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 7AD732EC0A4; Fri, 5 Jun 2026 18:07:18 +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=1780682839; cv=none; b=crqNNW3s7GAzfP9l6myBNUCfuQ3rZtQz20QfhnDz7lNfQw/U5NsPfe/bQvhniIbg9jfR0ygQcXdqUVobutvcTJwAo21EBel9BmV8hGT7r+nD8f3jsmg69TAuLtX/RPQFw6LisgSdGXAUVa8YhndmNh657hkT5QM8idWqoMzZfZ8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780682839; c=relaxed/simple; bh=xXq7HkR+vNYuMHeYJD9bWblvHRakO5bIzqxTfoE5zIA=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=YTmSC8ohN72JGzdwMMF9C+R+V3sfmsAcUD61YXNyZkhW3IsI0eYQ79vV0tknD77rwTtIUsAlpf2o9SwVWfEsunIXU7Gu6Hs2AMO22wQhqy2ULDOvKUA7WxxsSTMEIAlxPsSWOBhATewF4M20g/erlem1O4GVNBf/obX/wjoLerY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=alsX+KfK; 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="alsX+KfK" Received: by smtp.kernel.org (Postfix) with ESMTPSA id A07371F00893; Fri, 5 Jun 2026 18:07:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1780682838; bh=/Nhf4jMO4wZRRzTPNpV/mvbXK0GYYQL5VEX2HgG0GMc=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=alsX+KfKpBh3DHmOFR5AfpAGL8a8etxlfDAQgLlShE1jlMui4LaKD9+wiWQ42voDK 1xswb8uIL6om3S/gp1xwoeb6UEV8V6IWwkyfi/D9E9zDXUSCioSbKg2AHA+ZrY0BFE 2KZS4fs3fhWH8FIlfVJojSt6RX0bDEHEVF7OVAvL9h5+zR4sBRDLw10YjMYHjRWVgn LXwdC3Lvd34Oo6pG+yR6gf6mEfv/QDjo+K/VcfEBfifFGZZYnQsb2tocaaxiIlJQfy HTJTIbHVLR3z0JuQ/r1Hfi/yguSuZcybRH5O8fSD4DHd+AMDmED9H+IOjsNtAauyay 1dFEy9B6/ISyw== Message-ID: <177704e1-03b3-4791-9a69-9b83b72d61d5@kernel.org> Date: Fri, 5 Jun 2026 20:07:02 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH mm-unstable v19 00/14] khugepaged: add mTHP collapse support 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@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 References: <20260605161422.213817-1-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 6/5/26 18:14, Nico Pache wrote: > The following series provides khugepaged with the capability to collapse > anonymous memory regions to mTHPs. > > To achieve this we generalize the khugepaged functions to no longer depend > on PMD_ORDER. Then during the PMD scan, we use a bitmap to track individual > pages that are occupied (!none/zero). After the PMD scan is done, we use > the bitmap to find the optimal mTHP sizes for the PMD range. The > restriction on max_ptes_none is removed during the scan, to make sure we > account for the whole PMD range in the bitmap. When no mTHP size is > enabled, the legacy behavior of khugepaged is maintained. > > We currently only support max_ptes_none values of 0 or HPAGE_PMD_NR - 1 > (ie 511). If any other value is specified, the kernel will emit a warning > and mTHP collapse will default to max_ptes_none=0. If a mTHP collapse is > attempted, but contains swapped out, or shared pages, we don't perform > the collapse. > It is now also possible to collapse to mTHPs without requiring the PMD THP > size to be enabled. These limitations are to prevent collapse "creep" > behavior. This prevents constantly promoting mTHPs to the next available > size, which would occur because a collapse introduces more non-zero pages > that would satisfy the promotion condition on subsequent scans. > > Patch 1-2: Generalize hugepage_vma_revalidate and alloc_charge_folio > for arbitrary orders. > Patch 3: Rework max_ptes_* handling into helper functions > Patch 4: Generalize __collapse_huge_page_* for mTHP support > Patch 5: Require collapse_huge_page to enter/exit with the lock dropped > Patch 6: Generalize collapse_huge_page for mTHP collapse > Patch 7: Skip collapsing mTHP to smaller orders > Patch 8-9: Add per-order mTHP statistics and tracepoints > Patch 10: Introduce collapse_possible_orders helper functions > Patch 11-13: Introduce bitmap and mTHP collapse support, fully enabled > Patch 14: Documentation > Went through it and didn't find any blockers. Let's wait for Lorenzo's assessment. If he also doesn't find anything major, I think we can move forward with merging it and handle smaller things as follow-ups. -- Cheers, David