From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; dkim=none Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id DF7D5DC; Wed, 29 Nov 2023 02:44:35 -0800 (PST) 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 BB5532F4; Wed, 29 Nov 2023 02:45:22 -0800 (PST) Received: from raptor (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 5B7453F5A1; Wed, 29 Nov 2023 02:44:30 -0800 (PST) Date: Wed, 29 Nov 2023 10:44:27 +0000 From: Alexandru Elisei To: David Hildenbrand 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, anshuman.khandual@arm.com, vincenzo.frascino@arm.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 v2 12/27] arm64: mte: Add tag storage pages to the MIGRATE_CMA migratetype Message-ID: References: <20231119165721.9849-1-alexandru.elisei@arm.com> <20231119165721.9849-13-alexandru.elisei@arm.com> <2aafd53f-af1f-45f3-a08c-d11962254315@redhat.com> Precedence: bulk X-Mailing-List: linux-fsdevel@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: <2aafd53f-af1f-45f3-a08c-d11962254315@redhat.com> Hi, On Tue, Nov 28, 2023 at 06:03:52PM +0100, David Hildenbrand wrote: > On 27.11.23 16:01, Alexandru Elisei wrote: > > Hi David, > > > > On Fri, Nov 24, 2023 at 08:40:55PM +0100, David Hildenbrand wrote: > > > On 19.11.23 17:57, Alexandru Elisei wrote: > > > > Add the MTE tag storage pages to the MIGRATE_CMA migratetype, which allows > > > > the page allocator to manage them like regular pages. > > > > > > > > Ths migratype lends the pages some very desirable properties: > > > > > > > > * They cannot be longterm pinned, meaning they will always be migratable. > > > > > > > > * The pages can be allocated explicitely by using their PFN (with > > > > alloc_contig_range()) when they are needed to store tags. > > > > > > > > Signed-off-by: Alexandru Elisei > > > > --- > > > > arch/arm64/Kconfig | 1 + > > > > arch/arm64/kernel/mte_tag_storage.c | 68 +++++++++++++++++++++++++++++ > > > > include/linux/mmzone.h | 5 +++ > > > > mm/internal.h | 3 -- > > > > 4 files changed, 74 insertions(+), 3 deletions(-) > > > > > > > > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig > > > > index fe8276fdc7a8..047487046e8f 100644 > > > > --- a/arch/arm64/Kconfig > > > > +++ b/arch/arm64/Kconfig > > > > @@ -2065,6 +2065,7 @@ config ARM64_MTE > > > > if ARM64_MTE > > > > config ARM64_MTE_TAG_STORAGE > > > > bool "Dynamic MTE tag storage management" > > > > + select CONFIG_CMA > > > > help > > > > Adds support for dynamic management of the memory used by the hardware > > > > for storing MTE tags. This memory, unlike normal memory, cannot be > > > > diff --git a/arch/arm64/kernel/mte_tag_storage.c b/arch/arm64/kernel/mte_tag_storage.c > > > > index fa6267ef8392..427f4f1909f3 100644 > > > > --- a/arch/arm64/kernel/mte_tag_storage.c > > > > +++ b/arch/arm64/kernel/mte_tag_storage.c > > > > @@ -5,10 +5,12 @@ > > > > * Copyright (C) 2023 ARM Ltd. > > > > */ > > > > +#include > > > > #include > > > > #include > > > > #include > > > > #include > > > > +#include > > > > #include > > > > #include > > > > #include > > > > @@ -189,6 +191,14 @@ static int __init fdt_init_tag_storage(unsigned long node, const char *uname, > > > > return ret; > > > > } > > > > + /* Pages are managed in pageblock_nr_pages chunks */ > > > > + if (!IS_ALIGNED(tag_range->start | range_len(tag_range), pageblock_nr_pages)) { > > > > + pr_err("Tag storage region 0x%llx-0x%llx not aligned to pageblock size 0x%llx", > > > > + PFN_PHYS(tag_range->start), PFN_PHYS(tag_range->end), > > > > + PFN_PHYS(pageblock_nr_pages)); > > > > + return -EINVAL; > > > > + } > > > > + > > > > ret = tag_storage_get_memory_node(node, &mem_node); > > > > if (ret) > > > > return ret; > > > > @@ -254,3 +264,61 @@ void __init mte_tag_storage_init(void) > > > > pr_info("MTE tag storage region management disabled"); > > > > } > > > > } > > > > + > > > > +static int __init mte_tag_storage_activate_regions(void) > > > > +{ > > > > + phys_addr_t dram_start, dram_end; > > > > + struct range *tag_range; > > > > + unsigned long pfn; > > > > + int i, ret; > > > > + > > > > + if (num_tag_regions == 0) > > > > + return 0; > > > > + > > > > + dram_start = memblock_start_of_DRAM(); > > > > + dram_end = memblock_end_of_DRAM(); > > > > + > > > > + for (i = 0; i < num_tag_regions; i++) { > > > > + tag_range = &tag_regions[i].tag_range; > > > > + /* > > > > + * Tag storage region was clipped by arm64_bootmem_init() > > > > + * enforcing addressing limits. > > > > + */ > > > > + if (PFN_PHYS(tag_range->start) < dram_start || > > > > + PFN_PHYS(tag_range->end) >= dram_end) { > > > > + pr_err("Tag storage region 0x%llx-0x%llx outside addressable memory", > > > > + PFN_PHYS(tag_range->start), PFN_PHYS(tag_range->end)); > > > > + ret = -EINVAL; > > > > + goto out_disabled; > > > > + } > > > > + } > > > > + > > > > + /* > > > > + * MTE disabled, tag storage pages can be used like any other pages. The > > > > + * only restriction is that the pages cannot be used by kexec because > > > > + * the memory remains marked as reserved in the memblock allocator. > > > > + */ > > > > + if (!system_supports_mte()) { > > > > + for (i = 0; i< num_tag_regions; i++) { > > > > + tag_range = &tag_regions[i].tag_range; > > > > + for (pfn = tag_range->start; pfn <= tag_range->end; pfn++) > > > > + free_reserved_page(pfn_to_page(pfn)); > > > > + } > > > > + ret = 0; > > > > + goto out_disabled; > > > > + } > > > > + > > > > + for (i = 0; i < num_tag_regions; i++) { > > > > + tag_range = &tag_regions[i].tag_range; > > > > + for (pfn = tag_range->start; pfn <= tag_range->end; pfn += pageblock_nr_pages) > > > > + init_cma_reserved_pageblock(pfn_to_page(pfn)); > > > > + totalcma_pages += range_len(tag_range); > > > > + } > > > > > > You shouldn't be doing that manually in arm code. Likely you want some cma.c > > > helper for something like that. > > > > If you referring to the last loop (the one that does > > ini_cma_reserved_pageblock()), indeed, there's already a function which > > does that, cma_init_reserved_areas() -> cma_activate_area(). > > > > > > > > But, can you elaborate on why you took this hacky (sorry) approach as > > > documented in the cover letter: > > > > No worries, it is indeed a bit hacky :) > > > > > > > > "The arm64 code manages this memory directly instead of using > > > cma_declare_contiguous/cma_alloc for performance reasons." > > > > > > What is the exact problem? > > > > I am referring to the performance degredation that is fixed in patch #26, > > "arm64: mte: Fast track reserving tag storage when the block is free" [1]. > > The issue is that alloc_contig_range() -> __alloc_contig_migrate_range() > > calls lru_cache_disable(), which IPIs all the CPUs in the system, and that > > leads to a 10-20% performance degradation on Chrome. It has been observed > > that most of the time the tag storage pages are free, and the > > lru_cache_disable() calls are unnecessary. > > This sounds like something eventually worth integrating into > CMA/alloc_contig_range(). Like, a fast path to check if we are only > allocating something small (e.g., falls within a single pageblock), and if > the page is free. > > > > > The performance degradation is almost entirely eliminated by having the code > > take the tag storage page directly from the free list if it's free, instead > > of calling alloc_contig_range(). > > > > Do you believe it would be better to use the cma code, and modify it to use > > this fast path to take the page drectly from the buddy allocator? > > That sounds reasonable yes. Do you see any blockers for that? I have been looking at the CMA code, and nothing stands out. I'll try changing the code to use cma_alloc/cma_release for the next iteration. > > > > > I can definitely try to integrate the code with cma_alloc(), but I think > > keeping the fast path for reserving tag storage is extremely desirable, > > since it makes such a huge difference to performance. > > Yes, but let's try finding a way to optimize common code, to eventually > improve some CMA cases as well? :) Sounds good, I'll try to integrate the fast path code to cma_alloc(), that way existing callers can benefit from it immediately. Thanks, Alex > > -- > Cheers, > > David / dhildenb >