From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B5FD73DE426 for ; Wed, 23 Sep 2026 13:34:19 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790170460; cv=none; b=D6djrNd0sQ+JGitWYThyFvT46SJfxJQhRiCBVcYqSuRlY3HB5v3YApyq/F7g6KXgQqz+oPrlq3ULbn4/XbaXTFq740YpjAgLqQTMNhl7eTz0yRka5jHfy53Cu2i6DjsGiPR35Gagpyn3EqlSazQuiyoxDZ9xRY4LTga2g+5UDHY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790170460; c=relaxed/simple; bh=DTpE7gvMB7JXTY0SV2eGfql2vWXaQWIIR+pksHrMaCA=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=BABtdhTRL9Eez89cv/ytFkfTChrIRJQu5nxt3uwG0zzdFKGRBKFKw85qCyx2hqKsImf6hhEV0UdQK63EbJVlGiw+BO3Uf3uBbHmrT0+m+c2yLM1jICM4XSZNONi21yyGKQQvQLmgA8anEjXCCZ3RAwyUPGv+ogH9QpvDLCqreYo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=LwVkJj9Z; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="LwVkJj9Z" Received: by smtp.kernel.org (Postfix) with ESMTPSA id CB1AC1F000FF; Wed, 23 Sep 2026 13:34:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1790170459; bh=nAi96pIQ95HWh44XRESIidPNe1NFI5clCoocx23jiPE=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=LwVkJj9ZkDQNHUczf9zcG7g0DgTpgrnyciNJ/Cx7aktOA81IDL4565Pa4ewbNgbnL sOxlBJ0HEeSge6kIxE/QzVDN5gDP0zv/C3w3Zablx/uNLD1Tw42b1DihXctbcdWxvA qEAZu/JL0E0D42ihlsjAJDN7CWFYRBQ5uIcV2gu0bQShATr7as45XPupetHkHlLoAE UaEbw5YtE8p2mo6O0YDwAOTETtZwfbe50Qx4/bcBIf6wGFN2Db7/5+qGLWgFOlj8k/ l2XE3/dkDQ9HcGI6hM+MbeGmMg24gbbhpHiS7j91lf3l8I+pmVLM/e+UecWuYd1O/i C07+7kOLqzv6g== Message-ID: <63f49a8b-cabf-4b93-a7e2-76b62c463a90@kernel.org> Date: Wed, 23 Sep 2026 15:34:11 +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 v3 11/12] mm/collapse: declare the collapse interface in collapse.h To: Kiryl Shutsemau , Andrew Morton , Lorenzo Stoakes , Zi Yan , Baolin Wang Cc: "Kiryl Shutsemau (Meta)" , linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@meta.com, "Liam R. Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Usama Arif , Vlastimil Babka , Jann Horn References: <20260916093145.4022188-1-kirill@shutemov.name> <20260916093145.4022188-12-kirill@shutemov.name> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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 B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzS5EYXZpZCBIaWxk ZW5icmFuZCAoQ3VycmVudCkgPGRhdmlkQGtlcm5lbC5vcmc+wsGQBBMBCAA6AhsDBQkmWAik AgsJBBUKCQgCFgICHgUCF4AWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaYJt/AIZAQAKCRBN 3hD3AP+DWriiD/9BLGEKG+N8L2AXhikJg6YmXom9ytRwPqDgpHpVg2xdhopoWdMRXjzOrIKD g4LSnFaKneQD0hZhoArEeamG5tyo32xoRsPwkbpIzL0OKSZ8G6mVbFGpjmyDLQCAxteXCLXz ZI0VbsuJKelYnKcXWOIndOrNRvE5eoOfTt2XfBnAapxMYY2IsV+qaUXlO63GgfIOg8RBaj7x 3NxkI3rV0SHhI4GU9K6jCvGghxeS1QX6L/XI9mfAYaIwGy5B68kF26piAVYv/QZDEVIpo3t7 /fjSpxKT8plJH6rhhR0epy8dWRHk3qT5tk2P85twasdloWtkMZ7FsCJRKWscm1BLpsDn6EQ4 jeMHECiY9kGKKi8dQpv3FRyo2QApZ49NNDbwcR0ZndK0XFo15iH708H5Qja/8TuXCwnPWAcJ DQoNIDFyaxe26Rx3ZwUkRALa3iPcVjE0//TrQ4KnFf+lMBSrS33xDDBfevW9+Dk6IISmDH1R HFq2jpkN+FX/PE8eVhV68B2DsAPZ5rUwyCKUXPTJ/irrCCmAAb5Jpv11S7hUSpqtM/6oVESC 3z/7CzrVtRODzLtNgV4r5EI+wAv/3PgJLlMwgJM90Fb3CB2IgbxhjvmB1WNdvXACVydx55V7 LPPKodSTF29rlnQAf9HLgCphuuSrrPn5VQDaYZl4N/7zc2wcWM7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: <20260916093145.4022188-12-kirill@shutemov.name> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 9/16/26 11:31, Kiryl Shutsemau wrote: > From: "Kiryl Shutsemau (Meta)" > > A collapse takes four calls: > > - collapse_control_init() - set up the control a caller carries; > - collapse_scan_pmd() - scan one PTE table, under mmap_lock; > - collapse_run_pmd() - collapse what the scan found, no mmap_lock; As discussed, having a single collapse_pmd() function might be cleaner if that's easily possible. collapse_pmd() > - collapse_control_release() - done with the control. > And as discussed, I hope we can just get rid of a release function that's not actually supposed to release anything right now (unless I was missing an update in one of the patches). > All four are static in khugepaged.c, as are collapse_possible_orders(), > which says what a VMA allows, and the revalidate a caller needs once a > collapse has given the mmap_lock up. No other file can ask for a collapse > without them. > > Declare them in collapse.h, with a comment stating the order they are > called in and who holds the lock over each step. Each function says > what it needs and what it does where it is defined. > > hugepage_vma_revalidate() becomes collapse_vma_revalidate(): it is part of > what a collapse offers now, not a helper of the daemon. Is it just me or is collapse_vma_revalidate() an odd part of this interface? You'd expect a matching function that performs the initial validation on a given vma. Maybe we should have a orders = collapse_vma_validate(vma) that really just wraps collapse_possible_orders(), an expose that instead to the collapse users? So they'd use collapse_vma_validate() to then call collapse_vma_revalidate() after temporarily dropping the mmap lock? [...] > -static enum scan_result hugepage_vma_revalidate(struct mm_struct *mm, unsigned long address, > +enum scan_result collapse_vma_revalidate(struct mm_struct *mm, unsigned long address, > bool expect_anon, struct vm_area_struct **vmap, > struct collapse_control *cc, unsigned int order) > { > @@ -1264,7 +1264,7 @@ static enum scan_result collapse_huge_page(struct mm_struct *mm, > } > > mmap_read_lock(mm); > - result = hugepage_vma_revalidate(mm, pmd_addr, /*expect_anon=*/ true, > + result = collapse_vma_revalidate(mm, pmd_addr, /*expect_anon=*/ true, > &vma, cc, order); > if (result != SCAN_SUCCEED) { > mmap_read_unlock(mm); > @@ -1299,7 +1299,7 @@ static enum scan_result collapse_huge_page(struct mm_struct *mm, > * mmap_lock. > */ > mmap_write_lock(mm); > - result = hugepage_vma_revalidate(mm, pmd_addr, /*expect_anon=*/ true, > + result = collapse_vma_revalidate(mm, pmd_addr, /*expect_anon=*/ true, > &vma, cc, order); > if (result != SCAN_SUCCEED) > goto out_up_write; > @@ -2741,7 +2741,8 @@ static enum scan_result collapse_scan_file(struct mm_struct *mm, > return result; > } > > -static void collapse_control_init(struct collapse_control *cc) > +/* Set up a control before its first scan; cc->policy is the caller's to fill */ Kerneldoc please. Applies to the other ones exposed as part of the same interface as well. -- Cheers, David