From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 85FD61C124F for ; Thu, 11 Apr 2024 15:37:58 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1712849879; cv=none; b=kdRI0GzvVZm4iDBTS9jTC+ADFMQ4PxaHGvghkxmYcfTSVttF1wVg+17sI5gv73JH7QYwfT1C0nYtnC8fZsBxudcENDAaF/CJEiLQjEMqFXkIyDE3AAFonp4WGraSzk9CVMqyYSN88pSfjojdend/JxvWtvyhnnUxyZLSoFjEkhc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1712849879; c=relaxed/simple; bh=MAMYui+jp1n4vPA6ZwebIUQNWsmP7XShJzR/yynCjEo=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=IgWte94ir1gGqZLXSlyK4iCeFkBaWXq/Fu7uB0aOSYbpKakFsVE6Wnp4Iw3OD7x3uTAV4XvLvaVnqOHtVlojzGH0VGlvCJD3jB2mWYgD/oc4YRrO5lAwfA3V77OAzTKkM1wulxhJwXYNtz8EYS9CubP01J6q2vYzasKVDe+S+Cg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 7EB48113E; Thu, 11 Apr 2024 08:38:27 -0700 (PDT) Received: from [10.1.38.151] (XHFQ2J9959.cambridge.arm.com [10.1.38.151]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id BBD303F6C4; Thu, 11 Apr 2024 08:37:56 -0700 (PDT) Message-ID: Date: Thu, 11 Apr 2024 16:37:55 +0100 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 v2 3/4] arm64: mm: Don't remap pgtables for allocate vs populate Content-Language: en-GB To: Mark Rutland Cc: Catalin Marinas , Will Deacon , Ard Biesheuvel , David Hildenbrand , Donald Dutile , Eric Chanudet , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Itaru Kitayama References: <20240404143308.2224141-1-ryan.roberts@arm.com> <20240404143308.2224141-4-ryan.roberts@arm.com> <37d4c278-3780-49ce-bd7e-e8f2ff4501fd@arm.com> From: Ryan Roberts In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 11/04/2024 16:25, Mark Rutland wrote: > On Thu, Apr 11, 2024 at 03:57:04PM +0100, Ryan Roberts wrote: >> On 11/04/2024 15:48, Mark Rutland wrote: >>> On Thu, Apr 11, 2024 at 02:37:49PM +0100, Ryan Roberts wrote: >>>> On 11/04/2024 14:02, Mark Rutland wrote: >>>>> but the logic remains fairly simple, and I suspect the overhead for late >>>>> allocations might not matter since the bulk of late changes are non-allocating. >>>> >>>> Its just the fixmap overhead that remains... >>> >>> True; my thinking there is that almost all of the later changes are for smaller >>> ranges than the linear map (~10s of MB vs GBs in your test data), so I'd expect >>> the overhead of those to be dominated by the cost of mappin the linear map. >>> >>> The only big exception is arch_add_memory(), but memory hotplug is incredibly >>> rare, and we're not making it massively slower than it already was... >> >> What about something like coco guest mem (or whatever its called). Isn't that >> scrubbed out of the linear map? So if a coco VM is started with GBs of memory, >> could that be a real case we want to optimize? > > I think that's already handled -- the functions we have to carve portions out > of the linear map use apply_to_page_range(), which doesn't use the fixmap. See > set_memory_*() and set_direct_map_*() in arch/arm64/mm/pageattr.c. Ahh gottya. Yet another table walker :) > > Note that apply_to_page_range() does what its name implies and *only* handles > mappings at page granularity. Hence not using that for > mark_linear_text_alias_ro() and mark_rodata_ro() which need to be able to > handle blocks. > > Mark.