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 198D9CD8CA8 for ; Wed, 10 Jun 2026 03:21:07 +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=ih1BA6VBQclIQnLMrdEp760CNzU2hkoYJjVIAwEnP8c=; b=MSWhuXcdBESMUE/011r9sKfbJm rMHZPSDhIfpIli9mH7r/iTBPwPJJ9+Asyb8amp9NCciexq6NkoWyA5codIyKTmMmS59RhvGJ+PqWk AhtiNwtv7SbpCSg5lsLuQEPR+ZceHXJxZgPabUA0KV7rUajYbANpNtefXJfRA0AVBeMNtNfjqdyaV fCmAqWVVY1UfyFErkPjfjUQH0X8gvD04gnHaEfxvsseatPWNRjtjuFYoFZgtcgAk4w44aG8wWzu4x ELMA1mbW3oR2FZqd46u//hSA3MzKU3QpRguC/wAJwRBdqA5h6WhdTYuQqtTITlwZv+Dv7bmqlztWo +XMZnX2A==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1wX9Ux-00000006jrW-46zD; Wed, 10 Jun 2026 03:20:59 +0000 Received: from out-181.mta0.migadu.com ([2001:41d0:1004:224b::b5]) by bombadil.infradead.org with esmtps (Exim 4.99.1 #2 (Red Hat Linux)) id 1wX9Uv-00000006jr4-1Akd for linux-arm-kernel@lists.infradead.org; Wed, 10 Jun 2026 03:20:58 +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=1781061643; 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=ih1BA6VBQclIQnLMrdEp760CNzU2hkoYJjVIAwEnP8c=; b=TnKTBVRJuvU106/Zwt6YCEBWfPJp5K1VWTaSFRqCyVV/HvjLO52x40h9PunBn/qPPEPU+n W5HpnKUtdMxNX2c0p1aagTgWS2XJRJssUy/LyBQ3F98/lV2TyDnX/q+L0kngAjjHEFSfW4 zLQyiio8VwGcbOAHXVj2V26/cY6XyGg= From: Lance Yang To: dave.hansen@intel.com Cc: 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, rppt@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, lance.yang@linux.dev, 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: Wed, 10 Jun 2026 11:20:22 +0800 Message-Id: <20260610032022.23361-1-lance.yang@linux.dev> In-Reply-To: <930d9121-9176-4a7b-a2d7-8224f94000d3@intel.com> References: <930d9121-9176-4a7b-a2d7-8224f94000d3@intel.com> 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-20260609_202057_476111_87324023 X-CRM114-Status: GOOD ( 18.87 ) 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 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 ... >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 >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 :) >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. Thanks, Lance