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Message-ID: <aPFBY_OtG0YTAaHv@fedora> Date: Thu, 16 Oct 2025 12:02:59 -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 10:42:04AM -0700, Vishal Moola (Oracle) wrote: > 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. Ah also just took a closer look at this. I realize that you also did 16k allocations (which is at most order-2), so it may not be a good representation of high-order allocations either. Plus that falls into the regression range I found that I detailed in response to Matthew elsewhere (I've copy pasted it here for reference) I ended up finding that allocating sizes <=20k had noticeable regressions, while [20k, 90k] was approximately the same, and >= 90k had improvements (getting more and more noticeable as size grows in magnitude). > > -- > > Uladzislau Rezki
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