From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 83A02C982FA for ; Wed, 23 Sep 2026 11:20:38 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 70A816B008A; Wed, 23 Sep 2026 07:20:37 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 6BA9C6B008C; Wed, 23 Sep 2026 07:20:37 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 5AA246B0092; Wed, 23 Sep 2026 07:20:37 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0015.hostedemail.com [216.40.44.15]) by kanga.kvack.org (Postfix) with ESMTP id 35AC16B008A for ; Wed, 23 Sep 2026 07:20:37 -0400 (EDT) Received: from smtpin27.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay02.hostedemail.com (Postfix) with ESMTP id A9BA9120752 for ; Wed, 23 Sep 2026 11:20:36 +0000 (UTC) X-FDA: 85244784072.27.F47769C Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf07.hostedemail.com (Postfix) with ESMTP id F15C840007 for ; Wed, 23 Sep 2026 11:20:34 +0000 (UTC) Authentication-Results: imf07.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=eqUA7PDy; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf07.hostedemail.com: domain of david@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=david@kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1790162435; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=T2qpMYdJaz4fAIUSyChAch/nEGjd4wrkfVeBx+WLlqE=; b=TmOIAn1lyixRheBL1p5RmhpQPe7H8l3tOHXiAPYJfu3PWb7IPhRP4QBRWXERxFvE7saiuM HAdv3jTyXPoRb3khny788QmjfeZpkgPdNIFN6bvfpHGfuucSJicKnfbF+AVNnESHA73/eC V14N0WCe02Pg5SZ3VP+zZxLii7PvPWI= ARC-Authentication-Results: i=1; imf07.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=eqUA7PDy; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf07.hostedemail.com: domain of david@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=david@kernel.org ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1790162435; b=ruqY8yjex+z+47is+ZVAq9Ry/+fUwTq6nU08VwrqlO1EHYRNpFRjsUBkruAx1aZgQ7IpKZ dBX+ggOqYxqhZCURym4uoEFuPlDCtODgCwBJn60g8f78cUcG9a5ReI5vDC90Dy0NlTuKJ1 FXHiTxrwhfy67b6DDTylPCPPVBMCay8= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id 782316020F; Wed, 23 Sep 2026 11:20:34 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 753231F00899; Wed, 23 Sep 2026 11:20:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1790162434; bh=T2qpMYdJaz4fAIUSyChAch/nEGjd4wrkfVeBx+WLlqE=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=eqUA7PDy7+NmO2fWXgUCRHcoL1aj0mu7vVZbrUFneUJJPmUViNaxyE8PJHIGrPZE2 9n9iqQHrvoL62Kl/NT0aYPUgPpVaeyliUeCz2vSWumqe/atTO/49JC7WOOJmCFgwHY SuMNbNxXgRR1u1CAXxK9vqVkFSzR2UEekJh+lsaewxP5/wMtTjFJRA4xXTTqp4RAyj x/OeR5zlFZRPdsS2hm+RasuEnMhYgHxzxaUj2mVV+uY1mKxM9kgtVH7VYXWhV7YCTw gXWF7hnk/6+zaIqacb5EF1hM0zzkfQGUmqZ9En+UTSOxscNRAzmk2ySFf05tQGqKsc BusVO1RhbN62g== Message-ID: <7f6eb404-8139-4208-88eb-03ea8a4bf3a9@kernel.org> Date: Wed, 23 Sep 2026 13:20:23 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RESEND v7 11/29] mm: split PMD swap entries into PTE swap entries To: Usama Arif , Andrew Morton , chrisl@kernel.org, kasong@tencent.com, ljs@kernel.org, ziy@nvidia.com, linux-mm@kvack.org Cc: ying.huang@linux.alibaba.com, Baoquan He , willy@infradead.org, youngjun.park@lge.com, hannes@cmpxchg.org, riel@surriel.com, shakeel.butt@linux.dev, alex@ghiti.fr, kas@kernel.org, baohua@kernel.org, dev.jain@arm.com, baolin.wang@linux.alibaba.com, Nico Pache , "Liam R. Howlett" , ryan.roberts@arm.com, Vlastimil Babka , lance.yang@linux.dev, linux-kernel@vger.kernel.org, nphamcs@gmail.com, shikemeng@huaweicloud.com, yosry@kernel.org, qi.zheng@linux.dev, luizcap@redhat.com, kernel-team@meta.com References: <20260914122950.3283997-1-usama.arif@linux.dev> <20260914122950.3283997-12-usama.arif@linux.dev> 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: <20260914122950.3283997-12-usama.arif@linux.dev> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Stat-Signature: bnk6obq9j6buwg9y313uftofi8han7kw X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: F15C840007 X-HE-Tag: 1790162434-477038 X-HE-Meta: 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 eXXWUmGh EAZqUcGr5oFFnB4lU8NfodF4aDIwL5rxgB4rXzlE2sdgEPVWH+y91d1uWNAc7f5wx92z3RM3cvUvCnKNz1FYu1GYud/9R5IWFLVF9oWqr29sFmgb8E+Y170I8xzVcyrL/2Ud9kWc3jF7X1pW6zjwQ/TBxMLgbutU4rv9ALZWxTkA6N9fmkPDelyiaeM+ALHOzTLhAsTPyUxp6ydt3AOuz56tBIjgDmvQ+X8aXJZPinSvy+DHXTmbpwby6+/x32ulOLd/i Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 9/14/26 14:28, Usama Arif wrote: > Once a PMD can hold a swap entry, everything that splits a PMD - mprotect() > or munmap() over part of the range, MADV_FREE, a pagewalk with no PMD > handler - has to be able to split that entry too, or the callers that rely > on split_huge_pmd() to hand them a PTE table would find the PMD unchanged. > > No reference counting is needed: a swap entry pins no folio, and swap_map > is already one per slot, so the PTEs simply take over what the PMD held. > > The migration-only entry point cannot reach the new branch, because > page_vma_mapped_walk() never hands back a swap PMD for the folio being > migrated. Warn if that ever changes, and force the regular split anyway, > since the branch leaves folio and page uninitialised. > > Test the pre-split old_pmd rather than re-reading *pmd in the trailing > folio_remove_rmap_pmd() gate, so every entry-type test in the function > interrogates the same snapshot. That part is cosmetic: pmdp_invalidate() > leaves the PMD present as far as software is concerned. > > Signed-off-by: Usama Arif > --- > mm/huge_memory.c | 36 +++++++++++++++++++++++++++++++++++- > 1 file changed, 35 insertions(+), 1 deletion(-) > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index 873887aed0bc2..0e347a545588c 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -3304,6 +3304,21 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd, > folio_add_anon_rmap_ptes(folio, page, HPAGE_PMD_NR, > vma, haddr, rmap_flags); > } > + } else if (pmd_is_swap_entry(*pmd)) { > + /* > + * A PMD swap entry has no page, so it cannot be turned into > + * PTE migration entries. page_vma_mapped_walk() never hands > + * one back for the folio being migrated, so this should not > + * happen; warn, but also force the regular split so that a > + * broken invariant cannot make the code below dereference the > + * uninitialised folio and page. I disagree with the force (and the comment). We cannot make each and every assertion that never happens (unless someone messes up real bad and would find this during early testing) have recovery code. The real bug would be calling split_pmd_to_migration_entries() with something unexpected. See my reply to #10 where we bail out earlier > + */ > + VM_WARN_ON_ONCE(use_migration_entries); > + use_migration_entries = false; Can we just have on the beginning of the function a check that use_migration_entries is only ever set on present PMDs or device-private entries. > + old_pmd = *pmd; > + soft_dirty = pmd_swp_soft_dirty(old_pmd); > + uffd_wp = pmd_swp_uffd(old_pmd); > + anon_exclusive = pmd_swp_exclusive(old_pmd); > } else { > /* > * Up to this point the pmd is present and huge and userland has > @@ -3440,6 +3455,25 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd, > VM_WARN_ON(!pte_none(ptep_get(pte + i))); > set_pte_at(mm, addr, pte + i, entry); > } > + } else if (pmd_is_swap_entry(old_pmd)) { > + const softleaf_t old_entry = softleaf_from_pmd(old_pmd); > + pte_t pte_swp_entry; > + swp_entry_t entry; > + > + for (i = 0, addr = haddr; i < HPAGE_PMD_NR; > + i++, addr += PAGE_SIZE) { Just squeeze it into one line like the other instances. > + entry = swp_entry(swp_type(old_entry), > + swp_offset(old_entry) + i); Didn't we have a helper to advance by a delta? Ah, yes, pte_move_swp_offset(). I guess one could construct the initial pte and then advance one by one through pte_move_swp_offset(). Won't remove a lot of code, though, so just a thought. Apart from that LGTM. -- Cheers, David