From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 5035FEB7EB2 for ; Wed, 4 Mar 2026 09:22:53 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id A30F46B0089; Wed, 4 Mar 2026 04:22:52 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id A00F46B008A; Wed, 4 Mar 2026 04:22:52 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 93A936B008C; Wed, 4 Mar 2026 04:22:52 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0014.hostedemail.com [216.40.44.14]) by kanga.kvack.org (Postfix) with ESMTP id 7F3686B0089 for ; Wed, 4 Mar 2026 04:22:52 -0500 (EST) Received: from smtpin18.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay04.hostedemail.com (Postfix) with ESMTP id 308451A04DC for ; Wed, 4 Mar 2026 09:22:52 +0000 (UTC) X-FDA: 84507840984.18.682F1DC Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by imf02.hostedemail.com (Postfix) with ESMTP id 5EA9580003 for ; Wed, 4 Mar 2026 09:22:50 +0000 (UTC) Authentication-Results: imf02.hostedemail.com; dkim=none; spf=pass (imf02.hostedemail.com: domain of anshuman.khandual@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=anshuman.khandual@arm.com; dmarc=pass (policy=none) header.from=arm.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1772616170; h=from:from:sender: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=M+mHhI4gDc3H7z2Us0+E+GhRWYdqBuMRg81mbY1CCCk=; b=vSNeIi8nhzpG3eIWpDCk+QsqGVIA5T4mITj0w5EpH6DleK3mw77F2NP8lFH32gkIk0M76V hLkkq4wHzfcscNTkVqTZgO0S4+O77X3VltshwTKU4eN3D2qCVmog7G3E6kGtanegZlOqWT T24LeiCRtIaCyh4Kq7bdZMgpYTNns1k= ARC-Authentication-Results: i=1; imf02.hostedemail.com; dkim=none; spf=pass (imf02.hostedemail.com: domain of anshuman.khandual@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=anshuman.khandual@arm.com; dmarc=pass (policy=none) header.from=arm.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1772616170; a=rsa-sha256; cv=none; b=G2VnQdOCZdnSsdinwqwdKsMaB73I+sfC8yAgxcSnSz/QnSZT3N9E1WE5ZUlPd9ux56QN2q YzwgT3bA4XXdxXzXL7vaS678/p+mHaR/mSD1xj3LcVzacHCNXFk992dhWdNOE2gGPO7lk+ 6lKw7zVwY1aKGfsU/2TOXBHvwx0hHGs= 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 019F3339; Wed, 4 Mar 2026 01:22:43 -0800 (PST) Received: from [10.163.173.252] (unknown [10.163.173.252]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id EA8673F694; Wed, 4 Mar 2026 01:22:43 -0800 (PST) Message-ID: <346a421b-5b8e-41b7-b92e-a5a679030f1f@arm.com> Date: Wed, 4 Mar 2026 14:52:40 +0530 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] khugepaged: remove redundant index check for pmd-folios To: Dev Jain , akpm@linux-foundation.org, david@kernel.org, lorenzo.stoakes@oracle.com Cc: ziy@nvidia.com, baolin.wang@linux.alibaba.com, Liam.Howlett@oracle.com, npache@redhat.com, ryan.roberts@arm.com, baohua@kernel.org, lance.yang@linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20260227143501.1488110-1-dev.jain@arm.com> Content-Language: en-US From: Anshuman Khandual In-Reply-To: <20260227143501.1488110-1-dev.jain@arm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Stat-Signature: szjouemwoeu944p6tpbu1zk3c1pore4o X-Rspamd-Server: rspam09 X-Rspam-User: X-Rspamd-Queue-Id: 5EA9580003 X-HE-Tag: 1772616170-626881 X-HE-Meta: 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 jzIIkuGX JC+Tk9UXy5OhzpLzBqHrqVFWDASl78l3nK7viMafJ9FJ3VIJGPK+Sb7G6AMol5sR405CZ2pB4h3x1Yf4hddLBJFb6YUbmXCv/mh9fYOW2ReHeJMA4Xewxv6oZFWUt94fX+cpiZZuzD9AOI2+WQfYS52N/xiQnuBnlh5PPamAOR0LKJTdHYw9O3IvzETiA0EbFwFryWlZBijUqdsPc9E0F2fNeKJyflZuMoC3BPrsZaR57vlqCkdSbBYmOm7vr7Q2FHt/x Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 27/02/26 8:05 PM, Dev Jain wrote: > Claim: folio_order(folio) == HPAGE_PMD_ORDER => folio->index == start. > > Proof: Both loops in hpage_collapse_scan_file and collapse_file, which > iterate on the xarray, have the invariant that > start <= folio->index < start + HPAGE_PMD_NR ... (i) > > A folio is always naturally aligned in the pagecache, therefore > folio_order == HPAGE_PMD_ORDER => IS_ALIGNED(folio->index, HPAGE_PMD_NR) == true ... (ii) > > thp_vma_allowable_order -> thp_vma_suitable_order requires that the virtual > offsets in the VMA are aligned to the order, > => IS_ALIGNED(start, HPAGE_PMD_NR) == true ... (iii) > > Combining (i), (ii) and (iii), the claim is proven. > > Therefore, remove this check. > While at it, simplify the comments. > > Signed-off-by: Dev Jain Reviewed-by: Anshuman Khandual > --- > v1->v2: > - Remove the check instead of converting to VM_WARN_ON > - While at it, simplify the comments > > Based on mm-new (8982358e1c87). > > mm/khugepaged.c | 14 ++++---------- > 1 file changed, 4 insertions(+), 10 deletions(-) > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index 5f668c1dd0fe4..b7b4680d27ab1 100644 > --- a/mm/khugepaged.c > +++ b/mm/khugepaged.c > @@ -2015,9 +2015,7 @@ static enum scan_result collapse_file(struct mm_struct *mm, unsigned long addr, > * we locked the first folio, then a THP might be there already. > * This will be discovered on the first iteration. > */ > - if (folio_order(folio) == HPAGE_PMD_ORDER && > - folio->index == start) { > - /* Maybe PMD-mapped */ > + if (folio_order(folio) == HPAGE_PMD_ORDER) { > result = SCAN_PTE_MAPPED_HUGEPAGE; > goto out_unlock; > } > @@ -2345,15 +2343,11 @@ static enum scan_result hpage_collapse_scan_file(struct mm_struct *mm, > continue; > } > > - if (folio_order(folio) == HPAGE_PMD_ORDER && > - folio->index == start) { > - /* Maybe PMD-mapped */ > + if (folio_order(folio) == HPAGE_PMD_ORDER) { > result = SCAN_PTE_MAPPED_HUGEPAGE; > /* > - * For SCAN_PTE_MAPPED_HUGEPAGE, further processing > - * by the caller won't touch the page cache, and so > - * it's safe to skip LRU and refcount checks before > - * returning. > + * PMD-sized THP implies that we can only try > + * retracting the PTE table. > */ > folio_put(folio); > break;