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imf18.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=LPoX9hoS; spf=pass (imf18.hostedemail.com: domain of david@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1780257742; a=rsa-sha256; cv=none; b=ZxZ9+iwz59/3H/FZ8d7J+Kd9CHRDwN7tnTpQgq/mtUTF/X99HLAo1zDZPpIl+u2KLgEUc2 WCqqzBQrWQeaEKSv3S3buQoDWPeg50/gt6CaDT/hNc4f0csqQP1SwJawPhuiksYDcTgikb 5IugcPNeu3QxQ+gmRziALirtVbVM/a8= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id A6414601FE; Sun, 31 May 2026 20:02:21 +0000 (UTC) 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 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 X-Stat-Signature: 497sqrh77xyrid3196zucumoy9bpqgee X-Rspam-User: X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 694D21C000E X-HE-Tag: 1780257742-220331 X-HE-Meta: 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 x/LGPR+x FVAxo3eI5rkaw4hGrb6+o7Husz2BDHuxMS2sMVgbS/5wiV4mZ9Zks0KuZkJPV88E3/aq8oauOcJ15uvYM96p6ixyYDtByoGSUXiAw5qjE8xH5d19r6cMA5sPh1q/eeeavBJxcBBJPWxhCa0YsPP3bO0y5GtjCVwqWNxlK7KGeMwKLBOgL5Y9jtwUoEIR3Vlp6TnkIlb9ZrJ01Ayw+VM4cWgl6NkIIKijt21kprrw3G7+CT1tuaZeid9uqRoRj+dK8hc5RlMgK4SIZxS0bE8mzQBtrPev2Xx2oFUjCfjc5S1iD2rObJVPs3P04ZZ8bd+uKRo38hylHbwMDp/Q= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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