From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-188.mta1.migadu.com (out-188.mta1.migadu.com [95.215.58.188]) (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 7C04F43D510 for ; Thu, 26 Feb 2026 16:27:05 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.188 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772123227; cv=none; b=hZ5CKMtvwLovvpc9VX1kHMc0ppBp5L84THO+llIwrWPw7zdup2fMHpvu58l+/XJPCwVZLx2f7k9gH0jR6kNErTRzhFDS+goek9wZPChOTlwfQxzxW8oraCfyrs6KdjleqO90ksKY7Qx6rfNodDAl6vzeqWVYWySfhkCymokq3GQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772123227; c=relaxed/simple; bh=HKqtr3coDZJQB8tfZLk/fEJRSL3Be6NnnvgjgP9uZHU=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=WNmQ4WThUEUaYH/uaFUrDXPu7Zb9Ark/7I4Stzk4GKnDXAFI10aexnb9Efbv+KzQzDXimDLvwHtttZLOLxuMC3fCXHCG6jEl+7bgf117LTttFWJt+jfGfJC2xz6e6tmdLkTt1oAI0LQiXtCKZjE404oAHTw8y0NBPQx0mOHnwUQ= 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=oYncBP7R; arc=none smtp.client-ip=95.215.58.188 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="oYncBP7R" 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: Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT 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 > >