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 4BA093F8C7; Wed, 31 Jan 2024 06:24:30 +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=1706682273; cv=none; b=Ba5O+mAcerI/js1cdBQBIc27u3S9eRKCu+xfQKvLDI2/Xsdkh52zoSVrZxeVUKSps1q6kNzEMD1sYpzQi1w9Ipjc7Ym1WwvYswFK4eZZT+924uithDYjhm3LTFPe6wdRJ0ELjL2FPI9RwQDJB8LBv6TqCLIM8X34eDTqueEzCko= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1706682273; c=relaxed/simple; bh=Uiy2jl+TmsXsize8jHqdUqySPdi0wRe5XPyM63wYQ+A=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=MiJDIuHjX5w41KA+00TboYRpUhV8PKoetK0ZPIcf3iD0w24S+AR29uSE1pe66v4ae2lFddhNuHLwtIP/fO+xChI3UFY5jzAP4IW2L6Oijxq56gZW70WFZd5d4ZZ+cWmJlc8RE9uRqW32kB4XA+i/CWjNookkV6HcTBrDnKLv/KU= 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 C95BCDA7; Tue, 30 Jan 2024 22:25:13 -0800 (PST) Received: from [10.163.41.195] (unknown [10.163.41.195]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 307963F738; Tue, 30 Jan 2024 22:24:18 -0800 (PST) Message-ID: Date: Wed, 31 Jan 2024 11:54:17 +0530 Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH RFC v3 08/35] mm: cma: Introduce cma_alloc_range() Content-Language: en-US To: Alexandru Elisei 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 References: <20240125164256.4147-1-alexandru.elisei@arm.com> <20240125164256.4147-9-alexandru.elisei@arm.com> <61a3dbb7-25b6-4f49-aa70-9a8aaeb53365@arm.com> From: Anshuman Khandual In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit 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 ? > >> 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.