lorenzo Stoakes Cc: Hugh Dickins , Baolin Wang , akpm@linux-foundation.org, ziy@nvidia.com, Liam.Howlett@oracle.com, npache@redhat.com, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, zokeefe@google.com, shy828301@gmail.com, usamaarif642@gmail.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <75c02dbf-4189-958d-515e-fa80bb2187fc@google.com> <9cb94544-f65a-4394-b1e2-bfb226ead31c@redhat.com> <8691d74b-67ee-4e26-81ac-f6bf1725361e@redhat.com> <3b6db0c3-aef3-4a21-a154-6aafd639dbc7@lucifer.local> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam11 X-Rspam-User: X-Rspamd-Queue-Id: 1140240005 X-Stat-Signature: oqqfoyujicbb658jejzukt8qxtmq3zm7 X-HE-Tag: 1750837793-748096 X-HE-Meta: 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 n3pjNNQB hZO168vyTFMA2bfdkRr0Og41DdfF09TNVSMVZqRyCzv9gsSSZ77/FfegmiALRpqKtNSWxrS8qGDARXVvt1jkXvkumQ76zIuPdCkft4lBhapb8JDJ6a9pWlD19KyyPI5BGX+35bpd0BgmhJhKr3Qhzqp2n6DpIuSfaIbDIONjPHCahrQUVzB78vBN0SCDGpriuhxD3USZ7l9YZfa8BpB+rnvDrC7W/ZLHol0VhBShhWU2ktszg7Q/z+tjcOa5BuP+fq4Wf1psnPJx7bvot0ndWL23shyFK9AVT2ld8FAlItaMCgcEW1hh6iIFg7e288kzMwdOyOdk+Gr6h+Jg3mF1BZjePPHKxHXp2PmBS8hVYhS9cRDTvB5e2AE3Lp3JiybdZsnfogLgl1g/BQy8UrDF9Z0G92wE6X02uHA+cDw1Xw6IzxTLPmCmvhOGikrP5LAToWMQ76NuWg7ByzXY= 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: List-Subscribe: List-Unsubscribe: On 25.06.25 09:42, Lorenzo Stoakes wrote: > On Wed, Jun 25, 2025 at 09:36:53AM +0200, David Hildenbrand wrote: >> On 25.06.25 09:30, Lorenzo Stoakes wrote: >>> I _guarantee_ you that's what nearly everybody except a handful of people will >>> expect. >> >> I know, See my other mail, the problem is rather if there is no somebody >> relying on never+MADV_COLLAPSE from doing the MADV_COLLAPSE-documented >> thing. >> >> It's a mess. > > Well now we have an almost philosophical debate - we have different sets of > users, 99% of whom believe the uAPI is X, and 1% of whom believe it is Y. > > Now what is the uAPI? What is 'breaking userspace'? :) Yeah, that's why I mentioned that I think we broke "something" when we changed the semantics. But that breakage probably only affects real corner cases (debugging, customer workarounds). I think the whole use case of using MADV_COLLAPSE to completely control THP allocation in a system is otherwise pretty hard to achieve, if there is no other way to tame THP allocation through page faults+khugepaged. Mess. -- Cheers, David / dhildenb