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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, david.hildenbrand@arm.com Cc: Ryan Roberts , usama.anjum@arm.com Subject: [PATCH v4 2/3] vmalloc: Optimize vfree Date: Fri, 27 Mar 2026 12:57:14 +0000 Message-ID: <20260327125720.2270651-3-usama.anjum@arm.com> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260327125720.2270651-1-usama.anjum@arm.com> References: <20260327125720.2270651-1-usama.anjum@arm.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Stat-Signature: jft1kh3ib6m3x31p4iebtfczd3wgo1m6 X-Rspamd-Queue-Id: 97E84140003 X-Rspam-User: X-Rspamd-Server: rspam03 X-HE-Tag: 1774616262-115910 X-HE-Meta: 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 DxzpFIti 3km2JGarVzmaj7bsxCOdcCQMQJFbmSlSZj1AXXrLJoIDlrrK1b6E6VeHmnNGbMYhDxyEY2aHWbfoI6XUtExzJqgzX7PVYyl5tutspiDTXuHYv8oa1fJr1Zr4lcvzNZDytSZGdjHdtTtROyAM/NWXHHQ1AjgqECEwXOOb9nEYiIvlB8beA5AukeQ0/08QUCRQXS97hSw8ygDi2975Xmk3mm3YIEy4gQSY2FMiOID8bH03pKZojWBkD3j0aunMYvrGemjtGbjc36SlTCX0E83ZvaxVobm/xmANXPW+tv2XOxW0agmqjRYMGXkX1O5fUhxjNMEEZ Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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++; + } + } + if (nr_contig) + __free_contig_range(start_pfn, nr_contig); +} + /* * This is the 'heart' of the zoned buddy allocator. */ diff --git a/mm/vmalloc.c b/mm/vmalloc.c index c607307c657a6..e9b3d6451e48b 100644 --- a/mm/vmalloc.c +++ b/mm/vmalloc.c @@ -3459,19 +3459,13 @@ void vfree(const void *addr) if (unlikely(vm->flags & VM_FLUSH_RESET_PERMS)) vm_reset_perms(vm); - for (i = 0; i < vm->nr_pages; i++) { - struct page *page = vm->pages[i]; - BUG_ON(!page); - /* - * High-order allocs for huge vmallocs are split, so - * can be freed as an array of order-0 allocations - */ - if (!(vm->flags & VM_MAP_PUT_PAGES)) - mod_lruvec_page_state(page, NR_VMALLOC, -1); - __free_page(page); - cond_resched(); + if (!(vm->flags & VM_MAP_PUT_PAGES)) { + for (i = 0; i < vm->nr_pages; i++) + mod_lruvec_page_state(vm->pages[i], NR_VMALLOC, -1); } + free_pages_bulk(vm->pages, vm->nr_pages); + kvfree(vm->pages); kfree(vm); } -- 2.47.3