From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 2E29031283A for ; Thu, 18 Dec 2025 11:12:18 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1766056341; cv=none; b=ZZsWepb54LWNx2QvzTLsDKL9Mes0fjI66CpL8wyp/BcwGvje6hSTTrNjD26WX97kRjdv74GA+qASw2K3+vbD3GjhFTDZGG25Ts1fWX4aUQLoLfe7NHvBMzalxkmM1GlrMaIX4GGvwsb6PLkGPfMgI2nU4IKMggDhckhKfWFlxAw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1766056341; c=relaxed/simple; bh=W53EjW/3n8Dir1jvngbbtLA5OpIbripfUJKUkXPtHg0=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=Mgp6E7FOfRCaBGGO92A3OixHU1qHSSZ9TB9MPjd0fx632O4V7MD2htqjNkxRaTRG7yQeZCSg8Fzuh/5vw5EB0Cehk2ZCRFMdvBzw6mD8EHsctBggksw+RRt7drnkuG0dg9AMlwX0jtguP2Ix38VV29OGdFrMZWoDNte+Qzk0nOE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 0C158FEC; Thu, 18 Dec 2025 03:12:11 -0800 (PST) Received: from [10.1.39.180] (unknown [10.1.39.180]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 2A64A3F73F; Thu, 18 Dec 2025 03:12:17 -0800 (PST) Message-ID: <37efa0a9-99bc-4099-ba64-2474f3f09aa2@arm.com> Date: Thu, 18 Dec 2025 11:12:15 +0000 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 2/2] mm/vmalloc: Add attempt_larger_order_alloc parameter Content-Language: en-GB To: Uladzislau Rezki Cc: linux-mm@kvack.org, Andrew Morton , Vishal Moola , Dev Jain , Baoquan He , LKML References: <20251216211921.1401147-1-urezki@gmail.com> <20251216211921.1401147-2-urezki@gmail.com> <6ca6e796-cded-4221-b1f8-92176a80513e@arm.com> <0f69442d-b44e-4b30-b11e-793511db9f1e@arm.com> <4a66f13d-318b-4cdb-b168-0c993ff8a309@arm.com> From: Ryan Roberts In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 17/12/2025 19:22, Uladzislau Rezki wrote: > On Wed, Dec 17, 2025 at 05:01:19PM +0000, Ryan Roberts wrote: >> On 17/12/2025 15:20, Ryan Roberts wrote: >>> On 17/12/2025 12:02, Uladzislau Rezki wrote: >>>>> On 16/12/2025 21:19, Uladzislau Rezki (Sony) wrote: >>>>>> Introduce a module parameter to enable or disable the large-order >>>>>> allocation path in vmalloc. High-order allocations are disabled by >>>>>> default so far, but users may explicitly enable them at runtime if >>>>>> desired. >>>>>> >>>>>> High-order pages allocated for vmalloc are immediately split into >>>>>> order-0 pages and later freed as order-0, which means they do not >>>>>> feed the per-CPU page caches. As a result, high-order attempts tend >>>>>> to bypass the PCP fastpath and fall back to the buddy allocator that >>>>>> can affect performance. >>>>>> >>>>>> However, when the PCP caches are empty, high-order allocations may >>>>>> show better performance characteristics especially for larger >>>>>> allocation requests. >>>>> >>>>> I wonder if a better solution would be "allocate order-0 if available in pcp, >>>>> else try large order, else fallback to order-0" Could that provide the best of >>>>> all worlds without needing a configuration knob? >>>>> >>>> I am not sure, to me it looks like a bit odd. >>> >>> Perhaps it would feel better if it was generalized to "first try allocation from >>> PCP list, highest to lowest order, then try allocation from the buddy, highest >>> to lowest order"? >>> >>>> Ideally it would be >>>> good just free it as high-order page and not order-0 peaces. >>> >>> Yeah perhaps that's better. How about something like this (very lightly tested >>> and no performance results yet): >>> >>> (And I should admit I'm not 100% sure it is safe to call free_frozen_pages() >>> with a contiguous run of order-0 pages, but I'm not seeing any warnings or >>> memory leaks when running mm selftests...) >>> >>> ---8<--- >>> commit caa3e5eb5bfade81a32fa62d1a8924df1eb0f619 >>> Author: Ryan Roberts >>> Date: Wed Dec 17 15:11:08 2025 +0000 >>> >>> WIP >>> >>> Signed-off-by: Ryan Roberts >>> >>> diff --git a/include/linux/gfp.h b/include/linux/gfp.h >>> index b155929af5b1..d25f5b867e6b 100644 >>> --- a/include/linux/gfp.h >>> +++ b/include/linux/gfp.h >>> @@ -383,6 +383,8 @@ extern void __free_pages(struct page *page, unsigned int order); >>> extern void free_pages_nolock(struct page *page, unsigned int order); >>> extern void free_pages(unsigned long addr, unsigned int order); >>> >>> +void free_pages_bulk(struct page *page, int nr_pages); >>> + >>> #define __free_page(page) __free_pages((page), 0) >>> #define free_page(addr) free_pages((addr), 0) >>> >>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c >>> index 822e05f1a964..5f11224cf353 100644 >>> --- a/mm/page_alloc.c >>> +++ b/mm/page_alloc.c >>> @@ -5304,6 +5304,48 @@ static void ___free_pages(struct page *page, unsigned int >>> order, >>> } >>> } >>> >>> +static void free_frozen_pages_bulk(struct page *page, int nr_pages) >>> +{ >>> + while (nr_pages) { >>> + unsigned int fit_order, align_order, order; >>> + unsigned long pfn; >>> + >>> + pfn = page_to_pfn(page); >>> + fit_order = ilog2(nr_pages); >>> + align_order = pfn ? __ffs(pfn) : fit_order; >>> + order = min3(fit_order, align_order, MAX_PAGE_ORDER); >>> + >>> + free_frozen_pages(page, order); >>> + >>> + page += 1U << order; >>> + nr_pages -= 1U << order; >>> + } >>> +} >>> + >>> +void free_pages_bulk(struct page *page, int nr_pages) >>> +{ >>> + struct page *start = NULL; >>> + bool can_free; >>> + int i; >>> + >>> + for (i = 0; i < nr_pages; i++, page++) { >>> + VM_BUG_ON_PAGE(PageHead(page), page); >>> + VM_BUG_ON_PAGE(PageTail(page), page); >>> + >>> + can_free = put_page_testzero(page); >>> + >>> + if (!can_free && start) { >>> + free_frozen_pages_bulk(start, page - start); >>> + start = NULL; >>> + } else if (can_free && !start) { >>> + start = page; >>> + } >>> + } >>> + >>> + if (start) >>> + free_frozen_pages_bulk(start, page - start); >>> +} >>> + >>> /** >>> * __free_pages - Free pages allocated with alloc_pages(). >>> * @page: The page pointer returned from alloc_pages(). >>> diff --git a/mm/vmalloc.c b/mm/vmalloc.c >>> index ecbac900c35f..8f782bac1ece 100644 >>> --- a/mm/vmalloc.c >>> +++ b/mm/vmalloc.c >>> @@ -3429,7 +3429,8 @@ void vfree_atomic(const void *addr) >>> void vfree(const void *addr) >>> { >>> struct vm_struct *vm; >>> - int i; >>> + struct page *start; >>> + int i, nr; >>> >>> if (unlikely(in_interrupt())) { >>> vfree_atomic(addr); >>> @@ -3455,17 +3456,26 @@ void vfree(const void *addr) >>> /* All pages of vm should be charged to same memcg, so use first one. */ >>> if (vm->nr_pages && !(vm->flags & VM_MAP_PUT_PAGES)) >>> mod_memcg_page_state(vm->pages[0], MEMCG_VMALLOC, -vm->nr_pages); >>> - for (i = 0; i < vm->nr_pages; i++) { >>> + >>> + start = vm->pages[0]; >>> + BUG_ON(!start); >>> + nr = 1; >>> + for (i = 1; 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 >>> - */ >>> - __free_page(page); >>> - cond_resched(); >>> + >>> + if (start + nr != page) { >>> + free_pages_bulk(start, nr); >>> + start = page; >>> + nr = 1; >>> + cond_resched(); >>> + } else { >>> + nr++; >>> + } >>> } >>> + free_pages_bulk(start, nr); >>> + >>> if (!(vm->flags & VM_MAP_PUT_PAGES)) >>> atomic_long_sub(vm->nr_pages, &nr_vmalloc_pages); >>> kvfree(vm->pages); >>> ---8<--- >> >> I tested this on a performance monitoring system and see a huge improvement for >> the test_vmalloc tests. >> >> Both columns are compared to v6.18. 6-19-0-rc1 has Vishal's change to allocate >> large orders, which I previously reported the regressions for. vfree-high-order >> adds the above patch to free contiguous order-0 pages in bulk. >> >> (R)/(I) means statistically significant regression/improvement. Results are >> normalized so that less than zero is regression and greater than zero is >> improvement. >> >> +-----------------+----------------------------------------------------------+--------------+------------------+ >> | Benchmark | Result Class | 6-19-0-rc1 | vfree-high-order | >> +=================+==========================================================+==============+==================+ >> | micromm/vmalloc | fix_align_alloc_test: p:1, h:0, l:500000 (usec) | (R) -40.69% | (I) 3.98% | >> | | fix_size_alloc_test: p:1, h:0, l:500000 (usec) | 0.10% | -1.47% | >> | | fix_size_alloc_test: p:4, h:0, l:500000 (usec) | (R) -22.74% | (I) 11.57% | >> | | fix_size_alloc_test: p:16, h:0, l:500000 (usec) | (R) -23.63% | (I) 47.42% | >> | | fix_size_alloc_test: p:16, h:1, l:500000 (usec) | -1.58% | (I) 106.01% | >> | | fix_size_alloc_test: p:64, h:0, l:100000 (usec) | (R) -24.39% | (I) 99.12% | >> | | fix_size_alloc_test: p:64, h:1, l:100000 (usec) | (I) 2.34% | (I) 196.87% | >> | | fix_size_alloc_test: p:256, h:0, l:100000 (usec) | (R) -23.29% | (I) 125.42% | >> | | fix_size_alloc_test: p:256, h:1, l:100000 (usec) | (I) 3.74% | (I) 238.59% | >> | | fix_size_alloc_test: p:512, h:0, l:100000 (usec) | (R) -23.80% | (I) 132.38% | >> | | fix_size_alloc_test: p:512, h:1, l:100000 (usec) | (R) -2.84% | (I) 514.75% | >> | | full_fit_alloc_test: p:1, h:0, l:500000 (usec) | 2.74% | 0.33% | >> | | kvfree_rcu_1_arg_vmalloc_test: p:1, h:0, l:500000 (usec) | 0.58% | 1.36% | >> | | kvfree_rcu_2_arg_vmalloc_test: p:1, h:0, l:500000 (usec) | -0.66% | 1.48% | >> | | long_busy_list_alloc_test: p:1, h:0, l:500000 (usec) | (R) -25.24% | (I) 77.95% | >> | | pcpu_alloc_test: p:1, h:0, l:500000 (usec) | -0.58% | 0.60% | >> | | random_size_align_alloc_test: p:1, h:0, l:500000 (usec) | (R) -45.75% | (I) 8.51% | >> | | random_size_alloc_test: p:1, h:0, l:500000 (usec) | (R) -28.16% | (I) 65.34% | >> | | vm_map_ram_test: p:1, h:0, l:500000 (usec) | -0.54% | -0.33% | >> +-----------------+----------------------------------------------------------+--------------+------------------+ >> >> What do you think? >> > You were first :) > > Some figures from me: > > # Default(3 pages) What is Default? I'm guessing it's the state prior to Vishal's patch? > fix_size_alloc_test passed: 1 failed: 0 xfailed: 0 repeat: 1 loops: 1000000 avg: 541868 usec > fix_size_alloc_test passed: 1 failed: 0 xfailed: 0 repeat: 1 loops: 1000000 avg: 542515 usec > fix_size_alloc_test passed: 1 failed: 0 xfailed: 0 repeat: 1 loops: 1000000 avg: 541561 usec > fix_size_alloc_test passed: 1 failed: 0 xfailed: 0 repeat: 1 loops: 1000000 avg: 542951 usec > > # Patch(3 pages) What is Patch? I'm guessing state after applying both Vishal's and my patches? > fix_size_alloc_test passed: 1 failed: 0 xfailed: 0 repeat: 1 loops: 1000000 avg: 585266 usec > fix_size_alloc_test passed: 1 failed: 0 xfailed: 0 repeat: 1 loops: 1000000 avg: 594301 usec > fix_size_alloc_test passed: 1 failed: 0 xfailed: 0 repeat: 1 loops: 1000000 avg: 598912 usec > fix_size_alloc_test passed: 1 failed: 0 xfailed: 0 repeat: 1 loops: 1000000 avg: 589345 usec > > Now the perf figures are almost settled and aligned with default! > We do use per-cpu-cache for 3 pages allocations. > > # Default(100 pages) > fix_size_alloc_test passed: 1 failed: 0 xfailed: 0 repeat: 1 loops: 1000000 avg: 5724919 usec > fix_size_alloc_test passed: 1 failed: 0 xfailed: 0 repeat: 1 loops: 1000000 avg: 5721430 usec > fix_size_alloc_test passed: 1 failed: 0 xfailed: 0 repeat: 1 loops: 1000000 avg: 5717224 usec > > # Patch(100 pages) > fix_size_alloc_test passed: 1 failed: 0 xfailed: 0 repeat: 1 loops: 1000000 avg: 2629600 usec > fix_size_alloc_test passed: 1 failed: 0 xfailed: 0 repeat: 1 loops: 1000000 avg: 2622811 usec > fix_size_alloc_test passed: 1 failed: 0 xfailed: 0 repeat: 1 loops: 1000000 avg: 2629324 usec > > ~2x faster! It is because of freeing now occurs much more efficient > so we spent less cycles on free path comparing with default case. > > See below, perf also confirms that vfree() ~2x consumes less cycles: > > # Default > + 96.99% 0.49% [test_vmalloc] [k] fix_size_alloc_test > + 59.64% 2.38% [kernel] [k] vfree.part.0 > + 45.69% 15.80% [kernel] [k] __free_frozen_pages > + 39.83% 0.00% [kernel] [k] ret_from_fork_asm > + 39.83% 0.00% [kernel] [k] ret_from_fork > + 39.83% 0.00% [kernel] [k] kthread > + 38.67% 0.00% [test_vmalloc] [k] test_func > + 36.64% 0.01% [kernel] [k] __vmalloc_node_noprof > + 36.63% 0.20% [kernel] [k] __vmalloc_node_range_noprof > + 17.55% 4.94% [kernel] [k] alloc_pages_bulk_noprof > + 16.46% 12.21% [kernel] [k] free_frozen_page_commit.isra.0 > + 16.06% 8.09% [kernel] [k] vmap_small_pages_range_noflush > + 12.56% 10.82% [kernel] [k] __rmqueue_pcplist > + 9.45% 9.43% [kernel] [k] __get_pfnblock_flags_mask.isra.0 > + 7.95% 7.95% [kernel] [k] pfn_valid > + 5.77% 0.03% [kernel] [k] remove_vm_area > + 5.44% 5.44% [kernel] [k] ___free_pages > + 4.67% 4.59% [kernel] [k] __vunmap_range_noflush > + 4.30% 4.30% [kernel] [k] __list_add_valid_or_report > > # Patch > + 94.28% 1.00% [test_vmalloc] [k] fix_size_alloc_test > + 55.63% 0.03% [kernel] [k] __vmalloc_node_noprof > + 55.60% 3.78% [kernel] [k] __vmalloc_node_range_noprof > + 37.26% 19.29% [kernel] [k] vmap_small_pages_range_noflush > + 37.12% 5.63% [kernel] [k] vfree.part.0 > + 30.59% 0.00% [kernel] [k] ret_from_fork_asm > + 30.59% 0.00% [kernel] [k] ret_from_fork > + 30.59% 0.00% [kernel] [k] kthread > + 28.79% 0.00% [test_vmalloc] [k] test_func > + 17.90% 17.88% [kernel] [k] pfn_valid > + 13.24% 0.02% [kernel] [k] remove_vm_area > + 10.90% 10.68% [kernel] [k] __vunmap_range_noflush > + 10.81% 10.80% [kernel] [k] free_pages_bulk > + 7.09% 0.51% [kernel] [k] alloc_pages_noprof > + 6.58% 0.41% [kernel] [k] alloc_pages_mpol > + 6.50% 0.30% [kernel] [k] free_frozen_pages_bulk > + 5.74% 0.97% [kernel] [k] __alloc_frozen_pages_noprof > + 5.70% 0.00% [kernel] [k] worker_thread > + 5.62% 0.02% [kernel] [k] process_one_work > + 5.57% 0.01% [kernel] [k] __purge_vmap_area_lazy > + 4.76% 2.55% [kernel] [k] get_page_from_freelist > > So it is nice :) > > -- > Uladzislau Rezki