From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-186.mta1.migadu.com (out-186.mta1.migadu.com [95.215.58.186]) (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 016C921257E for ; Mon, 1 Jun 2026 01:55:30 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.186 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780278932; cv=none; b=sRjfGCQJ+IJf0h+s69jgMoteNaLmWlg1odnccCuAmAfose7S/c9vQ/qME+E0uhTmeAbSc39fm5K6D3DhL2PoLbrDqp44TrkBfFHnZyioj9CcMNDLZWgV9fnAxunKpJeQGdA105G/gPl199wuN674uWVjr3oJXKSu/NtTvZ4EkeU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780278932; c=relaxed/simple; bh=j4uRY4vfme7Hj8zI1X26nZmyC//UW5FolYkUWvVXqhk=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=OAEXEyR8zeD7T0MfCGQzJwcuSYVl9BIGJkGsqzFVTTd1prnGjpsTMoi2P5PMkG+5RHY+qF123hlb7+NA7tlFwWq+HVL6V1LQl7Lvs+fjKKZCq89vCDsEfjAD0OMg1t+IxB5pZU7UnB51wxK6zWS8pslL/KbqFcJh5KfMslqo7rs= 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=GnCTJd3B; arc=none smtp.client-ip=95.215.58.186 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="GnCTJd3B" Message-ID: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1780278918; h=from:from: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=uQCbMRkdqdDT9GLUSMLXaeh0gg478vZBNxmXwoTOz6U=; b=GnCTJd3BSfUClP+EsrGgz2anJizI1lNps8XDR/4ezY3+8U5Tb14abeAfZv2bzXchAihLYN fo8bwJf0yz6X2MYCySFso5RSnCLFQzVrw/qGsL4jzIsdFzY9+5xj6RAlNCwd23SGSJ8xRa aMauQxDjTgID35xkiQSfsyXbn9R29L4= Date: Mon, 1 Jun 2026 09:53:28 +0800 Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH mm-unstable v18 12/14] mm/khugepaged: avoid unnecessary mTHP collapse attempts Content-Language: en-US To: "David Hildenbrand (Arm)" , npache@redhat.com Cc: 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, liam@infradead.org, ljs@kernel.org, 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, usama.arif@linux.dev References: <20260522150009.121603-13-npache@redhat.com> <20260531073102.20318-1-lance.yang@linux.dev> <65e201dd-10d6-43f6-8758-0fc313158fe7@kernel.org> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Lance Yang In-Reply-To: <65e201dd-10d6-43f6-8758-0fc313158fe7@kernel.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT On 2026/6/1 04:02, David Hildenbrand (Arm) wrote: > On 5/31/26 09:31, Lance Yang wrote: >> >> On Fri, May 22, 2026 at 09:00:07AM -0600, 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. >>> >>> Reviewed-by: Lorenzo Stoakes >>> Acked-by: Usama Arif >>> Acked-by: David Hildenbrand (Arm) >>> Signed-off-by: Nico Pache >>> --- >>> mm/khugepaged.c | 24 +++++++++++++++++++++++- >>> 1 file changed, 23 insertions(+), 1 deletion(-) >>> >>> diff --git a/mm/khugepaged.c b/mm/khugepaged.c >>> index d3d7db8be26c..15b7298bc225 100644 >>> --- a/mm/khugepaged.c >>> +++ b/mm/khugepaged.c >>> @@ -1535,9 +1535,31 @@ static int mthp_collapse(struct mm_struct *mm, struct vm_area_struct *vma, >>> collapse_address = address + offset * PAGE_SIZE; >>> ret = collapse_huge_page(mm, collapse_address, referenced, >>> unmapped, cc, order); >>> - if (ret == SCAN_SUCCEED) { >>> + >>> + switch (ret) { >>> + /* Cases where we continue to next collapse candidate */ >>> + case SCAN_SUCCEED: >>> collapsed += nr_ptes; >>> + fallthrough; >>> + case SCAN_PTE_MAPPED_HUGEPAGE: >>> continue; >>> + /* Cases where 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_NULL: >>> + case SCAN_DEL_PAGE_LRU: >>> + case SCAN_PTE_NON_PRESENT: >>> + case SCAN_PTE_UFFD_WP: >>> + case SCAN_ALLOC_HUGE_PAGE_FAIL: >> >> Nit: shouldn't SCAN_CGROUP_CHARGE_FAIL go with SCAN_ALLOC_HUGE_PAGE_FAIL >> here? >> >> If charging the current order fails, a smaller order might still fit :) > > I think the reasoning was here, that if we are already that close to our mem > limit, we should just give up instead of trying to squeeze it in .. :) Fair point. Just a nit, nevermind :)