From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-176.mta1.migadu.com (out-176.mta1.migadu.com [95.215.58.176]) (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 F1F05296BCB for ; Thu, 22 Jan 2026 08:44:45 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.176 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769071489; cv=none; b=juvkk3A8XU/8FwGGQmPfGQyyQI0Q2wyH8eJHIgIYbsxJqdWEGt1tA0cdVcucCpTGdJdkU5WuQ6oaqtMT8AWo5DPBteRjKicdGgS9HisyRuiEQk7YHoXUTW6/5jfzl3XNRz1Ak/E6sXny1AtFkqeE08CO5rDh0qmGWIWpsAB2NMo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769071489; c=relaxed/simple; bh=B5F81Th326xf7CAEQfq7ug0J0xtk8i0amunRHVBEIwQ=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=V2T6YLwPNdDG69SCks52wQ9xV8/qfjBFLzlM/DaZBvm072O4Eb3fYLheSEiMxwv+uS4xsIYfA1qPo0OqV4j5HBjPvO+jXxVOCXwDtyFqwkozxb9BsqQMHoEGOWkxfPOwQJvqijmVZPWuz/btw3yJak6zXMBVa5wbQwHXD2T13Qw= 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=xVxOOwda; arc=none smtp.client-ip=95.215.58.176 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="xVxOOwda" Message-ID: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1769071483; 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=LDpjBA56UpKXX0RpCliwDF6LnVmLT09CUYEpTS3IAnM=; b=xVxOOwda5jznK+jwyc6xIB0HOEPChs0qQ/1VykeGm/guAcD0Md7lhQkKBupy7FYG0W1ATK inN2d3OpwXCJKw0pf+YPIP6q+AK1pDQ5wdDTXZYFo5TrcsCmytsV+WupVyJEmAkVAlFsHt UvooVn43fq0gN1Tt/fn5gk7lEd0Jdb4= Date: Thu, 22 Jan 2026 16:44:31 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH V3 2/5] mm/khugepaged: count small VMAs towards scan limit Content-Language: en-US To: Dev Jain , Shivank Garg Cc: Zi Yan , Baolin Wang , "Liam R . Howlett" , Nico Pache , David Hildenbrand , Ryan Roberts , Barry Song , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Wei Yang , Lorenzo Stoakes , Andrew Morton References: <20260118192253.9263-4-shivankg@amd.com> <20260118192253.9263-8-shivankg@amd.com> <829b62c8-e3eb-485f-8d7b-01419c841cc8@arm.com> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Lance Yang In-Reply-To: <829b62c8-e3eb-485f-8d7b-01419c841cc8@arm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT On 2026/1/22 15:32, Dev Jain wrote: > > 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. Ah, you're right! I was worrying about a case that doesn't actually happen. Thanks, Lance > >> >> 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; >> }