From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 830E840DFAB; Thu, 12 Mar 2026 21:19:46 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773350386; cv=none; b=RiHUUubsXVzt8Kr10y0lLoT0p8bT/1zJJix8A4vR6IXIt+A+i4FqRrclcvEpUWx+Ul1eLFr0+6b0MHcY2UdSTGICdRmTy6f9Ls7N3voeuoaeUrk4n6hSt5p7YLo1RQPyCY3BMtuQkHbt8UVpUoJfjxEfYfnGqcnBe1e9+bIB+uI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773350386; c=relaxed/simple; bh=b/n1AB5/3Poo0rQsSnXTnJrEIrDJtXE5V+mRQh+spI4=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=UPbuqD9xKFxdvtv0zizcJT5fWfhmcXjMzJ1KWxMVp6+A3JQB+FvMq9zDGQiZa+BywPlYrR2YVMgP6HCsD6/9AQ/cvA0He1CQ+3lZsM7kb9sApLK9j9+Tl2Yt9rMn4Cvm9CerC6u417P4MoKdOagxAZvsvvlrtiJS6WgNm7a0IEQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=oAmgV2ar; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="oAmgV2ar" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3CE64C4CEF7; Thu, 12 Mar 2026 21:19:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1773350386; bh=b/n1AB5/3Poo0rQsSnXTnJrEIrDJtXE5V+mRQh+spI4=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=oAmgV2arw8JwtUgPzmUkQXEI7qwOzfCbG1n6XzBr808nXkT+OTjcRoZGUbQVs225r 9oL/+sG4BcrmV3hycYoRG47G00JbqB8hTMHM0ptNJU7mjsuefL4tvMRzuId6W14LfC IhC3XdsJFW4ICAXdSYDHW57MGspUq0ZIKv9UDCO2lWLUNOBuhtz5raqUE/EXj07yKw lSTutMzLLYbUh0c0Tgi5w3ADbIccOK0ATm2IM7ZQRhFJKmmxtB8JJh2aueu/1QEbET doHY7gQJmOOlG2DNwXemCr96moZ7CqMMX0kfhuAXOVJR/pnLfkaz6t22RHEZ5xmisP wmCkSME14rwIQ== Message-ID: Date: Thu, 12 Mar 2026 22:19:27 +0100 Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH mm-unstable v15 11/13] mm/khugepaged: avoid unnecessary mTHP collapse attempts To: Nico Pache , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-trace-kernel@vger.kernel.org Cc: 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 References: <20260226031741.230674-1-npache@redhat.com> <20260226032631.234234-1-npache@redhat.com> 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 2/26/26 04:26, 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: > + 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; > } > } > LGTM, but I do wonder, given that you have the "default" case, why spell out the ones that fall into the "default" category? I'd strip those /* For all other cases no futher collapse is possible */ default: return collapsed; Acked-by: David Hildenbrand (Arm) -- Cheers, David