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Thu, 16 Oct 2025 09:12:38 -0700 (PDT) From: Uladzislau Rezki X-Google-Original-From: Uladzislau Rezki Date: Thu, 16 Oct 2025 18:12:36 +0200 To: "Vishal Moola (Oracle)" Cc: Matthew Wilcox , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Uladzislau Rezki , Andrew Morton Subject: Re: [RFC PATCH] mm/vmalloc: request large order pages from buddy allocator Message-ID: References: <20251014182754.4329-1-vishal.moola@gmail.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: On Wed, Oct 15, 2025 at 02:28:49AM -0700, Vishal Moola (Oracle) wrote: > On Wed, Oct 15, 2025 at 04:56:42AM +0100, Matthew Wilcox wrote: > > On Tue, Oct 14, 2025 at 11:27:54AM -0700, Vishal Moola (Oracle) wrote: > > > Running 1000 iterations of allocations on a small 4GB system finds: > > > > > > 1000 2mb allocations: > > > [Baseline] [This patch] > > > real 46.310s real 34.380s > > > user 0.001s user 0.008s > > > sys 46.058s sys 34.152s > > > > > > 10000 200kb allocations: > > > [Baseline] [This patch] > > > real 56.104s real 43.946s > > > user 0.001s user 0.003s > > > sys 55.375s sys 43.259s > > > > > > 10000 20kb allocations: > > > [Baseline] [This patch] > > > real 0m8.438s real 0m9.160s > > > user 0m0.001s user 0m0.002s > > > sys 0m7.936s sys 0m8.671s > > > > I'd be more confident in the 20kB numbers if you'd done 10x more > > iterations. > > I actually ran my a number of times to mitigate the effects of possibly > too small sample sizes, so I do have that number for you too: > > [Baseline] [This patch] > real 1m28.119s real 1m32.630s > user 0m0.012s user 0m0.011s > sys 1m23.270s sys 1m28.529s > I have just had a look at performance figures of this patch. The test case is 16K allocation by one single thread, 1 000 000 loops, 10 run: sudo ./test_vmalloc.sh run_test_mask=1 nr_threads=1 nr_pages=4 BOX: AMD Milan, 256 CPUs, 512GB of memory # default 16K alloc [ 15.823704] Summary: fix_size_alloc_test passed: 1 failed: 0 xfailed: 0 repeat: 1 loops: 1000000 avg: 955334 usec [ 17.751685] Summary: fix_size_alloc_test passed: 1 failed: 0 xfailed: 0 repeat: 1 loops: 1000000 avg: 1158739 usec [ 19.443759] Summary: fix_size_alloc_test passed: 1 failed: 0 xfailed: 0 repeat: 1 loops: 1000000 avg: 1016522 usec [ 21.035701] Summary: fix_size_alloc_test passed: 1 failed: 0 xfailed: 0 repeat: 1 loops: 1000000 avg: 911381 usec [ 22.727688] Summary: fix_size_alloc_test passed: 1 failed: 0 xfailed: 0 repeat: 1 loops: 1000000 avg: 987286 usec [ 24.199694] Summary: fix_size_alloc_test passed: 1 failed: 0 xfailed: 0 repeat: 1 loops: 1000000 avg: 955112 usec [ 25.755675] Summary: fix_size_alloc_test passed: 1 failed: 0 xfailed: 0 repeat: 1 loops: 1000000 avg: 926393 usec [ 27.355670] Summary: fix_size_alloc_test passed: 1 failed: 0 xfailed: 0 repeat: 1 loops: 1000000 avg: 937875 usec [ 28.979671] Summary: fix_size_alloc_test passed: 1 failed: 0 xfailed: 0 repeat: 1 loops: 1000000 avg: 1006985 usec [ 30.531674] Summary: fix_size_alloc_test passed: 1 failed: 0 xfailed: 0 repeat: 1 loops: 1000000 avg: 941088 usec # the patch 16K alloc [ 44.343380] Summary: fix_size_alloc_test passed: 1 failed: 0 xfailed: 0 repeat: 1 loops: 1000000 avg: 2296849 usec [ 47.171290] Summary: fix_size_alloc_test passed: 1 failed: 0 xfailed: 0 repeat: 1 loops: 1000000 avg: 2014678 usec [ 50.007258] Summary: fix_size_alloc_test passed: 1 failed: 0 xfailed: 0 repeat: 1 loops: 1000000 avg: 2094184 usec [ 52.651141] Summary: fix_size_alloc_test passed: 1 failed: 0 xfailed: 0 repeat: 1 loops: 1000000 avg: 1953046 usec [ 55.455089] Summary: fix_size_alloc_test passed: 1 failed: 0 xfailed: 0 repeat: 1 loops: 1000000 avg: 2209423 usec [ 57.943153] Summary: fix_size_alloc_test passed: 1 failed: 0 xfailed: 0 repeat: 1 loops: 1000000 avg: 1941747 usec [ 60.799043] Summary: fix_size_alloc_test passed: 1 failed: 0 xfailed: 0 repeat: 1 loops: 1000000 avg: 2038504 usec [ 63.299007] Summary: fix_size_alloc_test passed: 1 failed: 0 xfailed: 0 repeat: 1 loops: 1000000 avg: 1788588 usec [ 65.843011] Summary: fix_size_alloc_test passed: 1 failed: 0 xfailed: 0 repeat: 1 loops: 1000000 avg: 2137055 usec [ 68.647031] Summary: fix_size_alloc_test passed: 1 failed: 0 xfailed: 0 repeat: 1 loops: 1000000 avg: 2193022 usec 2X slower. perf-cycles, same test but on 64 CPUs: + 97.02% 0.13% [test_vmalloc] [k] fix_size_alloc_test - 82.11% 82.10% [kernel] [k] native_queued_spin_lock_slowpath 26.19% ret_from_fork_asm ret_from_fork - kthread - 25.96% test_func - fix_size_alloc_test - 23.49% __vmalloc_node_noprof - __vmalloc_node_range_noprof - 54.70% alloc_pages_noprof alloc_pages_mpol __alloc_frozen_pages_noprof get_page_from_freelist __rmqueue_pcplist - 5.58% __get_vm_area_node alloc_vmap_area - 20.54% vfree.part.0 - 20.43% __free_frozen_pages free_frozen_page_commit free_pcppages_bulk _raw_spin_lock_irqsave native_queued_spin_lock_slowpath - 0.77% worker_thread - process_one_work - 0.76% vmstat_update refresh_cpu_vm_stats decay_pcp_high free_pcppages_bulk _raw_spin_lock_irqsave native_queued_spin_lock_slowpath + 76.57% 0.16% [kernel] [k] _raw_spin_lock_irqsave + 71.62% 0.00% [kernel] [k] __vmalloc_node_noprof + 71.61% 0.58% [kernel] [k] __vmalloc_node_range_noprof + 62.35% 0.06% [kernel] [k] alloc_pages_mpol + 62.27% 0.17% [kernel] [k] __alloc_frozen_pages_noprof + 62.20% 0.02% [kernel] [k] alloc_pages_noprof + 62.10% 0.05% [kernel] [k] get_page_from_freelist + 55.63% 0.19% [kernel] [k] __rmqueue_pcplist + 32.11% 0.00% [kernel] [k] ret_from_fork_asm + 32.11% 0.00% [kernel] [k] ret_from_fork + 32.11% 0.00% [kernel] [k] kthread I would say the bottle-neck is a page-allocator. It seems high-order allocations are not good for it. -- Uladzislau Rezki