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Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Brendan Jackman , Johannes Weiner , 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 Subject: Re: [PATCH v3 2/3] vmalloc: Optimize vfree Message-ID: References: <20260324133538.497616-1-usama.anjum@arm.com> <20260324133538.497616-3-usama.anjum@arm.com> <1D88CFF0-8A74-413F-9A6A-39E27B760AE1@nvidia.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, Mar 25, 2026 at 03:02:14PM +0000, Muhammad Usama Anjum wrote: > On 25/03/2026 8:56 am, Uladzislau Rezki wrote: > > On Tue, Mar 24, 2026 at 10:55:55AM -0400, Zi Yan wrote: > >> On 24 Mar 2026, at 9:35, 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; use 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/ > >>> Signed-off-by: Ryan Roberts > >>> Co-developed-by: Muhammad Usama Anjum > >>> Signed-off-by: Muhammad Usama Anjum > >>> --- > >>> 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 > >>> > >>> Made-with: Cursor > >>> --- > >>> include/linux/gfp.h | 2 ++ > >>> mm/page_alloc.c | 23 +++++++++++++++++++++++ > >>> mm/vmalloc.c | 16 +++++----------- > >>> 3 files changed, 30 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 eedce9a30eb7e..250cc07e547b8 100644 > >>> --- a/mm/page_alloc.c > >>> +++ b/mm/page_alloc.c > >>> @@ -5175,6 +5175,29 @@ unsigned long alloc_pages_bulk_noprof(gfp_t gfp, int preferred_nid, > >>> } > >>> EXPORT_SYMBOL_GPL(alloc_pages_bulk_noprof); > >>> > >>> +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(); > >> > > It will cause schedule while atomic. Have you checked that > > __free_contig_range() also can sleep? Of so then we are aligned, if not > > probably we should remove it. > Sorry, I didn't get it. How does having cond_resched() in this function > affects __free_contig_range()? > It is not. What i am asking is about: spin_lock(); free_pages_bulk() ... so this is not allowed because there is cond_resched() call. We can remove it and make it possible to invoke free_pages_bulk() under spin-lock, __but__ only if for example other calls do not sleep: __free_contig_range() memdesc_section() free_prepared_contig_range() ... > > The current user of this function is only vfree() which is sleepable. > I know. But this function can be used by others soon or later. Another option is add a comment, saying that it is only for sleepable contexts. -- Uladzislau Rezki