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Wed, 01 Apr 2026 08:13:16 -0700 (PDT) Received: from milan ([2001:9b1:d5a0:a500::24b]) by smtp.gmail.com with ESMTPSA id 2adb3069b0e04-5a2c6cc5f90sm4157e87.49.2026.04.01.08.13.09 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 01 Apr 2026 08:13:10 -0700 (PDT) From: Uladzislau Rezki X-Google-Original-From: Uladzislau Rezki Date: Wed, 1 Apr 2026 17:13:07 +0200 To: Muhammad Usama Anjum Cc: Andrew Morton , David Hildenbrand , 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, david.hildenbrand@arm.com Subject: Re: [PATCH v6 2/3] vmalloc: Optimize vfree with free_pages_bulk() Message-ID: References: <20260401101634.2868165-1-usama.anjum@arm.com> <20260401101634.2868165-3-usama.anjum@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260401101634.2868165-3-usama.anjum@arm.com> X-Rspam-User: X-Rspamd-Queue-Id: E0CBC4000B X-Stat-Signature: ipexe19wya15o5wydni3664qdoa5ria1 X-Rspamd-Server: rspam06 X-HE-Tag: 1775056398-262663 X-HE-Meta: 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 MZ7QBGHj 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Apr 01, 2026 at 11:16:20AM +0100, 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: Vlastimil Babka (SUSE) > Acked-by: Zi Yan > Signed-off-by: Ryan Roberts > Co-developed-by: Muhammad Usama Anjum > Signed-off-by: Muhammad Usama Anjum > --- > Changes since v5: > - Change subject > > Changes since v4: > - Use num_pages_contiguous() instead of raw loop > > 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 | 28 ++++++++++++++++++++++++++++ > mm/vmalloc.c | 16 +++++----------- > 3 files changed, 35 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 fb4522ba51faf..6568af69b5cdb 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -5175,6 +5175,34 @@ 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) > +{ > + while (nr_pages) { > + unsigned long nr_contig = num_pages_contiguous(page_array, nr_pages); > + > + __free_contig_range(page_to_pfn(*page_array), nr_contig); > + > + nr_pages -= nr_contig; > + page_array += nr_contig; > + cond_resched(); > + } > +} > + > /* > * 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 > LGTM: At least vmalloc change I do not see any concern(mentioned by AI) if mod_lruvec_page_state(); is invoked in loop without cond_resched(). The operation is light and nr_pages can not be millions of pages. Reviewed-by: Uladzislau Rezki (Sony) -- Uladzislau Rezki