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 8F68A109023F for ; Thu, 19 Mar 2026 15:59:10 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id D55076B0520; Thu, 19 Mar 2026 11:59:09 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id D2B586B0522; Thu, 19 Mar 2026 11:59:09 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id C413A6B0523; Thu, 19 Mar 2026 11:59:09 -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 B09296B0520 for ; Thu, 19 Mar 2026 11:59:09 -0400 (EDT) Received: from smtpin27.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay02.hostedemail.com (Postfix) with ESMTP id 6EF0113B2F2 for ; Thu, 19 Mar 2026 15:59:09 +0000 (UTC) X-FDA: 84563271618.27.8A21F83 Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf22.hostedemail.com (Postfix) with ESMTP id DB0E7C0005 for ; Thu, 19 Mar 2026 15:59:07 +0000 (UTC) Authentication-Results: imf22.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b="U/qOknp+"; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf22.hostedemail.com: domain of ljs@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=ljs@kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1773935947; 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: in-reply-to:in-reply-to:references:references:dkim-signature; bh=YzcOkDPq6Ist1fLDHgrMP5cByNJDD5WnbJutZsJi9mg=; b=1gU0Gg6Kvl/rc0q7IBb6B9OwvaMKvYvmUDu2LrBfD2qZvzS3ltXWPlF490r1OfL3i35IuJ 37PWGFPFrD46WicKyGY9IChiKqzjLCJOKWLOsDaOf/w2H5WWaV9PnAwNwVkKPkcVZ2dN72 s/hYaC1iwh4SdjejnxN7xWahunI2cug= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1773935947; a=rsa-sha256; cv=none; b=3PLtsUOL+JwEuD7qDLYQwz1wmBkVqNhnv1qgDzd2E/BEos9nukrSjzgyMs7bkg/H5uA/Tj ZjMSYaVpWbIf5WDA9BLfQ9qF7JVFT6U5oaEEfXy42YfzOac/LQXIPKcAL3IA19BqSuDn1d /wgDzu7WbGWKwRaIU4B+4wsiv7leeds= ARC-Authentication-Results: i=1; imf22.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b="U/qOknp+"; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf22.hostedemail.com: domain of ljs@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=ljs@kernel.org Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by tor.source.kernel.org (Postfix) with ESMTP id 317976013A; Thu, 19 Mar 2026 15:59:07 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4D16AC2BCAF; Thu, 19 Mar 2026 15:59:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1773935946; bh=Lb4oqU4iPyvZ1i8PhgXMxctkWzAoFzaDDuT6Xm9wAYc=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=U/qOknp+NF8zfgg9EcPZ92SUhgK1wewr6thkOtev0OirSgVgo8CxM22mhI9t4olCZ F9QKHOptUpnMSX4t//ajKhF5QZVTFfWiTzSdh88rgLDPci0Uy/5jKPaSIt/ZY+woCQ 1n1O3LjlaVjdze6GVVaNtuWOMomclWrAxCMWuiCtU/Xj6RODTMoR64DPCJ2wrJe3Lu 5XBLLtaNWFj+NSJ+SaQsQ1OkK6AmSV+CFKKwHIvC0xSPoR0rlXgaNxqOHEkmHJfDSu m0EFEZECCKyxoGkvSvJVq8deNghNUoIIkQ3zHPRhsF2x61w5GnxOB6q4xDOrVKDUW3 CYFk6ohEaWLnw== Date: Thu, 19 Mar 2026 15:59:04 +0000 From: "Lorenzo Stoakes (Oracle)" To: "David Hildenbrand (Arm)" Cc: Nico Pache , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-trace-kernel@vger.kernel.org, aarcange@redhat.com, akpm@linux-foundation.org, anshuman.khandual@arm.com, apopple@nvidia.com, baohua@kernel.org, baolin.wang@linux.alibaba.com, byungchul@sk.com, catalin.marinas@arm.com, cl@gentwo.org, corbet@lwn.net, dave.hansen@linux.intel.com, dev.jain@arm.com, gourry@gourry.net, hannes@cmpxchg.org, hughd@google.com, jack@suse.cz, jackmanb@google.com, jannh@google.com, jglisse@google.com, joshua.hahnjy@gmail.com, kas@kernel.org, lance.yang@linux.dev, Liam.Howlett@oracle.com, lorenzo.stoakes@oracle.com, mathieu.desnoyers@efficios.com, matthew.brost@intel.com, mhiramat@kernel.org, mhocko@suse.com, peterx@redhat.com, pfalcato@suse.de, rakie.kim@sk.com, raquini@redhat.com, rdunlap@infradead.org, richard.weiyang@gmail.com, rientjes@google.com, rostedt@goodmis.org, rppt@kernel.org, ryan.roberts@arm.com, shivankg@amd.com, sunnanyong@huawei.com, surenb@google.com, thomas.hellstrom@linux.intel.com, tiwai@suse.de, usamaarif642@gmail.com, vbabka@suse.cz, vishal.moola@gmail.com, wangkefeng.wang@huawei.com, will@kernel.org, willy@infradead.org, yang@os.amperecomputing.com, ying.huang@linux.alibaba.com, ziy@nvidia.com, zokeefe@google.com Subject: Re: [PATCH mm-unstable v15 11/13] mm/khugepaged: avoid unnecessary mTHP collapse attempts Message-ID: References: <20260226031741.230674-1-npache@redhat.com> <20260226032631.234234-1-npache@redhat.com> <4774da78-8349-4eda-a09b-7248e82cb26b@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4774da78-8349-4eda-a09b-7248e82cb26b@kernel.org> X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: DB0E7C0005 X-Stat-Signature: m6b449b6you3kcunnb5qokcbz3tjpymh X-Rspam-User: X-HE-Tag: 1773935947-835532 X-HE-Meta: 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 moUpdT8s opqHfw1Wk19wldm3xBYK+tVQf4ZPYTZr08xqMOt2DAf5osRZK1mUQIDnHi2bzUSzx/gUZX5YLvxT+wPsCvvhFINHnZExgzseAsIRQcvB60x1koas4GBAWlp5tZovkEZWl0nRI79djanM64g4ofnihaJBUK+9UJQC4NeAyXhckc3R7eJ/zAiF8oS0QlkLBz7/zOB9sMgwYHW/dxb+R1rJENqCEy1SiiigN5d0EpGE7HCFRrOX5MSuJCVEGNdMX+TwxWAUN8Jm+yOFBX7usk1uWl7g2tFn53ob1YIEUSDiKeZO8MfYCgvGrfffv7G1wEK1ZM+puXWHJ4o9IlZ8= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Mar 18, 2026 at 08:48:30PM +0100, David Hildenbrand (Arm) wrote: > On 3/18/26 19:59, Nico Pache wrote: > > > > > > On 3/17/26 4:35 AM, Lorenzo Stoakes (Oracle) wrote: > >> On Wed, Feb 25, 2026 at 08:26:31PM -0700, Nico Pache wrote: > >>> There are cases where, if an attempted collapse fails, all subsequent > >>> orders are guaranteed to also fail. Avoid these collapse attempts by > >>> bailing out early. > >>> > >>> Signed-off-by: Nico Pache > >> > >> With David's concern addressed: > >> > >> Reviewed-by: Lorenzo Stoakes (Oracle) > >> > >>> --- > >>> mm/khugepaged.c | 35 ++++++++++++++++++++++++++++++++++- > >>> 1 file changed, 34 insertions(+), 1 deletion(-) > >>> > >>> diff --git a/mm/khugepaged.c b/mm/khugepaged.c > >>> index 1c3711ed4513..388d3f2537e2 100644 > >>> --- a/mm/khugepaged.c > >>> +++ b/mm/khugepaged.c > >>> @@ -1492,9 +1492,42 @@ static int mthp_collapse(struct mm_struct *mm, unsigned long address, > >>> ret = collapse_huge_page(mm, collapse_address, referenced, > >>> unmapped, cc, mmap_locked, > >>> order); > >>> - if (ret == SCAN_SUCCEED) { > >>> + > >>> + switch (ret) { > >>> + /* Cases were we continue to next collapse candidate */ > >>> + case SCAN_SUCCEED: > >>> collapsed += nr_pte_entries; > >>> + fallthrough; > >>> + case SCAN_PTE_MAPPED_HUGEPAGE: > >>> continue; > >>> + /* Cases were lower orders might still succeed */ > >>> + case SCAN_LACK_REFERENCED_PAGE: > >>> + case SCAN_EXCEED_NONE_PTE: > >>> + case SCAN_EXCEED_SWAP_PTE: > >>> + case SCAN_EXCEED_SHARED_PTE: > >>> + case SCAN_PAGE_LOCK: > >>> + case SCAN_PAGE_COUNT: > >>> + case SCAN_PAGE_LRU: > >>> + case SCAN_PAGE_NULL: > >>> + case SCAN_DEL_PAGE_LRU: > >>> + case SCAN_PTE_NON_PRESENT: > >>> + case SCAN_PTE_UFFD_WP: > >>> + case SCAN_ALLOC_HUGE_PAGE_FAIL: > >>> + goto next_order; > >>> + /* Cases were no further collapse is possible */ > >>> + case SCAN_CGROUP_CHARGE_FAIL: > >>> + case SCAN_COPY_MC: > >>> + case SCAN_ADDRESS_RANGE: > >>> + case SCAN_NO_PTE_TABLE: > >>> + case SCAN_ANY_PROCESS: > >>> + case SCAN_VMA_NULL: > >>> + case SCAN_VMA_CHECK: > >>> + case SCAN_SCAN_ABORT: > >>> + case SCAN_PAGE_ANON: > >>> + case SCAN_PMD_MAPPED: > >>> + case SCAN_FAIL: > >>> + default: > >> > >> Agree with david, let's spell them out please :) > > > > I believe David is arguing for the opposite. To drop all these spelt out cases > > and just leave the default case. > > > > @david is that correct or did I misunderstand that. > > Either spell all out (no default) OR add a default. > > I prefer to just ... use the default :) I mean yup that's fine too I guess, all or nothing, something in between is weird! > > -- > Cheers, > > David Cheers, Lorenzo