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 5DBED379EF9 for ; Thu, 11 Jun 2026 06:49:36 +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=1781160586; cv=none; b=e6xJj3Z8CVBC8eSAHOZLj/7PE8i+KEGKK1xgyzW+zNV1D0QXsyURFe7BHsLC6TfqpI93M06QH06ua7rRLsTCJ5rAyuuwM20jNXUmtxZ/9lSqZ6CfOl6IoANSbV7vyJixRQhIOcNgretsHLhakCtkFZauS8rRuVQrkEnm/2NGE6s= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781160586; c=relaxed/simple; bh=s3juNGak86k3GfT3A59h76RswSCu5u3AoaI34WyvNIQ=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=DltRSNen1xCgn3pH2BzPJ985+XZ9vKyuYs70o68Ra42dGQWAwplY0ZlYBICA4UyH/6seR6QAJq5mtTycZeEoxvWoGWrzBbSWDP5grMV0ZvSTm/HA5ceAXuEnngRxhXC9WSzs6GRTmqt5HQ/1eHP1UHqFijxsxUPI9IxJfOSSeb4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Z6SKi/fi; 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="Z6SKi/fi" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3DA841F00893; Thu, 11 Jun 2026 06:49:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1781160575; bh=lC8ycInTVWa80ivQlmiFJsfkdHS3LZShZCSRnJHPAlA=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=Z6SKi/fiaA2C2wYajoTbWuUo44PjNAOAJTiPHw824PI9E6pXkIHtOqCt7sirQQmdh 6n2RHUP8v0VHzxMFhjmcUXxCXeLWeg3HED/QenMFuJBVdQUZEmSXodSDhbXbjJxaA9 Oz3cxcXVtSYJD5EIR1nsweD9YH1JlSEorvZD0QiXHnUcKyDTiTrvx7r9P8CL1n/d9z MSWLmlCyFlV1zXBx07Rf1aI652Yke4Gu3EhZ78CfM9cotPK/qjynEoF2P+k3bULQTF 7gqOsaS30CxIboAq+j7qM8/f+sqKLryS1gk8iaSLLOGohIllpuC+sVZo/9nvdTSKEj xOhsMuJp8cUQA== Date: Thu, 11 Jun 2026 09:49:22 +0300 From: Mike Rapoport To: Lance Yang Cc: dave.hansen@intel.com, xueyuan.chen21@gmail.com, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, x86@kernel.org, catalin.marinas@arm.com, will@kernel.org, tglx@kernel.org, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, luto@kernel.org, peterz@infradead.org, hpa@zytor.com, david@kernel.org, ljs@kernel.org, liam@infradead.org, vbabka@kernel.org, surenb@google.com, mhocko@suse.com, ziy@nvidia.com, baolin.wang@linux.alibaba.com, npache@redhat.com, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, yang@os.amperecomputing.com, jannh@google.com Subject: Re: [RFC PATCH v2 1/3] mm/huge_memory: make persistent huge zero folio read-only Message-ID: References: <930d9121-9176-4a7b-a2d7-8224f94000d3@intel.com> <20260610032022.23361-1-lance.yang@linux.dev> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260610032022.23361-1-lance.yang@linux.dev> Hi, On Wed, Jun 10, 2026 at 11:20:22AM +0800, Lance Yang wrote: > Hi Dave, > > Thanks for taking the time to review. > > On Tue, Jun 09, 2026 at 12:33:36PM -0700, Dave Hansen wrote: > >On 6/9/26 07:37, Xueyuan Chen wrote: > >> +bool __weak arch_make_pages_readonly(struct page *page, int nr_pages) > >> +{ > >> + return false; > >> +} > > > >This is a rather wonky function. It's going to cause all kinds of fun if > >it is used like this: > > > > arch_make_pages_readonly(syscall_table, 1); > > Ouch, yeah, it is ... We already have set_direct_map* APIs, why don't you add a new one there? set_direct_map_ro() for example. > >It's also kinda weird to have it return a bool, and not check that bool > >at the single call site. Some things come to mind: > > > >1. This function needs commenting. It needs to say what it does, when > > architectures should override it and what their implementations > > should look like. It needs to be clear that this can't be used for > > anything really important. What should architectures do with alias > > mappings? Are they allowed to touch non-direct map aliases? Are they > > required to? > > Agreed. Needs a real comment ... > > Just meant as a best-effort direct/linear-map permission chang, nothing > stronger than that. I should spell out what happens, or does not happen, > to non-direct-map aliases, if anything, and make clear callers cannot > treat this as a hard guarantee :D It's not only about highmem, anything that changes the direct map might fail to allocate memory when splitting larger mappings. > >2. The return type needs to be reconsidered. Is 'bool' even acceptable? > > Should it just be 'void' if callers can't do anything when it fails? > > Maybe ignoring it is OK now, but someone may need the return value later? > > >3. What should the naming be? "readonly" vs "ro". Should it have a > > "maybe" since it's kinda optional? > > Fair point. "make" may be overstating it a bit ... > > With a return value, arch_try_make_pages_readonly() sounds about right > to me. If we end up with void and pure best-effort semantics, maybe > arch_maybe_make_pages_readonly() fits better :) Realistically, I wouldn't expect 32-bit configs to enable PERSISTENT_HUGE_ZERO_FOLIO or even THP, so naming this function to reflect 32-bit behaviour seems odd going forward. > >4. Should this new API be folio or page-based in the first place? > > For page vs folio, I was mostly following David's RFC v1 suggestion. > > Current caller is a folio, sure, but the page-range helper leaves room > for non-folio users later. Happy to add a simple folio wrapper if that > reads better ;) > > >5. Is mm/huge_memory.c the right place to define a generic mm function, > > even a stub? > > Ah, you're right! My bad, wrong place for a generic stub. Will move it > out for RFC v3. We have include/linux/set_memory.h for such function declarations and their stubs. > Thanks, Lance > -- Sincerely yours, Mike.