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Message-ID: <aPEubI4kWvzSC5RN@fedora> Date: Thu, 16 Oct 2025 10:42:04 -0700 From: "Vishal Moola (Oracle)" <vishal.moola@...il.com> To: Uladzislau Rezki <urezki@...il.com> Cc: Matthew Wilcox <willy@...radead.org>, linux-mm@...ck.org, linux-kernel@...r.kernel.org, Andrew Morton <akpm@...ux-foundation.org> Subject: Re: [RFC PATCH] mm/vmalloc: request large order pages from buddy allocator On Thu, Oct 16, 2025 at 06:12:36PM +0200, Uladzislau Rezki wrote: > 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 The reason I didn't use this test module is the same concern Matthew brought up earlier about testing the PCP list rather than buddy allocator. The test module allocates, then frees over and over again, making it incredibly prone to reuse the pages over and over again. > 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
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