From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 916834A35; Sun, 31 May 2026 20:02:21 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780257742; cv=none; b=QhGIUt9yPK8aHne6B2m01+AD0YR7b3G83MTUnhcenP2V7SKQU+ZAe6Q1e9HhHH9VTW0GMO8Rg8WsPDaEJzrifqhtJBy9ImTADhPRZf8as8X+0USLgW+un49iDiDdTuUuYIlIW6VkWkOxX4pxVmuxq6EfPnsQv7ckkoheqc/ivWc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780257742; c=relaxed/simple; bh=lNSGFc1py7VIGbjvLonHxt8pMByT2MfTGBn5QiYEtbA=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=vGQK/Lx/kcHzkmtRAn01a4cJmF1g8hvvLDxxHwK8MBLeU9e01Fo0OcUb2FAEunySyvb+4kNLL5D/8tgMed99kQLm/kFZ3KDV6Eb5/q0/AHE8Y6PEoJXN9DjmUqv4M7cvDGLggfPU2RZ1mtDtlhaSK1XBI+e/5s3SXpOMLiNjlxM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=LPoX9hoS; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="LPoX9hoS" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 02E301F00893; Sun, 31 May 2026 20:02:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1780257741; bh=T+kQsErqGbRV4q1yTjSudUgveQYxJiNOKFMvO3C/34w=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=LPoX9hoSuHAevhuAsdaNtw7K5pNs9DDP1Iv4g0ypR420Z4m+6X52d1pLhKSnlHAZj hsQBOfbXCXIlY7RGzxW72Yd5i8A5IYl01u3AQDe/TdXUwJkMmambVbpBYwC6KqgW4c MMBo9n+p8b3sr7q4XSyuMJHaexevO0WlycVCyyxAf8AQbpuhhtfh0QJwdRAMpM0CGl Ibo4DaSgoTPhRj7qGpF79Hi+ftM5Gmqk6X+V+pvbSQ0BtCTsNEy4RquvWwYdZhDBoI N8RWI14jMPca3RI6bdDCNgpwleqWHGFS8zTjH9vxQ8b4KzftsAuDvWkxkqmyIb1g6i 1N2+leEyRP8CQ== Message-ID: <65e201dd-10d6-43f6-8758-0fc313158fe7@kernel.org> Date: Sun, 31 May 2026 22:02:06 +0200 Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH mm-unstable v18 12/14] mm/khugepaged: avoid unnecessary mTHP collapse attempts To: Lance Yang , 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> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit 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 .. :) -- Cheers, David