From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 8CDA73A6EE7; Tue, 31 Mar 2026 10:08:33 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774951713; cv=none; b=luIu87n9mP6wiCfKuQ2dOUFAQlLnn7Ru0yPp0Ic0qrPJX3G0w34XiPblxw9JJhJca2JiLeUEvDAf9KvN+QAsxlKNk2MlvnTrx36/+5kZhBOfVJOqyXYPT4qJecJtE9tpuHVHhgVlXkeWp1EXe09dQTNPt3ZQITkE63uVjDTPWKA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774951713; c=relaxed/simple; bh=KeW6+KSmsFuP31VKS323ds73C2gVkWBlh6+eIeZz1zU=; h=Message-ID:Date:MIME-Version:Subject:To:References:From: In-Reply-To:Content-Type; b=B7iXSYg7xg8jnhLnDX50+l2udWYa/HevEJtN/zteIQBp9O2xhMY9eAj2+iZ+QWjO0ohTcVRUlaWsyP1AunsqgRYkk1iJ8RRamJDu12Xa7Tmlftdp4EpYvqc7y6cPrfjtq+28X5NLPDASnnuNWakcNSQukMfCPiR97RE14ovtbuM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=A0bVWovP; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="A0bVWovP" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 17D1FC2BCB0; Tue, 31 Mar 2026 10:08:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1774951713; bh=KeW6+KSmsFuP31VKS323ds73C2gVkWBlh6+eIeZz1zU=; h=Date:Subject:To:References:From:In-Reply-To:From; b=A0bVWovPflIepW+0gqqv+pevlEcjTX8exWUX7OJtpeXYN7hKcnTOsturfBwnG4Shu 4Mo0kgre4iAH5f+RiSzNG4VJEz4zwhwtHq1HrbiY3yqjmptDmOvzxAi7IUWaAOzeHe Qqc093uFr4IySwX2AqS2L5pulK3rwgdCdVjGFmYvj7EmWQaWOuIJAnzPnQz4WK4dhQ 39ALj0ACw0v3mv63+3mxf9DhaZ2AFWoTmXiCy+Qcrnk2sfrp57op5guSbjrSKHWqBp 9koxfcTi2G1VrrLL1Nxp0OySOl4MyI76HACT9moLK+65VeenrX7/etdpMbKrK67MWk vu4QcRTxwYX2A== Message-ID: Date: Tue, 31 Mar 2026 12:08:26 +0200 Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 2/3] vmalloc: Optimize vfree To: Muhammad Usama Anjum , "David Hildenbrand (Arm)" , Andrew Morton , Lorenzo Stoakes , "Liam R . Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Brendan Jackman , Johannes Weiner , Zi Yan , Uladzislau Rezki , Nick Terrell , David Sterba , Vishal Moola , linux-mm@kvack.org, linux-kernel@vger.kernel.org, bpf@vger.kernel.org, Ryan.Roberts@arm.com References: <20260327125720.2270651-1-usama.anjum@arm.com> <20260327125720.2270651-3-usama.anjum@arm.com> <82e4055c-2343-49ee-b772-d3f4d134f8d0@kernel.org> <7eb26b81-ec64-470c-9fd2-52f9b9692b48@arm.com> From: David Hildenbrand Content-Language: en-US In-Reply-To: <7eb26b81-ec64-470c-9fd2-52f9b9692b48@arm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 3/30/26 18:15, Muhammad Usama Anjum wrote: > On 30/03/2026 3:38 pm, David Hildenbrand (Arm) wrote: >> On 3/27/26 13:57, Muhammad Usama Anjum wrote: >>> From: Ryan Roberts >>> >>> Whenever vmalloc allocates high order pages (e.g. for a huge mapping) it >>> must immediately split_page() to order-0 so that it remains compatible >>> with users that want to access the underlying struct page. >>> Commit a06157804399 ("mm/vmalloc: request large order pages from buddy >>> allocator") recently made it much more likely for vmalloc to allocate >>> high order pages which are subsequently split to order-0. >>> >>> Unfortunately this had the side effect of causing performance >>> regressions for tight vmalloc/vfree loops (e.g. test_vmalloc.ko >>> benchmarks). See Closes: tag. This happens because the high order pages >>> must be gotten from the buddy but then because they are split to >>> order-0, when they are freed they are freed to the order-0 pcp. >>> Previously allocation was for order-0 pages so they were recycled from >>> the pcp. >>> >>> It would be preferable if when vmalloc allocates an (e.g.) order-3 page >>> that it also frees that order-3 page to the order-3 pcp, then the >>> regression could be removed. >>> >>> So let's do exactly that; update stats separately first as coalescing is >>> hard to do correctly without complexity. Use free_pages_bulk() which uses >>> the new __free_contig_range() API to batch-free contiguous ranges of pfns. >>> This not only removes the regression, but significantly improves >>> performance of vfree beyond the baseline. >>> >>> A selection of test_vmalloc benchmarks running on arm64 server class >>> system. mm-new is the baseline. Commit a06157804399 ("mm/vmalloc: request >>> large order pages from buddy allocator") was added in v6.19-rc1 where we >>> see regressions. Then with this change performance is much better. (>0 >>> is faster, <0 is slower, (R)/(I) = statistically significant >>> Regression/Improvement): >>> >>> +-----------------+----------------------------------------------------------+-------------------+--------------------+ >>> | Benchmark | Result Class | mm-new | this series | >>> +=================+==========================================================+===================+====================+ >>> | micromm/vmalloc | fix_align_alloc_test: p:1, h:0, l:500000 (usec) | 1331843.33 | (I) 67.17% | >>> | | fix_size_alloc_test: p:1, h:0, l:500000 (usec) | 415907.33 | -5.14% | >>> | | fix_size_alloc_test: p:4, h:0, l:500000 (usec) | 755448.00 | (I) 53.55% | >>> | | fix_size_alloc_test: p:16, h:0, l:500000 (usec) | 1591331.33 | (I) 57.26% | >>> | | fix_size_alloc_test: p:16, h:1, l:500000 (usec) | 1594345.67 | (I) 68.46% | >>> | | fix_size_alloc_test: p:64, h:0, l:100000 (usec) | 1071826.00 | (I) 79.27% | >>> | | fix_size_alloc_test: p:64, h:1, l:100000 (usec) | 1018385.00 | (I) 84.17% | >>> | | fix_size_alloc_test: p:256, h:0, l:100000 (usec) | 3970899.67 | (I) 77.01% | >>> | | fix_size_alloc_test: p:256, h:1, l:100000 (usec) | 3821788.67 | (I) 89.44% | >>> | | fix_size_alloc_test: p:512, h:0, l:100000 (usec) | 7795968.00 | (I) 82.67% | >>> | | fix_size_alloc_test: p:512, h:1, l:100000 (usec) | 6530169.67 | (I) 118.09% | >>> | | full_fit_alloc_test: p:1, h:0, l:500000 (usec) | 626808.33 | -0.98% | >>> | | kvfree_rcu_1_arg_vmalloc_test: p:1, h:0, l:500000 (usec) | 532145.67 | -1.68% | >>> | | kvfree_rcu_2_arg_vmalloc_test: p:1, h:0, l:500000 (usec) | 537032.67 | -0.96% | >>> | | long_busy_list_alloc_test: p:1, h:0, l:500000 (usec) | 8805069.00 | (I) 74.58% | >>> | | pcpu_alloc_test: p:1, h:0, l:500000 (usec) | 500824.67 | 4.35% | >>> | | random_size_align_alloc_test: p:1, h:0, l:500000 (usec) | 1637554.67 | (I) 76.99% | >>> | | random_size_alloc_test: p:1, h:0, l:500000 (usec) | 4556288.67 | (I) 72.23% | >>> | | vm_map_ram_test: p:1, h:0, l:500000 (usec) | 107371.00 | -0.70% | >>> +-----------------+----------------------------------------------------------+-------------------+--------------------+ >>> >>> Fixes: a06157804399 ("mm/vmalloc: request large order pages from buddy allocator") >>> Closes: https://lore.kernel.org/all/66919a28-bc81-49c9-b68f-dd7c73395a0d@arm.com/ >>> Acked-by: Zi Yan >>> Signed-off-by: Ryan Roberts >>> Co-developed-by: Muhammad Usama Anjum >>> Signed-off-by: Muhammad Usama Anjum >>> --- >>> Changes since v3: >>> - Add kerneldoc comment and update description >>> - Add tag >>> >>> Changes since v2: >>> - Remove BUG_ON in favour of simple implementation as this has never >>> been seen to output any bug in the past as well >>> - Move the free loop to separate function, free_pages_bulk() >>> - Update stats, lruvec_stat in separate loop >>> >>> Changes since v1: >>> - Rebase on mm-new >>> - Rerun benchmarks >>> --- >>> include/linux/gfp.h | 2 ++ >>> mm/page_alloc.c | 38 ++++++++++++++++++++++++++++++++++++++ >>> mm/vmalloc.c | 16 +++++----------- >>> 3 files changed, 45 insertions(+), 11 deletions(-) >>> >>> diff --git a/include/linux/gfp.h b/include/linux/gfp.h >>> index 7c1f9da7c8e56..71f9097ab99a0 100644 >>> --- a/include/linux/gfp.h >>> +++ b/include/linux/gfp.h >>> @@ -239,6 +239,8 @@ unsigned long alloc_pages_bulk_noprof(gfp_t gfp, int preferred_nid, >>> struct page **page_array); >>> #define __alloc_pages_bulk(...) alloc_hooks(alloc_pages_bulk_noprof(__VA_ARGS__)) >>> >>> +void free_pages_bulk(struct page **page_array, unsigned long nr_pages); >>> + >>> unsigned long alloc_pages_bulk_mempolicy_noprof(gfp_t gfp, >>> unsigned long nr_pages, >>> struct page **page_array); >>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c >>> index 18a96b51aa0be..64be8a9019dca 100644 >>> --- a/mm/page_alloc.c >>> +++ b/mm/page_alloc.c >>> @@ -5175,6 +5175,44 @@ unsigned long alloc_pages_bulk_noprof(gfp_t gfp, int preferred_nid, >>> } >>> EXPORT_SYMBOL_GPL(alloc_pages_bulk_noprof); >>> >>> +/* >>> + * free_pages_bulk - Free an array of order-0 pages >>> + * @page_array: Array of pages to free >>> + * @nr_pages: The number of pages in the array >>> + * >>> + * Free the order-0 pages. Adjacent entries whose PFNs form a contiguous >>> + * run are released with a single __free_contig_range() call. >>> + * >>> + * This assumes page_array is sorted in ascending PFN order. Without that, >>> + * the function still frees all pages, but contiguous runs may not be >>> + * detected and the freeing pattern can degrade to freeing one page at a >>> + * time. >>> + * >>> + * Context: Sleepable process context only; calls cond_resched() >>> + */ >>> +void free_pages_bulk(struct page **page_array, unsigned long nr_pages) >>> +{ >>> + unsigned long start_pfn = 0, pfn; >>> + unsigned long i, nr_contig = 0; >>> + >>> + for (i = 0; i < nr_pages; i++) { >>> + pfn = page_to_pfn(page_array[i]); >>> + if (!nr_contig) { >>> + start_pfn = pfn; >>> + nr_contig = 1; >>> + } else if (start_pfn + nr_contig != pfn) { >>> + __free_contig_range(start_pfn, nr_contig); >>> + start_pfn = pfn; >>> + nr_contig = 1; >>> + cond_resched(); >>> + } else { >>> + nr_contig++; >>> + } >>> + } >> >> What happened to the idea of using num_pages_contiguous()? I think that >> should generate more efficient code (all we're doing is comparing >> pointers really on SPARSEMEM_VMEMMAP) and the end result looks more >> readable? > Sorry, I misunderstood you in the light of duplicate usage of > num_pages_contiguous(). I'll update the implementation. A note that it should even speedup SPARSEMEM && !SPARSEMEM_VMEMMAP, where a page_to_pfn() is expensive and best minimized/avoided :) -- Cheers, David