From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 2471A36897B for ; Fri, 20 Mar 2026 10:08:55 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774001336; cv=none; b=GEZO4v6n90OT74X9At4oGX9PqE242wIwfwk6gvDRuLJNOzSUmtdQP3TzBVATf3OkjrqU6Y4s753eZIskDviXqaGl6dTq9pzWystboWvPzKZxV1DmU5PwjF5YCDSpTeBqq0aEgl6cUzFXm3Ucv4EBlscwXXYmBFuX35gc2efFGOU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774001336; c=relaxed/simple; bh=GHXK4cL8G6huHh3bZExopaK3L+IrDeQMp6F3V1JuQjM=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=RgxgQZStzGgZIFlebMQ7ewUhHXBKRxK6DFQp0gnFFYqLMBj/xA/eUg55z3OdNkxU4BfkaeZgWz1PUMi1ck/QhUiHVxPiiU3u8echkKj3ydugwct42Iwy7rK0wXeWSZdsZFy94api4/qz55B29DzAMWxuoNXfEwjt/K66I8tE63M= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=IJQM5ROq; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="IJQM5ROq" Received: by smtp.kernel.org (Postfix) with ESMTPSA id DA8D3C4CEF7; Fri, 20 Mar 2026 10:08:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1774001335; bh=GHXK4cL8G6huHh3bZExopaK3L+IrDeQMp6F3V1JuQjM=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=IJQM5ROqb8W0WDCmr+pHfaRt3XF4XzdYnjPbAW9hrFllS1RIF7cFUmKGPmZygwxjv RCD2I1evj3o3aclTr3lKV+KSzSCmIQPUiKTa+Z5gBQ61tNj5MzuBfg+K2SPmiizG5B i3QTrSxa51XEFQ0uMyaiyyvCdeF7ImNQPBF07lWU5MyE2A8cfxjpSDw1HNr3K+/2ve ZUg981zwnNv9OpNnO2r4kGFiVSazeXPTjTieyZTbcoLeEO/yed+2KwKgk1ucOYZxMR 4rdnhK/ENTXtuvVkOw32VDD6rF7rnVrcuE4FpA6yP0W7aY0EjKgvvrmXplPaHoZ3h+ p+RFTPzt/fzhQ== Message-ID: <5732e382-3ebb-43e2-8aaa-4729387cea5e@kernel.org> Date: Fri, 20 Mar 2026 11:08:50 +0100 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 1/4] mm/mprotect: encourage inlining with __always_inline To: Pedro Falcato , Lorenzo Stoakes Cc: Andrew Morton , "Liam R. Howlett" , Vlastimil Babka , Jann Horn , Dev Jain , Luke Yang , jhladky@redhat.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20260319183108.1105090-1-pfalcato@suse.de> <20260319183108.1105090-2-pfalcato@suse.de> <9943a6ad-9c85-439c-ad9e-39a694a29147@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzS5EYXZpZCBIaWxk ZW5icmFuZCAoQ3VycmVudCkgPGRhdmlkQGtlcm5lbC5vcmc+wsGQBBMBCAA6AhsDBQkmWAik AgsJBBUKCQgCFgICHgUCF4AWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaYJt/AIZAQAKCRBN 3hD3AP+DWriiD/9BLGEKG+N8L2AXhikJg6YmXom9ytRwPqDgpHpVg2xdhopoWdMRXjzOrIKD g4LSnFaKneQD0hZhoArEeamG5tyo32xoRsPwkbpIzL0OKSZ8G6mVbFGpjmyDLQCAxteXCLXz ZI0VbsuJKelYnKcXWOIndOrNRvE5eoOfTt2XfBnAapxMYY2IsV+qaUXlO63GgfIOg8RBaj7x 3NxkI3rV0SHhI4GU9K6jCvGghxeS1QX6L/XI9mfAYaIwGy5B68kF26piAVYv/QZDEVIpo3t7 /fjSpxKT8plJH6rhhR0epy8dWRHk3qT5tk2P85twasdloWtkMZ7FsCJRKWscm1BLpsDn6EQ4 jeMHECiY9kGKKi8dQpv3FRyo2QApZ49NNDbwcR0ZndK0XFo15iH708H5Qja/8TuXCwnPWAcJ DQoNIDFyaxe26Rx3ZwUkRALa3iPcVjE0//TrQ4KnFf+lMBSrS33xDDBfevW9+Dk6IISmDH1R HFq2jpkN+FX/PE8eVhV68B2DsAPZ5rUwyCKUXPTJ/irrCCmAAb5Jpv11S7hUSpqtM/6oVESC 3z/7CzrVtRODzLtNgV4r5EI+wAv/3PgJLlMwgJM90Fb3CB2IgbxhjvmB1WNdvXACVydx55V7 LPPKodSTF29rlnQAf9HLgCphuuSrrPn5VQDaYZl4N/7zc2wcWM7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 3/20/26 10:59, Pedro Falcato wrote: > On Thu, Mar 19, 2026 at 10:28:47PM +0100, David Hildenbrand (Arm) wrote: >> On 3/19/26 19:31, Pedro Falcato wrote: >>> Encourage the compiler to inline batch PTE logic and resolve constant >>> branches by adding __always_inline strategically. >>> >>> Signed-off-by: Pedro Falcato >>> --- >>> mm/mprotect.c | 10 +++++----- >>> 1 file changed, 5 insertions(+), 5 deletions(-) >>> >>> diff --git a/mm/mprotect.c b/mm/mprotect.c >>> index 9681f055b9fc..1bd0d4aa07c2 100644 >>> --- a/mm/mprotect.c >>> +++ b/mm/mprotect.c >>> @@ -103,7 +103,7 @@ bool can_change_pte_writable(struct vm_area_struct *vma, unsigned long addr, >>> return can_change_shared_pte_writable(vma, pte); >>> } >>> >>> -static int mprotect_folio_pte_batch(struct folio *folio, pte_t *ptep, >>> +static __always_inline int mprotect_folio_pte_batch(struct folio *folio, pte_t *ptep, >>> pte_t pte, int max_nr_ptes, fpb_t flags) >>> { >>> /* No underlying folio, so cannot batch */ >>> @@ -117,9 +117,9 @@ static int mprotect_folio_pte_batch(struct folio *folio, pte_t *ptep, >>> } >>> >>> /* Set nr_ptes number of ptes, starting from idx */ >>> -static void prot_commit_flush_ptes(struct vm_area_struct *vma, unsigned long addr, >>> - pte_t *ptep, pte_t oldpte, pte_t ptent, int nr_ptes, >>> - int idx, bool set_write, struct mmu_gather *tlb) >>> +static __always_inline void prot_commit_flush_ptes(struct vm_area_struct *vma, >>> + unsigned long addr, pte_t *ptep, pte_t oldpte, pte_t ptent, >>> + int nr_ptes, int idx, bool set_write, struct mmu_gather *tlb) >>> { >>> /* >>> * Advance the position in the batch by idx; note that if idx > 0, >>> @@ -169,7 +169,7 @@ static int page_anon_exclusive_sub_batch(int start_idx, int max_len, >>> * pte of the batch. Therefore, we must individually check all pages and >>> * retrieve sub-batches. >>> */ >>> -static void commit_anon_folio_batch(struct vm_area_struct *vma, >>> +static __always_inline void commit_anon_folio_batch(struct vm_area_struct *vma, >>> struct folio *folio, struct page *first_page, unsigned long addr, pte_t *ptep, >>> pte_t oldpte, pte_t ptent, int nr_ptes, struct mmu_gather *tlb) >>> { >> >> From my micro-optimization work on zapping and fork, I learned that >> these batching functions are best optimized for order-0 page by >> explicitly calling them from the code with "nr_ptes == 1" and then >> force-inlining them. nr_ptes and all loops will essentially be optimized >> out. >> >> With no such explicit constants, is there really a real benefit to be >> had here? > > Per my measurements, I could measure a real speedup here. Of course things > may heavily depend on the microarchitecture you use. I want to note that > these three functions are part of the hot loop and thus we definitely want > them inlined. Particularly if we start special-casing stuff. You can cut > down _a lot_ of code if you simply tell it "yeah don't bother you're looking > at 1 pte only". That's why I think this change is a lot more valuable when squashing patch #4. -- Cheers, David