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 0E92FFD8FCF for ; Thu, 26 Feb 2026 16:27:08 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 3063F6B0159; Thu, 26 Feb 2026 11:27:08 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 2B3066B015A; Thu, 26 Feb 2026 11:27:08 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 18B466B015B; Thu, 26 Feb 2026 11:27:08 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id 02F156B0159 for ; Thu, 26 Feb 2026 11:27:07 -0500 (EST) Received: from smtpin19.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay09.hostedemail.com (Postfix) with ESMTP id 9AB348AAB7 for ; Thu, 26 Feb 2026 16:27:07 +0000 (UTC) X-FDA: 84487137294.19.82E811C Received: from out-188.mta1.migadu.com (out-188.mta1.migadu.com [95.215.58.188]) by imf10.hostedemail.com (Postfix) with ESMTP id B45B1C0018 for ; Thu, 26 Feb 2026 16:27:05 +0000 (UTC) Authentication-Results: imf10.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=oYncBP7R; spf=pass (imf10.hostedemail.com: domain of usama.arif@linux.dev designates 95.215.58.188 as permitted sender) smtp.mailfrom=usama.arif@linux.dev; dmarc=pass (policy=none) header.from=linux.dev ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1772123226; 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-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=ZhpPpUmawavr8/7XO4FkbjGyfWyIYMOEPuIKrXPIOZ8=; b=HpNXfdVgWmmFUi1M+atI5ZKDetbTjsyfIhvOWcDEOxQxIPezKDcElPZ1R0miQ4x5YUhxci EJQFAsJ/UyX31L1rs1lZsJsbNkyqxKgCuNJ0I/zwjZq56gT4HTVIcq7KABF16ROS3f0snl 3VSdyC+rVAzrHBNSYoYfexRiHPHX0PI= ARC-Authentication-Results: i=1; imf10.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=oYncBP7R; spf=pass (imf10.hostedemail.com: domain of usama.arif@linux.dev designates 95.215.58.188 as permitted sender) smtp.mailfrom=usama.arif@linux.dev; dmarc=pass (policy=none) header.from=linux.dev ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1772123226; a=rsa-sha256; cv=none; b=tJDPAMbkigkmBHoHdy9tw2LkD18opZh54dXVbeIRnEPGnVndwLYOvQgCp1w5Zj8qyqpANa +E2c857bNtRnmpuB1PUbop7LVDonTIaJBfVM/W5WooCzbAZM1g9b3WgjsDJS0B0A+a3r12 7q0Q+5UEcGqnB9f3y4tf71KYUSuYju4= X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1772123222; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=ZhpPpUmawavr8/7XO4FkbjGyfWyIYMOEPuIKrXPIOZ8=; b=oYncBP7RaHS8J3MMylYArslXoH71eizg7mSGfgLGYgnJQMZRPlGt3Og7eMjJ3PDXcu0Cjf Iiuihwux6vl14q6/NYTTenfiDG7eC8xz67swamRfYHsVdoFeTWT3Bp41LT1gfO69H4ips3 QprD6BI2Yb6LF4d3T1CZMn9JbixT3Hc= From: Usama Arif To: Nico Pache Cc: Usama Arif , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-trace-kernel@vger.kernel.org, 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, david@kernel.org, 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 Date: Thu, 26 Feb 2026 08:26:52 -0800 Message-ID: <20260226162653.3802758-1-usama.arif@linux.dev> In-Reply-To: <20260226032631.234234-1-npache@redhat.com> References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Stat-Signature: rcttq3ybtcko7mewh5gocytufydmmiox X-Rspam-User: X-Rspamd-Queue-Id: B45B1C0018 X-Rspamd-Server: rspam02 X-HE-Tag: 1772123225-608464 X-HE-Meta: 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 IzptlGar 8DOUbzkChHL1BCd/hqcl/7W/z1ybpqW4Hnu07kT+ku/yYxcoQLMaoAb4lTIlfKNPHeS8HaxWLKtP3qt2SaBWTLHa7D6av27cgJo1ZWe2ppWQrZR8yYyn3uXSrOjoEKf8ZDHCoUzwneDUezFCx0F2kP1CZJmcTPsQyKMVghEer5uIliWFjjfseb/AyFZ/kFv5WCXMmx6Icejkfx7CSFNol2YPMPjmb6R8cBGGOoDEjWrD561s9vmWqq5x8gK22wtPjiRXLLJJLDUdWbzudkhpVcoqgCCOX4d8XcCAF Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, 25 Feb 2026 20:26:31 -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 > --- > 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: The only one that stands out to me is SCAN_CGROUP_CHARGE_FAIL. memcg charging of higher order folio might fail, but a lower order folio might pass? That said, if the cgroup is that tight, continuing collapse work may not be productive. Acked-by: Usama Arif > + 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: > + return collapsed; > } > } > > -- > 2.53.0 > >