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 07226CD3424 for ; Wed, 6 May 2026 06:46:53 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 317CA6B0005; Wed, 6 May 2026 02:46:53 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 2C8CC6B0088; Wed, 6 May 2026 02:46:53 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 1DEC16B008A; Wed, 6 May 2026 02:46:53 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0010.hostedemail.com [216.40.44.10]) by kanga.kvack.org (Postfix) with ESMTP id 094F16B0005 for ; Wed, 6 May 2026 02:46:53 -0400 (EDT) Received: from smtpin23.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay03.hostedemail.com (Postfix) with ESMTP id A2483A04BE for ; Wed, 6 May 2026 06:46:52 +0000 (UTC) X-FDA: 84736062264.23.87EC710 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by imf14.hostedemail.com (Postfix) with ESMTP id 7CC43100003 for ; Wed, 6 May 2026 06:46:50 +0000 (UTC) Authentication-Results: imf14.hostedemail.com; dkim=pass header.d=arm.com header.s=foss header.b=iZSjygop; spf=pass (imf14.hostedemail.com: domain of dev.jain@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=dev.jain@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=1778050011; 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:dkim-signature; bh=fDIKOXzLh8b/6k4kDMKE5XN9tNAAyDfy7kHAa6y+dGs=; b=Be/0SOXFzu2RMg/FHc+Lmr5luMt2pFLgKClRYnR8k/r5ugHu+RRGKZ64mgdC+hCKGzIm9c p+65RhdmX9SEfeM5UP1UNAczR9GWsFm/QsUJtzhPbKz6wRxAJiohqLuovJixO7pfEN/XCf kMb/cmNN/C1par0Wa+7YLrkFuGn+fX4= ARC-Authentication-Results: i=1; imf14.hostedemail.com; dkim=pass header.d=arm.com header.s=foss header.b=iZSjygop; spf=pass (imf14.hostedemail.com: domain of dev.jain@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=dev.jain@arm.com; dmarc=pass (policy=none) header.from=arm.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1778050011; a=rsa-sha256; cv=none; b=UEmv+rV66sbBe+0SoZ8Yb6t+UrRmBEoUEKhowMgYCLkXhb/in2UUjyD6vQgn102oNzX0BS CiX5igN9ybVl05KmtBJU+Pm3tWBJMpY7A2HuJA/z7/i+eVwBLH5gu8ya5DAAyW2nr6F6Ns g/o00iXYaG3tW68WRYuxrwTKFCEYoqQ= 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 164071A25; Tue, 5 May 2026 23:46:44 -0700 (PDT) Received: from [10.164.148.46] (MacBook-Pro.blr.arm.com [10.164.148.46]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 0139E3F763; Tue, 5 May 2026 23:46:44 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1778050009; bh=HFZLpvkdsNmTj63qRZ7hFn86ZsvIp71KRJEco/ZEoww=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=iZSjygopO7FKtdzR7WuyKQRo4UxpS+t/O4U4GQ4lSfoaQtPS/qNgUJKQAO0o5JqEO XhZxOFlIBLwPAN1Cmf6hP+b6FbHcGABYauA6SLw62LqPzySqOIM4mQ4aMWLek12rxk rGiRJXuxCEbQc3MFkLnNvPba33PW5CQK0YQKnOok= Message-ID: <3fb8c00d-d60d-4fec-81b1-e7633384a52d@arm.com> Date: Wed, 6 May 2026 12:16:35 +0530 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] mm/khugepaged: clear MMF_VM_HUGEPAGE on mm_slot_alloc() failure To: Ye Liu , Andrew Morton , David Hildenbrand , Lorenzo Stoakes , Xin Hao Cc: Ye Liu , Zi Yan , Baolin Wang , "Liam R. Howlett" , Nico Pache , Ryan Roberts , Barry Song , Lance Yang , Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20260506012130.9306-1-ye.liu@linux.dev> Content-Language: en-US From: Dev Jain In-Reply-To: <20260506012130.9306-1-ye.liu@linux.dev> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 7CC43100003 X-Rspam-User: X-Stat-Signature: cz6th1gehsxwie9etcmt3b3g9pgp1iyf X-HE-Tag: 1778050010-628170 X-HE-Meta: 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 hbxid9Md Pwai3cTEmgsn7U4hblc3jY1iwWQ5EDZqVfBSppxSR/ofPzdOFljYlMhOOGWKyGXzi5ZnL1V1cUyPEokd6zL2NauMp/rc+RHQzfrH6K34oiPSIcNHhIk9p3y8kIJMYcp5xQhfrAPEKYm349zfC32IHr+UdbSY/RoBgZ6LwybbpDBNM8wGSpw3iZ7X4tlpb/buSDsH6LUlvwlzCm6VbHEuJFMBYEJV2w59dWkhBkjysCdEFt7rkoIiAJmXBWD1aQApYhMjviraKcw27EdJIRB3hpAKtSeJcevp26H0MNEfEg1RV6SdjwEjtSok8PhvbFyMYTA9jL0yejNvkmDvDCjNtg9vJhA== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 06/05/26 6:51 am, Ye Liu wrote: > From: Ye Liu > > __khugepaged_enter() sets MMF_VM_HUGEPAGE before allocating the > corresponding mm_slot. If mm_slot_alloc() fails, the function > returns with the flag set but without inserting the mm into the > khugepaged tracking structures. > > This leaves the mm in an inconsistent state: it is marked as > registered (MMF_VM_HUGEPAGE set), but will never be scanned by > khugepaged. Future attempts to register the mm are skipped since > khugepaged_enter_vma() checks the flag and returns early. > > Fix this by clearing MMF_VM_HUGEPAGE when mm_slot_alloc() fails, > restoring the ability to retry registration later. > > Fixes: 16618670276a ("mm: khugepaged: avoid pointless allocation for struct mm_slot") > Signed-off-by: Ye Liu > --- > Changes since v1: > - Add Fixes tag as suggested by Dev Jain and Lance Yang > > mm/khugepaged.c | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index 7d48d4fbd5f3..60ab7c1b61dd 100644 > --- a/mm/khugepaged.c > +++ b/mm/khugepaged.c > @@ -559,8 +559,10 @@ void __khugepaged_enter(struct mm_struct *mm) > return; > > slot = mm_slot_alloc(mm_slot_cache); > - if (!slot) > + if (!slot) { > + mm_flags_clear(MMF_VM_HUGEPAGE, mm); > return; > + } Note that, a racing khugepaged_enter_vma() may back off when it sees that MMF_VM_HUGEPAGE is set, but then the above clears the flag after slot alloc failure. So we end up not registering the mm with khugepaged. But I am sure no one cares, we are in much big trouble if slot alloc is failing. Although one could argue the same about this patch, I will still say it is important to fix "flag is set but not registered with khugepaged" because that just feels wrong. Reviewed-by: Dev Jain > > spin_lock(&khugepaged_mm_lock); > mm_slot_insert(mm_slots_hash, mm, slot);