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 CF2E169D00; Wed, 31 Jan 2024 14:18:34 +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=1706710716; cv=none; b=pb/+9QLaFReQoYWx8O2GvCDGsIiSiISnMAW3wjKxNauHAJeF9sBgGtiaF+GCYyIr3F1z7THKs1m+fAaW4RxH9VzV6Y2UPQKuIJT/DTXLq8Di+7v63fTLF3hf+agks00VY90YEkm96O7qcbOtZVxRMT/J10MUtgX/44Xl9OVriis= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1706710716; c=relaxed/simple; bh=2efCmHXOKMA9e2vGpnP2bHu385K2t0wVYZiGw3jyuHQ=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=ULuSKeLUO4acVcmnU/zKCBZ+JBBiEei3+Gp1/9tYHHO4wb5UsIKuochhoEmm9FExWTT8TESGxqZisEwnvKrRaAV/xbdWjaLm5xOUCE7A1nKSf2XhCrOlhscosStpqJXFJTbge3sJqItNlqbISoVCgT/Fi+cKwPrfr05l1CHAqHE= 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 5F9F4DA7; Wed, 31 Jan 2024 06:19:17 -0800 (PST) Received: from raptor (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 150DA3F738; Wed, 31 Jan 2024 06:18:28 -0800 (PST) Date: Wed, 31 Jan 2024 14:18:22 +0000 From: Alexandru Elisei To: Anshuman Khandual Cc: catalin.marinas@arm.com, will@kernel.org, oliver.upton@linux.dev, maz@kernel.org, james.morse@arm.com, suzuki.poulose@arm.com, yuzenghui@huawei.com, arnd@arndb.de, akpm@linux-foundation.org, mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, bristot@redhat.com, vschneid@redhat.com, mhiramat@kernel.org, rppt@kernel.org, hughd@google.com, pcc@google.com, steven.price@arm.com, vincenzo.frascino@arm.com, david@redhat.com, eugenis@google.com, kcc@google.com, hyesoo.yu@samsung.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, kvmarm@lists.linux.dev, linux-fsdevel@vger.kernel.org, linux-arch@vger.kernel.org, linux-mm@kvack.org, linux-trace-kernel@vger.kernel.org Subject: Re: [PATCH RFC v3 08/35] mm: cma: Introduce cma_alloc_range() Message-ID: References: <20240125164256.4147-1-alexandru.elisei@arm.com> <20240125164256.4147-9-alexandru.elisei@arm.com> <61a3dbb7-25b6-4f49-aa70-9a8aaeb53365@arm.com> Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Hi, On Wed, Jan 31, 2024 at 11:54:17AM +0530, Anshuman Khandual wrote: > > > On 1/30/24 17:05, Alexandru Elisei wrote: > > Hi, > > > > On Tue, Jan 30, 2024 at 10:50:00AM +0530, Anshuman Khandual wrote: > >> > >> On 1/25/24 22:12, Alexandru Elisei wrote: > >>> Today, cma_alloc() is used to allocate a contiguous memory region. The > >>> function allows the caller to specify the number of pages to allocate, but > >>> not the starting address. cma_alloc() will walk over the entire CMA region > >>> trying to allocate the first available range of the specified size. > >>> > >>> Introduce cma_alloc_range(), which makes CMA more versatile by allowing the > >>> caller to specify a particular range in the CMA region, defined by the > >>> start pfn and the size. > >>> > >>> arm64 will make use of this function when tag storage management will be > >>> implemented: cma_alloc_range() will be used to reserve the tag storage > >>> associated with a tagged page. > >> Basically, you would like to pass on a preferred start address and the > >> allocation could just fail if a contig range is not available from such > >> a starting address ? > >> > >> Then why not just change cma_alloc() to take a new argument 'start_pfn'. > >> Why create a new but almost similar allocator ? > > I tried doing that, and I gave up because: > > > > - It made cma_alloc() even more complex and hard to follow. > > > > - What value should 'start_pfn' be to tell cma_alloc() that it should be > > ignored? Or, to put it another way, what pfn number is invalid on **all** > > platforms that Linux supports? > > > > I can give it another go if we can come up with an invalid value for > > 'start_pfn'. > > Something negative might work. How about -1/-1UL ? A quick search gives > some instances such as ... > > git grep "pfn == -1" > > mm/mm_init.c: if (*start_pfn == -1UL) > mm/vmscan.c: if (pfn == -1) > mm/vmscan.c: if (pfn == -1) > mm/vmscan.c: if (pfn == -1) > tools/testing/selftests/mm/hugepage-vmemmap.c: if (pfn == -1UL) { > > Could not -1UL be abstracted as common macro MM_INVALID_PFN to be used in > such scenarios including here ? Ah yes, you are right, get_pte_pfn() already uses -1 as an invalid pfn, so I can just use that. Will definitely give it a go on the next iteration, thanks for the suggestion! > > > > >> But then I am wondering why this could not be done in the arm64 platform > >> code itself operating on a CMA area reserved just for tag storage. Unless > >> this new allocator has other usage beyond MTE, this could be implemented > >> in the platform itself. > > I had the same idea in the previous iteration, David Hildenbrand suggested > > this approach [1]. > > > > [1] https://lore.kernel.org/linux-fsdevel/2aafd53f-af1f-45f3-a08c-d11962254315@redhat.com/ > > There are two different cma_alloc() proposals here - including the next > patch i.e mm: cma: Fast track allocating memory when the pages are free > > 1) Augment cma_alloc() or add cma_alloc_range() with start_pfn parameter > 2) Speed up cma_alloc() for small allocation requests when pages are free > > The second one if separated out from this series could be considered on > its own as it will help all existing cma_alloc() callers. The first one > definitely needs an use case as provided in this series. I understand, thanks for the input! Alex