From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (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 BAC95225390 for ; Wed, 28 Jan 2026 16:38:45 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769618327; cv=none; b=cv4VaDq9aT83L/j+l9zoZbn0KmdVa+zTrNM770P9+ijRAmbe/pm2kqpPRbQQXBJ8GvJ3iZm0fr4VakTT3MiTBGFilmaDFZqxdzjP/cRbXSADwpXl3kbZe3g0NtxsCe/YM21pFAbtH55FE2jNW+APqDFE1zmONZKNCX2lp0tG78o= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769618327; c=relaxed/simple; bh=oYpywg6wSKKfqKMO9drAZK+XQSP+GwNWRgfyOXjs4ME=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=PbHh2Rb2qxENQA35wM2DHmzd3/Ik8g+D6WAW4kINAwFxY1906hToyEr493ohh/89Ry53Mm86W9KtIYcAnDn8VsYss+8tZGj5vXyezI5yoXpTlNdJtMiUn84i2pvi9YqebYG5P/VvvuywJXpUvnaGKLtl6ZIio92T+3Mw5I4vlKM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=M9xIHcZE; dkim=pass (2048-bit key) header.d=redhat.com header.i=@redhat.com header.b=XmAY1Iju; arc=none smtp.client-ip=170.10.129.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="M9xIHcZE"; dkim=pass (2048-bit key) header.d=redhat.com header.i=@redhat.com header.b="XmAY1Iju" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1769618324; h=from:from: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; bh=vvwUtKzwHdNf28qH621RfDijiiFJTykMerMvhScCt2E=; b=M9xIHcZEjNFehXEy6S+I7J9kZ3LLtmVMvFUp6dYWBbGv5l0BIhet7K6+3BVq+O1wHh3VaZ y2kdHgiscnStUJR9/hYgvhnSzEdq7lus3XWjevpuCPADCc7zaFnczrU2GsQ3HTzRfSwFfJ nXpvHmxi9/xKNOjEgOvyLlYLiVIAmq4= Received: from mail-oa1-f72.google.com (mail-oa1-f72.google.com [209.85.160.72]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-375-5oSyZB8aOlOeCQ3kbpd1wg-1; Wed, 28 Jan 2026 11:38:43 -0500 X-MC-Unique: 5oSyZB8aOlOeCQ3kbpd1wg-1 X-Mimecast-MFC-AGG-ID: 5oSyZB8aOlOeCQ3kbpd1wg_1769618323 Received: by mail-oa1-f72.google.com with SMTP id 586e51a60fabf-4088136faccso12058026fac.2 for ; Wed, 28 Jan 2026 08:38:43 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=google; t=1769618322; x=1770223122; darn=vger.kernel.org; h=content-transfer-encoding:in-reply-to:content-language:from :references:cc:to:subject:user-agent:mime-version:date:message-id :from:to:cc:subject:date:message-id:reply-to; bh=vvwUtKzwHdNf28qH621RfDijiiFJTykMerMvhScCt2E=; b=XmAY1IjuKA9IaI8BQaXAdj2QtlWaeyod/ftYka/ANmqGO3kgKmtQaqqCRGoDrdStJw CsEFsuPMJLA/g2VFpYMfKVYcnIHxMtU25+YK9H+TqtXIg40y5C2vbq9B8g0eVlensS6O o1Bh+0SDCU0xQcTUMavTlDD/GeVUg1yEw3sSO8rkIy94gsawxXyVYugE7hR+sk48CA9e 7KdvCXfcq3eWvzAH7ByTyCA5jubRteUYW4LExVUUyMf6bugLdLP0BTKkqSlVYTQhryVs 1bfplfWfm2JHxMHcrYwgOHslczBg/zUcZEHo4OdJ38lqd2iE9O96raguCkhxpzUYMoes v9ow== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1769618322; x=1770223122; h=content-transfer-encoding:in-reply-to:content-language:from :references:cc:to:subject:user-agent:mime-version:date:message-id :x-gm-gg:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=vvwUtKzwHdNf28qH621RfDijiiFJTykMerMvhScCt2E=; b=XeO1AfYZXn/q1V2Q7XzH1VfnHaOBAzkTWiAScWsrMBptWY4rhcEe2kPsCz/WjnBMC4 Q6wLrloAT2pnmJWfCRCtbWgRppgzD/b9aNveL2ffvPv9lL3gTytTc07yru+Xz/mF0GmR mPRJ/NqU850Y9bl7Mgw+N2vPOlE8I9DCUUKJy5Fv9803zpZOqwImUyoeYSW0rJehq+FE 5wZjVyttKz2KL1M2Xf5A51CPEPC3PGtAAYSQSz3ueTF7tshAgdoB928BZRN89dr2Hg43 O68b/EVtgh4S+FL9cqHJlAiJYE1PHT2n5wCT/GkRB8qBw0LoC3o4JKTC0Z+qDNjWg0MT XKYg== X-Forwarded-Encrypted: i=1; AJvYcCUteSeXgTUAnvTmRqlwCX/u04O4S0JcJtLAtjI82LohtCBsMcn3uu+p6L4iQIg1bRvnlmvHiz3IhEDBHUE=@vger.kernel.org X-Gm-Message-State: AOJu0YxNwQrqv3ueiaiuME4EOV65SGI9dvepFefFjfvnRQLCrDQXvw18 dU8W+U0nTJ1BRBA5kbrhaFf4drevdnYuQHmiHn6/xhnt/xzQjpe6oPXCnjrbOpbVRZLmBZGu/WM 7onTVg/tKBhfjufn1AZZojgxOVOVtEztP9QiLrjDthI5/rl7SazZS852voya7pGqzcw== X-Gm-Gg: AZuq6aJ8v8kCDaQj+uWsueLxsTTWydLC3Aw2vkxhhADFBYhWcSP3JmUs3JAOjeJYMa0 fq8WYkfdZD/ne0lCmKGaqtSeUfHuuB8SdYYW/GARPtcUcHtiGskHX0Lx5AZwSeAAsE9hie7brqe /9FQAdA1DDTDahUcGZ5wZLhOko877yfhGHKcxTRQrVOCvz0NJqoUDrDxBMHu/G68QwywD/o1RzW c9YX3rVtdQ+wUUqcdUsLs5VQOdB2x7cLkA+KlNxDcGcKaaTy3xDV93mhv3beweoOKQigdOen1KN GPLxE87ogjd1ebN+JvRWtlPpDZMHWZS+Q3ale+tnwg8iLcRZnfHC+2RCXtpQkBDC0zOS6F2yiPv jZn7LMYb7qByjU789sg== X-Received: by 2002:a05:6870:6f03:b0:3ec:3aa1:84d2 with SMTP id 586e51a60fabf-4093fc716demr3763734fac.11.1769618322481; Wed, 28 Jan 2026 08:38:42 -0800 (PST) X-Received: by 2002:a05:6870:6f03:b0:3ec:3aa1:84d2 with SMTP id 586e51a60fabf-4093fc716demr3763682fac.11.1769618320931; Wed, 28 Jan 2026 08:38:40 -0800 (PST) Received: from ?IPV6:2601:282:1c83:9aa0::56cf? ([2601:282:1c83:9aa0::56cf]) by smtp.gmail.com with ESMTPSA id 586e51a60fabf-409570f63b4sm2077985fac.3.2026.01.28.08.38.38 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 28 Jan 2026 08:38:40 -0800 (PST) Message-ID: Date: Wed, 28 Jan 2026 09:38:37 -0700 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-unstable v14 03/16] introduce collapse_single_pmd to unify khugepaged and madvise_collapse To: linux-mm@kvack.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, akpm@linux-foundation.org Cc: david@kernel.org, lorenzo.stoakes@oracle.com, ziy@nvidia.com, baolin.wang@linux.alibaba.com, Liam.Howlett@oracle.com, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, lance.yang@linux.dev, vbabka@suse.cz, rppt@kernel.org, surenb@google.com, mhocko@suse.com, corbet@lwn.net, rostedt@goodmis.org, mhiramat@kernel.org, mathieu.desnoyers@efficios.com, matthew.brost@intel.com, joshua.hahnjy@gmail.com, rakie.kim@sk.com, byungchul@sk.com, gourry@gourry.net, ying.huang@linux.alibaba.com, apopple@nvidia.com, jannh@google.com, pfalcato@suse.de, jackmanb@google.com, hannes@cmpxchg.org, willy@infradead.org, peterx@redhat.com, wangkefeng.wang@huawei.com, usamaarif642@gmail.com, sunnanyong@huawei.com, vishal.moola@gmail.com, thomas.hellstrom@linux.intel.com, yang@os.amperecomputing.com, kas@kernel.org, aarcange@redhat.com, raquini@redhat.com, anshuman.khandual@arm.com, catalin.marinas@arm.com, tiwai@suse.de, will@kernel.org, dave.hansen@linux.intel.com, jack@suse.cz, cl@gentwo.org, jglisse@google.com, zokeefe@google.com, rientjes@google.com, rdunlap@infradead.org, hughd@google.com, richard.weiyang@gmail.com, David Hildenbrand , shivankg@amd.com References: <20260122192841.128719-1-npache@redhat.com> <20260122192841.128719-4-npache@redhat.com> From: Nico Pache Content-Language: en-US, en-ZM In-Reply-To: <20260122192841.128719-4-npache@redhat.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Hi Andrew, could you please apply the following fixup to avoid potentially using a stale VMA in the new writeback-retry logic for madvise collapse. Thank you! -- Nico ----8<---- commit a9ac3b1bfa926dd707ac3a785583f8d7a0579578 Author: Nico Pache Date: Fri Jan 23 16:32:42 2026 -0700 madvise writeback retry logic fix Signed-off-by: Nico Pache diff --git a/mm/khugepaged.c b/mm/khugepaged.c index 59e5a5588d85..2b054f7d9753 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -2418,6 +2418,14 @@ static enum scan_result collapse_single_pmd(unsigned long addr, mmap_read_unlock(mm); *mmap_locked = false; result = collapse_scan_file(mm, addr, file, pgoff, cc); + + if (!cc->is_khugepaged && result == SCAN_PAGE_DIRTY_OR_WRITEBACK && + mapping_can_writeback(file->f_mapping)) { + const loff_t lstart = (loff_t)pgoff << PAGE_SHIFT; + const loff_t lend = lstart + HPAGE_PMD_SIZE - 1; + + filemap_write_and_wait_range(file->f_mapping, lstart, lend); + } fput(file); if (result != SCAN_PTE_MAPPED_HUGEPAGE) @@ -2840,19 +2848,8 @@ int madvise_collapse(struct vm_area_struct *vma, unsigned long start, *lock_dropped = true; if (result == SCAN_PAGE_DIRTY_OR_WRITEBACK && !triggered_wb) { - struct file *file = get_file(vma->vm_file); - pgoff_t pgoff = linear_page_index(vma, addr); - - if (mapping_can_writeback(file->f_mapping)) { - loff_t lstart = (loff_t)pgoff << PAGE_SHIFT; - loff_t lend = lstart + HPAGE_PMD_SIZE - 1; - - filemap_write_and_wait_range(file->f_mapping, lstart, lend); - triggered_wb = true; - fput(file); - goto retry; - } - fput(file); + triggered_wb = true; + goto retry; } switch (result) { -- 2.52.0 On 1/22/26 12:28 PM, Nico Pache wrote: > The khugepaged daemon and madvise_collapse have two different > implementations that do almost the same thing. > > Create collapse_single_pmd to increase code reuse and create an entry > point to these two users. > > Refactor madvise_collapse and collapse_scan_mm_slot to use the new > collapse_single_pmd function. This introduces a minor behavioral change > that is most likely an undiscovered bug. The current implementation of > khugepaged tests collapse_test_exit_or_disable before calling > collapse_pte_mapped_thp, but we weren't doing it in the madvise_collapse > case. By unifying these two callers madvise_collapse now also performs > this check. We also modify the return value to be SCAN_ANY_PROCESS which > properly indicates that this process is no longer valid to operate on. > > We also guard the khugepaged_pages_collapsed variable to ensure its only > incremented for khugepaged. > > Reviewed-by: Wei Yang > Reviewed-by: Lance Yang > Reviewed-by: Lorenzo Stoakes > Reviewed-by: Baolin Wang > Reviewed-by: Zi Yan > Acked-by: David Hildenbrand > Signed-off-by: Nico Pache > --- > mm/khugepaged.c | 106 +++++++++++++++++++++++++++--------------------- > 1 file changed, 60 insertions(+), 46 deletions(-) > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index fefcbdca4510..59e5a5588d85 100644 > --- a/mm/khugepaged.c > +++ b/mm/khugepaged.c > @@ -2394,6 +2394,54 @@ static enum scan_result collapse_scan_file(struct mm_struct *mm, unsigned long a > return result; > } > > +/* > + * Try to collapse a single PMD starting at a PMD aligned addr, and return > + * the results. > + */ > +static enum scan_result collapse_single_pmd(unsigned long addr, > + struct vm_area_struct *vma, bool *mmap_locked, > + struct collapse_control *cc) > +{ > + struct mm_struct *mm = vma->vm_mm; > + enum scan_result result; > + struct file *file; > + pgoff_t pgoff; > + > + if (vma_is_anonymous(vma)) { > + result = collapse_scan_pmd(mm, vma, addr, mmap_locked, cc); > + goto end; > + } > + > + file = get_file(vma->vm_file); > + pgoff = linear_page_index(vma, addr); > + > + mmap_read_unlock(mm); > + *mmap_locked = false; > + result = collapse_scan_file(mm, addr, file, pgoff, cc); > + fput(file); > + > + if (result != SCAN_PTE_MAPPED_HUGEPAGE) > + goto end; > + > + mmap_read_lock(mm); > + *mmap_locked = true; > + if (collapse_test_exit_or_disable(mm)) { > + mmap_read_unlock(mm); > + *mmap_locked = false; > + return SCAN_ANY_PROCESS; > + } > + result = try_collapse_pte_mapped_thp(mm, addr, !cc->is_khugepaged); > + if (result == SCAN_PMD_MAPPED) > + result = SCAN_SUCCEED; > + mmap_read_unlock(mm); > + *mmap_locked = false; > + > +end: > + if (cc->is_khugepaged && result == SCAN_SUCCEED) > + ++khugepaged_pages_collapsed; > + return result; > +} > + > static unsigned int collapse_scan_mm_slot(unsigned int pages, enum scan_result *result, > struct collapse_control *cc) > __releases(&khugepaged_mm_lock) > @@ -2466,34 +2514,9 @@ static unsigned int collapse_scan_mm_slot(unsigned int pages, enum scan_result * > VM_BUG_ON(khugepaged_scan.address < hstart || > khugepaged_scan.address + HPAGE_PMD_SIZE > > hend); > - if (!vma_is_anonymous(vma)) { > - struct file *file = get_file(vma->vm_file); > - pgoff_t pgoff = linear_page_index(vma, > - khugepaged_scan.address); > - > - mmap_read_unlock(mm); > - mmap_locked = false; > - *result = collapse_scan_file(mm, > - khugepaged_scan.address, file, pgoff, cc); > - fput(file); > - if (*result == SCAN_PTE_MAPPED_HUGEPAGE) { > - mmap_read_lock(mm); > - if (collapse_test_exit_or_disable(mm)) > - goto breakouterloop; > - *result = try_collapse_pte_mapped_thp(mm, > - khugepaged_scan.address, false); > - if (*result == SCAN_PMD_MAPPED) > - *result = SCAN_SUCCEED; > - mmap_read_unlock(mm); > - } > - } else { > - *result = collapse_scan_pmd(mm, vma, > - khugepaged_scan.address, &mmap_locked, cc); > - } > - > - if (*result == SCAN_SUCCEED) > - ++khugepaged_pages_collapsed; > > + *result = collapse_single_pmd(khugepaged_scan.address, > + vma, &mmap_locked, cc); > /* move to next address */ > khugepaged_scan.address += HPAGE_PMD_SIZE; > progress += HPAGE_PMD_NR; > @@ -2799,6 +2822,7 @@ int madvise_collapse(struct vm_area_struct *vma, unsigned long start, > cond_resched(); > mmap_read_lock(mm); > mmap_locked = true; > + *lock_dropped = true; > result = hugepage_vma_revalidate(mm, addr, false, &vma, > cc); > if (result != SCAN_SUCCEED) { > @@ -2809,17 +2833,17 @@ int madvise_collapse(struct vm_area_struct *vma, unsigned long start, > hend = min(hend, vma->vm_end & HPAGE_PMD_MASK); > } > mmap_assert_locked(mm); > - if (!vma_is_anonymous(vma)) { > - struct file *file = get_file(vma->vm_file); > - pgoff_t pgoff = linear_page_index(vma, addr); > > - mmap_read_unlock(mm); > - mmap_locked = false; > + result = collapse_single_pmd(addr, vma, &mmap_locked, cc); > + > + if (!mmap_locked) > *lock_dropped = true; > - result = collapse_scan_file(mm, addr, file, pgoff, cc); > > - if (result == SCAN_PAGE_DIRTY_OR_WRITEBACK && !triggered_wb && > - mapping_can_writeback(file->f_mapping)) { > + if (result == SCAN_PAGE_DIRTY_OR_WRITEBACK && !triggered_wb) { > + struct file *file = get_file(vma->vm_file); > + pgoff_t pgoff = linear_page_index(vma, addr); > + > + if (mapping_can_writeback(file->f_mapping)) { > loff_t lstart = (loff_t)pgoff << PAGE_SHIFT; > loff_t lend = lstart + HPAGE_PMD_SIZE - 1; > > @@ -2829,26 +2853,16 @@ int madvise_collapse(struct vm_area_struct *vma, unsigned long start, > goto retry; > } > fput(file); > - } else { > - result = collapse_scan_pmd(mm, vma, addr, &mmap_locked, cc); > } > - if (!mmap_locked) > - *lock_dropped = true; > > -handle_result: > switch (result) { > case SCAN_SUCCEED: > case SCAN_PMD_MAPPED: > ++thps; > break; > - case SCAN_PTE_MAPPED_HUGEPAGE: > - BUG_ON(mmap_locked); > - mmap_read_lock(mm); > - result = try_collapse_pte_mapped_thp(mm, addr, true); > - mmap_read_unlock(mm); > - goto handle_result; > /* Whitelisted set of results where continuing OK */ > case SCAN_NO_PTE_TABLE: > + case SCAN_PTE_MAPPED_HUGEPAGE: > case SCAN_PTE_NON_PRESENT: > case SCAN_PTE_UFFD_WP: > case SCAN_LACK_REFERENCED_PAGE: