From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-188.mta0.migadu.com (out-188.mta0.migadu.com [91.218.175.188]) (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 740C129DB9A for ; Wed, 10 Jun 2026 03:20:46 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.188 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781061647; cv=none; b=SY0KlLjLluE2Tq2WTU/rk7tBqSGCVjiVRcXx8HE17As1e7Ut32Vyg61umPio2sgWJ7E1suFSlwwq/XK2svmOcXKQ/lgo/BzEyv63A9fmOSs6JIvA9nEQ8tLDILj+cN/J7yQ8iughXWaXUxNSN0FQqr2Wggf6jTMIt3m+Ps0TjQo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781061647; c=relaxed/simple; bh=xhxG+5PMvZ1y9zbD64JhZpvp/xV02HrQoZ1lcu/5S5g=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version:Content-Type; b=kKaBRNho0fwhx1f5pKkZsP8j6XHYfhDcxRITPwDRykLVOa13uJXNGycb1LdF8O5H4pw/ZOeC0+45P2FqA2UMc8nX6zsXYazOgu30HUqdbCmzRyUgqDf5Iobb8MAWTfo2rGRy4e0+PImQcw6Onpt2jlUl8imTWER3E8J9zT5mbwE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=TnKTBVRJ; arc=none smtp.client-ip=91.218.175.188 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="TnKTBVRJ" 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> 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=UTF-8 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT 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