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 C2F5B340A6B for ; Mon, 30 Mar 2026 15:16:55 +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=1774883815; cv=none; b=jedjXQZoKqe1U3b5HmE1nrSZZ9j1yMe232erTjlA8U2cz3S8DTgLLlgNciZojAGGQOukYaMYVuaKb1JhDvZGM8KR/gxI8vn1lkoDzUVZD6/FDV0vsN3gKB92g+2/JQy+lhF3SOxzxcuA80k2Jh0xuzdrVQeKDec25S0f3TCXykg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774883815; c=relaxed/simple; bh=qRggfUYSMFyYosinS8dQnA8OwjJgvfCqMgEcNyPBSZw=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=WtqfMR7+7X7SitkUA4ti+Czuear9DMR8gjDF+qgboS7FTV3Lt8poCyfHxTYCLMVM5P2YbILkSw149s/qnDNw3D/iQb7Hw5A1xq7GMIMSd8rZYY4IZSt1eoiVF47EtZ/UXsa7kTinjDzfUXIHwXj0wO43/CaBqZsdLWyjSEf3C+g= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=M5YLUHTP; 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="M5YLUHTP" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3EA90C19423; Mon, 30 Mar 2026 15:16:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1774883815; bh=qRggfUYSMFyYosinS8dQnA8OwjJgvfCqMgEcNyPBSZw=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=M5YLUHTPR0Zr87dAPlgooj2AUqUS4ilSBIlOIUk0+shH9LCpc7hJkNsS35FbbHJlg 11vvFt94hMJ0rRBfYkrqplKmfFKFHCCNmihD9Bk9UIqm56Fpv2EnMcH7I48X9RjAT+ 8ZFRoQ37DHKHXECdFw/qGzfjceMRulnKYivXfc7JiapiNgMiJWfJjV6Z/yWzR9vjgp ErfxVQMsRZGnnfxA9E0ouHFGc48hL/2CZlxqVq50cXWck38aEngkPDXDhrUlVxlsv/ GlTfmXo8BdNIPudQx+UU2vyfXLtH8ozNbDrt+ume6rWD1XtYOUdDgFOikImyYIWRMu W2HwMKUPHx5Xw== Message-ID: Date: Mon, 30 Mar 2026 17:16:51 +0200 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 v2 2/2] mm/mprotect: special-case small folios when applying write permissions To: Pedro Falcato Cc: Andrew Morton , "Liam R. Howlett" , Lorenzo Stoakes , Vlastimil Babka , Jann Horn , Dev Jain , Luke Yang , jhladky@redhat.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20260324154342.156640-1-pfalcato@suse.de> <20260324154342.156640-3-pfalcato@suse.de> 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 3/25/26 12:37, Pedro Falcato wrote: > On Tue, Mar 24, 2026 at 09:18:42PM +0100, David Hildenbrand (Arm) wrote: >> On 3/24/26 16:43, Pedro Falcato wrote: >>> The common order-0 case is important enough to want its own branch, and >>> avoids the hairy, large loop logic that the CPU does not seem to handle >>> particularly well. >>> >>> While at it, encourage the compiler to inline batch PTE logic and resolve >>> constant branches by adding __always_inline strategically. >>> >>> Reviewed-by: Lorenzo Stoakes (Oracle) >>> Signed-off-by: Pedro Falcato >>> --- >>> mm/mprotect.c | 17 ++++++++++++----- >>> 1 file changed, 12 insertions(+), 5 deletions(-) >>> >>> diff --git a/mm/mprotect.c b/mm/mprotect.c >>> index 2eaf862e5734..2fda26107066 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) >>> { >>> @@ -177,6 +177,13 @@ static void commit_anon_folio_batch(struct vm_area_struct *vma, >>> int sub_batch_idx = 0; >>> int len; >>> >>> + /* Optimize for the common order-0 case. */ >>> + if (likely(nr_ptes == 1)) { >>> + prot_commit_flush_ptes(vma, addr, ptep, oldpte, ptent, 1, >>> + 0, PageAnonExclusive(first_page), tlb); >> >> To optimize that one, inlining prot_commit_flush_ptes() would be >> sufficient. Does inlining the other two really help? I don't think we >> can optimize out loops etc. for them? > > Well, I'm getting meaningful (smaller) wins from adding those > __always_inline's. (and I also get a small win for __always_inline on > set_write_prot_commit_flush_ptes, but I didn't realize that until now). > >> >> I would have thought that specializing on nr_ptes==0 on an even higher >> level--where we call >> set_write_prot_commit_flush_ptes/prot_commit_flush_ptes() would allow >> for optimizing the loops entirely for nr_ptes==0? > > That could also work, but then set_write_prot_commit_flush_ptes (holy cow > what a long name) would definitely need inlining. And might be a little uglier > overall. Right. The idea is that you __always__inline any code that has PTE loops, such that all loops for nr_pages == 1 gets optimized out. We do that for zap and fork logic. > > This is the part where having data points other than my giga-fast-giga-powerful > zen5 could prove handy :/ I just recently lost access to my reliably, well tunes, system ... Is it just the following benchmark? https://gist.github.com/heatd/1450d273005aba91fa5744f44dfcd933 ? I can easily extending https://gitlab.com/davidhildenbrand/scratchspace/-/blob/main/pte-mapped-folio-benchmarks.c to have an "mprotect" mode. I had that in the past bit discarded it. Then, we can easily measure the effect on various folio sizes when mprotect'ing a larger memory area. With order-0 we can then benchmark small folios exclusively. -- Cheers, David