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 CF1035F54E; Tue, 13 Feb 2024 17:26:34 +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=1707845197; cv=none; b=R1bYXXkVa4eSjI5bzrWNcIqyHTGQ7e5foFalkIsNMZLrsAbs1RpzkqLm2DcpwV3EbmMTRUQIIbK4tp+kFybwcvXJ+GDnNJHlbG3QjLbafVbjNFjtfzmxqnK6W/kt+dkTy4hYGkHi2Dx0Zs1o1BF8Y/RZHBhl8U7j6M5PmDwuNMA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1707845197; c=relaxed/simple; bh=R4W/x6sdikq9L5mixsfBJrQlDgWaZ0hlbKehGewQpgE=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=Bpv+ETvxc3uxOp4XmDz1Cw1ZpprtDQkn21HxeeumLOTto2Pwqc4ZcK9AdTuuAt1RoKaCGiTYqnsIVqcm1sTphAFRNZOgFzk8+0q3Tp/T7m2zYuNFIB+FzecHVP5kv7kvriGoBM9WcbuUF/jrm+6O2B42GsQCL+MpSZroLNydico= 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 724E71FB; Tue, 13 Feb 2024 09:27:15 -0800 (PST) Received: from [10.1.196.40] (e121345-lin.cambridge.arm.com [10.1.196.40]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 155943F5A1; Tue, 13 Feb 2024 09:26:27 -0800 (PST) Message-ID: Date: Tue, 13 Feb 2024 17:26:26 +0000 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 v4 01/10] iommu/vt-d: add wrapper functions for page allocations Content-Language: en-GB To: Pasha Tatashin Cc: akpm@linux-foundation.org, alim.akhtar@samsung.com, alyssa@rosenzweig.io, asahi@lists.linux.dev, baolu.lu@linux.intel.com, bhelgaas@google.com, cgroups@vger.kernel.org, corbet@lwn.net, david@redhat.com, dwmw2@infradead.org, hannes@cmpxchg.org, heiko@sntech.de, iommu@lists.linux.dev, jernej.skrabec@gmail.com, jonathanh@nvidia.com, joro@8bytes.org, krzysztof.kozlowski@linaro.org, linux-doc@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-rockchip@lists.infradead.org, linux-samsung-soc@vger.kernel.org, linux-sunxi@lists.linux.dev, linux-tegra@vger.kernel.org, lizefan.x@bytedance.com, marcan@marcan.st, mhiramat@kernel.org, m.szyprowski@samsung.com, paulmck@kernel.org, rdunlap@infradead.org, samuel@sholland.org, suravee.suthikulpanit@amd.com, sven@svenpeter.dev, thierry.reding@gmail.com, tj@kernel.org, tomas.mudrunka@gmail.com, vdumpa@nvidia.com, wens@csie.org, will@kernel.org, yu-cheng.yu@intel.com, rientjes@google.com, bagasdotme@gmail.com, mkoutny@suse.com References: <20240207174102.1486130-1-pasha.tatashin@soleen.com> <20240207174102.1486130-2-pasha.tatashin@soleen.com> <8ce2cd7b-7702-45aa-b4c8-25a01c27ed83@arm.com> From: Robin Murphy In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 10/02/2024 2:21 am, Pasha Tatashin wrote: [...] >>> +/** >>> + * iommu_alloc_pages_node - allocate a zeroed page of a given order from >>> + * specific NUMA node. >>> + * @nid: memory NUMA node id >>> + * @gfp: buddy allocator flags >>> + * @order: page order >>> + * >>> + * returns the virtual address of the allocated page >>> + */ >>> +static inline void *iommu_alloc_pages_node(int nid, gfp_t gfp, int order) >>> +{ >>> + struct page *page = __iommu_alloc_pages_node(nid, gfp, order); >>> + >>> + if (unlikely(!page)) >>> + return NULL; >> >> As a general point I'd prefer to fold these checks into the accounting >> function itself rather than repeat them all over. > > For the free functions this saves a few cycles by not repeating this > check again inside __free_pages(), to keep things symmetrical it makes > sense to keep __iomu_free_account and __iomu_alloc_account the same. > With the other clean-up there are not that many of these checks left. __free_pages() doesn't accept NULL, so __iommu_free_pages() shouldn't need a check; free_pages() does, but correspondingly iommu_free_pages() needs its own check up-front to avoid virt_to_page(NULL); either way it means there are no callers of iommu_free_account() who should be passing NULL. The VA-returning allocators of course need to avoid page_address(NULL), so I clearly made this comment in the wrong place to begin with, oops. In the end I guess that will leave __iommu_alloc_pages() as the only caller of iommu_alloc_account() who doesn't already need to handle their own NULL. OK, I'm convinced, apologies for having to bounce it off you to work it through :) >>> + */ >>> +static inline void *iommu_alloc_page_node(int nid, gfp_t gfp) >>> +{ >>> + return iommu_alloc_pages_node(nid, gfp, 0); >>> +} >> >> TBH I'm not entirely convinced that saving 4 characters per invocation >> times 11 invocations makes this wrapper worthwhile :/ > > Let's keep them. After the clean-up that you suggested, there are > fewer functions left in this file, but I think that it is cleaner to > keep these remaining, as it is beneficial to easily distinguish when > exactly one page is allocated vs when multiple are allocated via code > search. But is it, really? It's not at all obvious to me *why* it would be significantly interesting to distinguish fixed order-0 allocations from higher-order or variable-order (which may still be 0) ones. After all, there's no regular alloc_page_node() wrapper, yet plenty more callers of alloc_pages_node(..., 0) :/ Thanks, Robin.