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Wed, 25 Mar 2026 01:56:03 -0700 (PDT) Received: from milan ([2001:9b1:d5a0:a500::24b]) by smtp.gmail.com with ESMTPSA id 2adb3069b0e04-5a285192b44sm3673978e87.5.2026.03.25.01.56.03 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 25 Mar 2026 01:56:03 -0700 (PDT) From: Uladzislau Rezki X-Google-Original-From: Uladzislau Rezki Date: Wed, 25 Mar 2026 09:56:01 +0100 To: Zi Yan Cc: Muhammad Usama Anjum , Andrew Morton , David Hildenbrand , Lorenzo Stoakes , "Liam R . Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Brendan Jackman , Johannes Weiner , 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 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1D88CFF0-8A74-413F-9A6A-39E27B760AE1@nvidia.com> X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 3950110000C X-Stat-Signature: rjingkkdyjdd4kcmk9jhzhhf77o4b6uh X-Rspam-User: X-HE-Tag: 1774428965-779507 X-HE-Meta: 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 NN52r1lB 5/qCwNAAShTyV1tkFzLHeSu8rTo9mWRbElNso5NxUnJCvsg8QuUnDlPYXe1Xqwa+M7KFTHB1aCfATzy982Z0PBe07Hg== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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. -- Uladzislau Rezki