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 BC0F3367B86 for ; Wed, 14 Oct 2026 10:52:25 +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=1791975146; cv=none; b=c3FKncNXQndsazoaBXwd3A3zsYfGXhZVvyi7LdaF6wuEnqADNlIgPY9YnRZeXqme+J4kdeNcX1/zo/NKdJBSVbovkOoJauI4jOiN4oOhNfctiWi37KlI/IDZa1D6bXoT6ZysBivoL2tm93U6Yj554QKLdsUGj7Wnr5tJUNTeb5I= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791975146; c=relaxed/simple; bh=v6Qxe1uVaD9itaT0J7AgCi3k0ua2nbEnaJaRCK24W6U=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=czHAPSJWM4OGe9Rjo67b31AN59yaQgCzLbcUxeKlXSeXoncxZBF1lTvD4xmEI6b10YGZYQy37Jf8lVmjAhkR9fyRomfrw7Q9PsvkSptmZsTQ+hsWfGoW3PL99DuQ6ZmDOnhmVMgiXJFE4UdeXxkD+nMGXD9Svd4cUiQKTqgZCGM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=ALUatxx7; 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="ALUatxx7" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 462021F000FF; Wed, 14 Oct 2026 10:52:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1791975145; bh=A40pvqxsAljXMht0uJoUDXzF1WEP0B00UO/a2qcSq5c=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=ALUatxx7upV3SZkfTnvX3IgE4XE+F0RxjUatM7WzbYQ58SeOSupRbXZp9Rs4KDDqb Yx8oUW/jtDikFJHSuTlvN5n3Q9pyBZundVS5MQjW9e5SRXjsayfxpDyQOihfdJ3GUn 6Kchw16CYAjiKisdIGTDFi2pxpgtZYYmARcaI9bkxGSkpSJOpGXTm0umd7ZSo+Veto 44qiHVrdUirbmIKKUdfVmndXENVDTLdDTTCwJISfk/mjIxWaSgfkCZsgftHVFkvODn fZXUrTMrkJG0nntGG7Mp/FpI/H/aA6k8pY/fBEgtvemb/M3i43UYGXt3JoMgavGHYU gWgh4rgFHLPXg== Message-ID: Date: Wed, 14 Oct 2026 12:52:20 +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] mm/hugetlb: avoid recursive i_mmap_rwsem in PMD sharing To: Li Zhe , "Lorenzo Stoakes (ARM)" Cc: "Jose A. Perez de Azpillaga" , akpm@linux-foundation.org, muchun.song@linux.dev, osalvador@suse.de, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20260930064308.58159-1-lizhe.67@bytedance.com> <9a7c026e-f5f2-40e0-84aa-919c988cc136@bytedance.com> <2b4571c5-8e51-4c91-9d88-11929f200875@kernel.org> <70ea8ee6-6fc5-4209-8cee-362da37f5035@kernel.org> <86de1ee5-be14-4123-b372-b4691cea8e67@bytedance.com> 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: <86de1ee5-be14-4123-b372-b4691cea8e67@bytedance.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 10/14/26 08:39, Li Zhe wrote: > On 10/10/26 2:05 AM, David Hildenbrand (Arm) wrote: >> On 10/9/26 13:52, Lorenzo Stoakes (ARM) wrote: >>> Yeah I don't see why not! I don't think there's anything that needs to be >>> private here. >> Li, see below, can you work with the below? >> >> >> ----8<---- >> From 9e1c0676ea6c9cbcabf91cd8badf81a9d88fd3ef Mon Sep 17 00:00:00 2001 >> From: "Lorenzo Stoakes (ARM)" >> Date: Wed, 29 Jul 2026 18:33:08 +0100 >> Subject: [PATCH] fix >> >> --- >> mm/hugetlb.c | 103 +++++++++++++++++++++++++++++++++++++++------------ >> 1 file changed, 79 insertions(+), 24 deletions(-) >> >> diff --git a/mm/hugetlb.c b/mm/hugetlb.c >> index e93c4d2456aa..88ff2c4ad483 100644 >> --- a/mm/hugetlb.c >> +++ b/mm/hugetlb.c >> @@ -5077,6 +5077,79 @@ static void move_huge_pte(struct vm_area_struct *vma, unsigned long old_addr, >> spin_unlock(dst_ptl); >> } >> >> +/* Returns last address processed */ >> +static unsigned long prealloc_or_move_page_tables(struct vm_area_struct *vma, >> + struct vm_area_struct *new_vma, unsigned long old_addr, >> + unsigned long new_addr, unsigned long len, unsigned long sz, >> + unsigned long last_addr_mask, struct mmu_gather *tlb, >> + bool is_prealloc) >> +{ >> + unsigned long old_end = old_addr + len; >> + struct hstate *h = hstate_vma(vma); >> + struct mm_struct *mm = vma->vm_mm; >> + pte_t *src_pte, *dst_pte; >> + >> + hugetlb_vma_assert_locked(vma); >> + >> + for (; old_addr < old_end; old_addr += sz, new_addr += sz) { >> + src_pte = hugetlb_walk(vma, old_addr, sz); >> + if (!src_pte) { >> + old_addr |= last_addr_mask; >> + new_addr |= last_addr_mask; >> + continue; >> + } >> + if (huge_pte_none(huge_ptep_get(mm, old_addr, src_pte))) >> + continue; >> + >> + if (is_prealloc) { >> + if (!huge_pte_alloc(mm, new_vma, new_addr, sz)) >> + break; >> + continue; >> + } >> + >> + if (huge_pmd_unshare(tlb, vma, old_addr, src_pte)) { >> + old_addr |= last_addr_mask; >> + new_addr |= last_addr_mask; >> + continue; >> + } >> + >> + dst_pte = hugetlb_walk(new_vma, new_addr, sz); >> + if (!dst_pte) >> + break; >> + >> + move_huge_pte(vma, old_addr, new_addr, src_pte, dst_pte, sz); >> + tlb_remove_huge_tlb_entry(h, tlb, src_pte, old_addr); >> + } >> + >> + return old_addr; >> +} >> + >> +/* Returns true if preallocation succeeded across range, otherwise false. */ >> +static bool prealloc_hugetlb_page_tables(struct vm_area_struct *vma, >> + struct vm_area_struct *new_vma, unsigned long old_addr, >> + unsigned long new_addr, unsigned long len, unsigned long sz, >> + unsigned long last_addr_mask) >> +{ >> + unsigned long old_end = old_addr + len; >> + unsigned long addr_end; >> + >> + addr_end = prealloc_or_move_page_tables(vma, new_vma, old_addr, new_addr, >> + len, sz, last_addr_mask, NULL, /*is_prealloc=*/true); >> + >> + return addr_end >= old_end; >> +} >> + >> +/* Returns last processed address. */ >> +static unsigned long __move_hugetlb_page_tables(struct vm_area_struct *vma, >> + struct vm_area_struct *new_vma, unsigned long old_addr, >> + unsigned long new_addr, unsigned long len, unsigned long sz, >> + unsigned long last_addr_mask, struct mmu_gather *tlb) >> +{ >> + i_mmap_assert_write_locked(vma->vm_file->f_mapping); >> + return prealloc_or_move_page_tables(vma, new_vma, old_addr, new_addr, >> + len, sz, last_addr_mask, tlb, /*is_prealloc=*/false); >> +} >> + >> int move_hugetlb_page_tables(struct vm_area_struct *vma, >> struct vm_area_struct *new_vma, >> unsigned long old_addr, unsigned long new_addr, >> @@ -5088,9 +5161,9 @@ int move_hugetlb_page_tables(struct vm_area_struct *vma, >> struct mm_struct *mm = vma->vm_mm; >> unsigned long old_end = old_addr + len; >> unsigned long last_addr_mask; >> - pte_t *src_pte, *dst_pte; >> struct mmu_notifier_range range; >> struct mmu_gather tlb; >> + bool preallocated; >> >> mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, mm, old_addr, >> old_end); >> @@ -5106,30 +5179,12 @@ int move_hugetlb_page_tables(struct vm_area_struct *vma, >> last_addr_mask = hugetlb_mask_last_page(h); >> /* Prevent race with file truncation */ >> hugetlb_vma_lock_write(vma); >> + preallocated = prealloc_hugetlb_page_tables(vma, new_vma, old_addr, >> + new_addr, len, sz, last_addr_mask); >> i_mmap_lock_write(mapping); >> - for (; old_addr < old_end; old_addr += sz, new_addr += sz) { >> - src_pte = hugetlb_walk(vma, old_addr, sz); >> - if (!src_pte) { >> - old_addr |= last_addr_mask; >> - new_addr |= last_addr_mask; >> - continue; >> - } >> - if (huge_pte_none(huge_ptep_get(mm, old_addr, src_pte))) >> - continue; >> - >> - if (huge_pmd_unshare(&tlb, vma, old_addr, src_pte)) { >> - old_addr |= last_addr_mask; >> - new_addr |= last_addr_mask; >> - continue; >> - } >> - >> - dst_pte = huge_pte_alloc(mm, new_vma, new_addr, sz); >> - if (!dst_pte) >> - break; >> - >> - move_huge_pte(vma, old_addr, new_addr, src_pte, dst_pte, sz); >> - tlb_remove_huge_tlb_entry(h, &tlb, src_pte, old_addr); >> - } >> + if (preallocated) >> + old_addr = __move_hugetlb_page_tables(vma, new_vma, old_addr, >> + new_addr, len, sz, last_addr_mask, &tlb); >> >> tlb_flush_mmu_tlbonly(&tlb); >> huge_pmd_unshare_flush(&tlb, vma); >> -- >> 2.55.0 > > Hi David, > > I thought more about the case where the destination page table was > preallocated as a shared PMD. > > I do not think the current move_huge_pte() handles that case very well. The > reason is that it assumes the destination PTE is not part of a shared PMD > page table: it clears the source PTE and then installs that PTE into the > destination. That works when the destination PMD page table is not shared, > because the source removal and destination install have a net-zero effect on > rmap and hugetlb accounting. > > If the destination PTE belongs to a shared PMD, that assumption does not > hold. In that case, I think we should leave the shared destination page > table untouched and treat the operation as a source-side unmap. Otherwise > move_huge_pte() either writes through a shared page table or skips the > source-side unmap accounting. That can make the rmap, hugetlb count and > folio release handling inconsistent with the actual PTE update. > > So I think the change should be roughly: IIUC, what you are saying is: A) If the source table is shared, unshare it. b) If the destination table is shared, there is nothing to do. ? -- Cheers, David