From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id B0AD6309DCB for ; Thu, 22 Jan 2026 07:32:30 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769067156; cv=none; b=oYMEspyThsjy9ZNiNe3FUtY0l4GgGe2iYX7VMqZ+6/imxLT5UqCZ35CYvEFZhLWVjHXukpB9mUtHaJliYW4+whxiGKPQk3SxziQNe/sXOteKPZrCHtQCv/zEL4fl2CxMWX6SFe5eUtGxIbQWJHGGNE/SAk/s8brd1g+cN1n7ODY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769067156; c=relaxed/simple; bh=KcmuuctKoVRzdvo0w87V/MQGLUtGPb/ExJ6gB+GUurw=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=LLSx5qjqKFtezltqiYJ2bPh/aK7x7xzjo+sAe4gOehUI2+rAA8OuueMl0IkJRALQe2VjzK8n1EDq9AkLZG6dmpcpemWWfPRkSQXcDVdZus9N0Aofz5U2HMzfy1zRpEDCJ3gLdnhVyvr/uPqvtOYy57kNLwHw009kXBB5ciTXhRU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id C2D9E1476; Wed, 21 Jan 2026 23:32:20 -0800 (PST) Received: from [10.164.18.63] (MacBook-Pro.blr.arm.com [10.164.18.63]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 977F13F632; Wed, 21 Jan 2026 23:32:23 -0800 (PST) Message-ID: <829b62c8-e3eb-485f-8d7b-01419c841cc8@arm.com> Date: Thu, 22 Jan 2026 13:02:20 +0530 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 2/5] mm/khugepaged: count small VMAs towards scan limit To: Shivank Garg , Andrew Morton , David Hildenbrand , Lorenzo Stoakes Cc: Zi Yan , Baolin Wang , "Liam R . Howlett" , Nico Pache , Ryan Roberts , Barry Song , Lance Yang , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Wei Yang References: <20260118192253.9263-4-shivankg@amd.com> <20260118192253.9263-8-shivankg@amd.com> Content-Language: en-US From: Dev Jain In-Reply-To: <20260118192253.9263-8-shivankg@amd.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 19/01/26 12:52 am, Shivank Garg wrote: > The khugepaged_scan_mm_slot() uses a 'progress' counter to limit the > amount of work performed and consists of three components: > 1. Transitioning to a new mm (+1). > 2. Skipping an unsuitable VMA (+1). > 3. Scanning a PMD-sized range (+HPAGE_PMD_NR). > > Consider a 1MB VMA sitting between two 2MB alignment boundaries: > > vma1 vma2 vma3 > +----------+------+----------+ > |2M |1M |2M | > +----------+------+----------+ > ^ ^ > start end > ^ > hstart,hend Won't such a VMA be skipped by thp_vma_allowable_order()? That internally checks, apart from eligibility by sysfs, that the extent of the VMA can map a hugepage. > > In this case, for vma2: > hstart = round_up(start, HPAGE_PMD_SIZE) -> Next 2MB alignment > hend = round_down(end, HPAGE_PMD_SIZE) -> Prev 2MB alignment > > Currently, since `hend <= hstart`, VMAs that are too small or unaligned > to contain a hugepage are skipped without incrementing 'progress'. > A process containing a large number of such small VMAs will unfairly > consume more CPU cycles before yielding compared to a process with > fewer, larger, or aligned VMAs. > > Fix this by incrementing progress when the `hend <= hstart` condition > is met. > > Additionally, change 'progress' type to `unsigned int` to match both > the 'pages' type and the function return value. > > Suggested-by: Wei Yang > Reviewed-by: Wei Yang > Reviewed-by: Lance Yang > Signed-off-by: Shivank Garg > --- > > Incorporate comment feedback from Lance: > https://lore.kernel.org/linux-mm/6b408736-978a-4d40-adfc-97819951c3a6@linux.dev > > mm/khugepaged.c | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index 984294a16861..93ce39915f4a 100644 > --- a/mm/khugepaged.c > +++ b/mm/khugepaged.c > @@ -2403,7 +2403,7 @@ static unsigned int khugepaged_scan_mm_slot(unsigned int pages, int *result, > struct mm_slot *slot; > struct mm_struct *mm; > struct vm_area_struct *vma; > - int progress = 0; > + unsigned int progress = 0; > > VM_BUG_ON(!pages); > lockdep_assert_held(&khugepaged_mm_lock); > @@ -2447,7 +2447,8 @@ static unsigned int khugepaged_scan_mm_slot(unsigned int pages, int *result, > } > hstart = round_up(vma->vm_start, HPAGE_PMD_SIZE); > hend = round_down(vma->vm_end, HPAGE_PMD_SIZE); > - if (khugepaged_scan.address > hend) { > + if (khugepaged_scan.address > hend || hend <= hstart) { > + /* VMA already scanned or too small/unaligned for hugepage. */ > progress++; > continue; > }