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[95.203.18.139]) by smtp.gmail.com with ESMTPSA id 2adb3069b0e04-59b7a0ca367sm3018309e87.38.2026.01.12.02.49.51 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 12 Jan 2026 02:49:52 -0800 (PST) From: Uladzislau Rezki X-Google-Original-From: Uladzislau Rezki Date: Mon, 12 Jan 2026 11:49:50 +0100 To: Dev Jain Cc: catalin.marinas@arm.com, will@kernel.org, urezki@gmail.com, akpm@linux-foundation.org, tytso@mit.edu, adilger.kernel@dilger.ca, cem@kernel.org, ryan.roberts@arm.com, anshuman.khandual@arm.com, shijie@os.amperecomputing.com, yang@os.amperecomputing.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, npiggin@gmail.com, willy@infradead.org, david@kernel.org, ziy@nvidia.com Subject: Re: [RESEND RFC PATCH 0/2] Enable vmalloc huge mappings by default on arm64 Message-ID: References: <20251212042701.71993-1-dev.jain@arm.com> Precedence: bulk X-Mailing-List: linux-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: <20251212042701.71993-1-dev.jain@arm.com> On Fri, Dec 12, 2025 at 09:56:59AM +0530, Dev Jain wrote: > In the quest for reducing TLB pressure via block mappings, enable huge > vmalloc by default on arm64 for BBML2-noabort systems which support kernel > live mapping split. > > This series is an RFC, because I cannot get a performance improvement for > the usual benchmarks which we have. Currently, vmalloc follows an opt-in > approach for block mappings - the users calling vmalloc_huge() are the ones > which expect the most advantage from block mappings. Most users of > vmalloc(), kvmalloc() and kvzalloc() map a single page. After applying this > series, it is expected that a considerable number of users will produce > cont mappings, and probably none will produce PMD mappings. > > I am asking for help from the community in testing - I believe that one of > the testing methods is xfstests: a lot of code uses the APIs mentioned > above. I am hoping that someone can jump in and run at least xfstests, and > probably some other tests which can take advantage of the reduced TLB > pressure from vmalloc cont mappings. > I checked how often vmalloc/vmap is triggered when i run xfstests. I think it also depends on env. and can be different from one setup to another. "echo vmalloc:alloc_vmap_area > set_event" urezki@milan:~/data/optane/xfs-test/xfstests.git$ wc -l ./vmalloc_traces/*.trace 2875 ./vmalloc_traces/generic_036.trace 30117 ./vmalloc_traces/generic_038.trace 8481 ./vmalloc_traces/generic_051.trace 16986 ./vmalloc_traces/generic_055.trace 6079 ./vmalloc_traces/generic_068.trace 2792 ./vmalloc_traces/generic_070.trace 26945 ./vmalloc_traces/generic_072.trace 2772 ./vmalloc_traces/generic_076.trace 2750 ./vmalloc_traces/generic_083.trace 3319 ./vmalloc_traces/generic_095.trace 2855 ./vmalloc_traces/generic_232.trace 3537 ./vmalloc_traces/generic_269.trace 21265 ./vmalloc_traces/generic_299.trace 3231 ./vmalloc_traces/generic_300.trace 3050 ./vmalloc_traces/generic_323.trace 2831 ./vmalloc_traces/generic_390.trace 4296 ./vmalloc_traces/generic_461.trace 4807 ./vmalloc_traces/generic_476.trace 3198 ./vmalloc_traces/generic_551.trace 3096 ./vmalloc_traces/generic_616.trace 6495 ./vmalloc_traces/generic_627.trace 11232 ./vmalloc_traces/generic_642.trace 11706 ./vmalloc_traces/generic_650.trace 3135 ./vmalloc_traces/generic_750.trace 5926 ./vmalloc_traces/generic_751.trace 77623 ./vmalloc_traces/xfs_013.trace 9172 ./vmalloc_traces/xfs_017.trace 4145 ./vmalloc_traces/xfs_068.trace 2982 ./vmalloc_traces/xfs_104.trace 7293 ./vmalloc_traces/xfs_167.trace 18851 ./vmalloc_traces/xfs_168.trace 4373 ./vmalloc_traces/xfs_442.trace 3550 ./vmalloc_traces/xfs_609.trace 321765 total urezki@milan:~/data/optane/xfs-test/xfstests.git$ Time execution is different for each test. For example "xfs_013" test takes around 200 seconds on my system and is in top of number of calls: 77623 / 200 = 388.115 calls/sec 200 / 77623 = 0.002576 = ~each 2.5ms Please note, i have not checked impact of your patch on time execution or how TLB pressure is affected. -- Uladzislau Rezki