From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 80B75CD98D2 for ; Thu, 11 Jun 2026 10:36:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: Content-Type:MIME-Version:References:In-Reply-To:Message-Id:Date:Subject:Cc: To:From:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=JcsQscn35Hn+B3P9DzOAGAp7XTk6vMF6bXs5BZWRQI4=; b=wQUsIVI8D2d0vtkxRgsSnSXHVE yB+nHnP3fOQYt+Z0oy/M8DqHy2qfYUX7X4vLUWbQUWKulUsWr/hMUSdAkY/ir8l1h1RiFI/XEZD2H K2qScw8UFC1SaUfdvte/6qTTWpph0mSRWpjUxOaI66fUWROf5KzPRnbf/6cihjBLGXWl7EnfPJJDZ oA6m/iFL7AnqMbg1xMicAJi20OhYc50Pez3bLTcqcp6caXcTy31DJOQcXPiMLdEAntjQWLvkHKIFq RLdO+YhLXwg7KOegIvCIt5N09FnuYK6qJWGVOe5RmWmqRsRjFufQpvG1LF9soSRuAZEy5QvJ+czXD YigEz1aw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1wXclc-00000009Emw-3D0r; Thu, 11 Jun 2026 10:36:08 +0000 Received: from out-176.mta1.migadu.com ([2001:41d0:203:375::b0]) by bombadil.infradead.org with esmtps (Exim 4.99.1 #2 (Red Hat Linux)) id 1wXcla-00000009ElZ-0hN3 for linux-arm-kernel@lists.infradead.org; Thu, 11 Jun 2026 10:36:07 +0000 X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1781174139; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=JcsQscn35Hn+B3P9DzOAGAp7XTk6vMF6bXs5BZWRQI4=; b=KFy8/n/U/fMnO10jGMsAygH4UuAAi21IOhBjFo7Xzu7zVu4XCvEjkoJ8LarfwYpOklSdRa kWeT9p74fCYbUZZMIJscQ118mwSlcgHEyJ71iwi/tBAUUtGcxMEmP6dGbNqb+yMd49Y/LP 6NH3XiQ/KrwvwidiAoww7440ILnsNRI= From: Lance Yang To: rppt@kernel.org Cc: lance.yang@linux.dev, 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 Date: Thu, 11 Jun 2026 18:35:12 +0800 Message-Id: <20260611103512.46955-1-lance.yang@linux.dev> In-Reply-To: References: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260611_033606_360272_5E2B1C3B X-CRM114-Status: GOOD ( 26.50 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Thu, Jun 11, 2026 at 09:49:22AM +0300, Mike Rapoport wrote: >Hi, 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. Good point. I was trying to make this generic, but that's a bit too cute. This is really a direct-map thing, so adding a set_direct_map_ro() helper there makes more sense. > >> >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. Yes, exactly. > >> >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. Cool with that, if no one objects. No need to bake that into the name I guess. int return plus a comment should be enough, just like set_direct_map_*() family already does :) >> >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. Yep, will move it there :) Thanks, Lance