From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-172.mta1.migadu.com (out-172.mta1.migadu.com [95.215.58.172]) (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 69139481B1; Mon, 27 Oct 2025 09:01:04 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1761555666; cv=none; b=OO8mS5YAmf4hG2MTmjam5HbVpH+M8NEijpfh32qSvFAcbQMXX9gFpay1Uz7dyAZTqvIRhokFdWoorvA6k9r+mEcxPiP80gp85LjfxCpDbv3RUtNwp13qyNKep6bn/r0VrMHUc8MtTxWlKVc8w6LVZFlz1UKQRuWPxzk1ao1PGAQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1761555666; c=relaxed/simple; bh=UPiwTkhB/J6BBNQtWBHJvGhNPiYEsm0JTSBHxuibEq8=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=Jr4JlkjsQ4BXtDVjprXQiRPOt+CXh9WBHbKyR/OuenV04GLKG6CRJT14QV4BqMT4XpAP7iEjm8MeIEvGtD/8i2OFHv3tP3gXpMxMnDSMuippRNBK5uDEP0FKpD9KPdNN8JfJ4yok4dPNstHyU+9qDWdfiuStI3urLpBL20fKOwg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=R2MI8qFP; arc=none smtp.client-ip=95.215.58.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="R2MI8qFP" Message-ID: <3aca400f-2fbf-4249-89bc-d683a4e0618d@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1761555662; 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=rZIxJuwgOmBP+ZkdSSAjjhDddv46eR2/PMPkqFr0INA=; b=R2MI8qFPQ6pU7XLsjr2EjSK0mrr2oa8WAxDi7OPjOOAdBPMpW0J9EDxQakGCniq7rcF56/ bbPsAP4TAva0QsNYON1Rg/bEHR36dhrNLVgkH4N11ECbAs79UWe51AIC9WDoPqIJyvwaIn Lg3+8rp3TWZo+4zu0GmV7LT5N4sf1w0= Date: Mon, 27 Oct 2025 17:00:31 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH v12 mm-new 02/15] introduce collapse_single_pmd to unify khugepaged and madvise_collapse To: Nico Pache Cc: david@redhat.com, ziy@nvidia.com, baolin.wang@linux.alibaba.com, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, ryan.roberts@arm.com, dev.jain@arm.com, corbet@lwn.net, rostedt@goodmis.org, mhiramat@kernel.org, mathieu.desnoyers@efficios.com, akpm@linux-foundation.org, baohua@kernel.org, linux-mm@kvack.org, linux-trace-kernel@vger.kernel.org, willy@infradead.org, peterx@redhat.com, wangkefeng.wang@huawei.com, usamaarif642@gmail.com, sunnanyong@huawei.com, linux-kernel@vger.kernel.org, vishal.moola@gmail.com, thomas.hellstrom@linux.intel.com, linux-doc@vger.kernel.org, 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, surenb@google.com, zokeefe@google.com, hannes@cmpxchg.org, rientjes@google.com, mhocko@suse.com, rdunlap@infradead.org, hughd@google.com, richard.weiyang@gmail.com, vbabka@suse.cz, rppt@kernel.org, jannh@google.com, pfalcato@suse.de References: <20251022183717.70829-1-npache@redhat.com> <20251022183717.70829-3-npache@redhat.com> Content-Language: en-US X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Lance Yang In-Reply-To: <20251022183717.70829-3-npache@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT On 2025/10/23 02:37, 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: Baolin Wang > Acked-by: David Hildenbrand > Signed-off-by: Nico Pache > --- Nice cleanup! LGTM. Reviewed-by: Lance Yang > mm/khugepaged.c | 97 ++++++++++++++++++++++++++----------------------- > 1 file changed, 52 insertions(+), 45 deletions(-) > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index 6c4abc7f45cf..36e31d99e507 100644 > --- a/mm/khugepaged.c > +++ b/mm/khugepaged.c > @@ -2370,6 +2370,53 @@ static int collapse_scan_file(struct mm_struct *mm, unsigned long addr, > return result; > } > > +/* > + * Try to collapse a single PMD starting at a PMD aligned addr, and return > + * the results. > + */ > +static int 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; > + int 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 = 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, int *result, > struct collapse_control *cc) > __releases(&khugepaged_mm_lock) > @@ -2440,34 +2487,9 @@ static unsigned int collapse_scan_mm_slot(unsigned int pages, int *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 = 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; > @@ -2781,34 +2803,19 @@ int madvise_collapse(struct vm_area_struct *vma, unsigned long start, > mmap_assert_locked(mm); > memset(cc->node_load, 0, sizeof(cc->node_load)); > nodes_clear(cc->alloc_nmask); > - 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_scan_file(mm, addr, file, pgoff, cc); > - fput(file); > - } else { > - result = collapse_scan_pmd(mm, vma, addr, > - &mmap_locked, cc); > - } > + result = collapse_single_pmd(addr, vma, &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 = collapse_pte_mapped_thp(mm, addr, true); > - mmap_read_unlock(mm); > - goto handle_result; > /* Whitelisted set of results where continuing OK */ > + case SCAN_PTE_MAPPED_HUGEPAGE: > case SCAN_PMD_NULL: > case SCAN_PTE_NON_PRESENT: > case SCAN_PTE_UFFD_WP: