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 62ED6E573 for ; Thu, 2 Apr 2026 00:09:32 +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=1775088572; cv=none; b=kFowE9jXN+/hLxEXlxIhdSF+CrtUVNR9bHK3yRPkImwDx1jdtPTecZFQWeefTLXNYN3kBIDK2RlaBbgF9ScdkiSvzSxbddweoWEFjmubcU8qUjsjj7GPP6fAjFQqBq4/NjvdYUD4l5ykQRYduVnzqIsYmfpsu80n6NKuGekoMWg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775088572; c=relaxed/simple; bh=dkAtgDLSBaxNr5vlZELUNXtYvuqifZY6JTWaqhRVgv8=; h=Date:From:To:Cc:Subject:Message-Id:In-Reply-To:References: Mime-Version:Content-Type; b=ihua8pcRO6LEbQyPFAAk6kDENo7QAc+gsXBhYPVWEPJfVzuQ1xYMj2kbyBXNI6swAsn/PDW2CLCV0witSvfFLq97iajmVGNcH+LQTc90wbA92+XZDHxX6o7YJ7ZwVfIiZ2p5R16y9R+GJ5dgIHcaF0Bd1jvjsougYjpD7c1KBRo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b=1WJ8RFiQ; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="1WJ8RFiQ" Received: by smtp.kernel.org (Postfix) with ESMTPSA id BBD2CC4CEF7; Thu, 2 Apr 2026 00:09:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1775088572; bh=dkAtgDLSBaxNr5vlZELUNXtYvuqifZY6JTWaqhRVgv8=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=1WJ8RFiQxomXlhtkeMx4OumY070hPRb9rh/7m56LYt6iVWvhEGUyg2LUl2uF2et1u r0kBOvehREBh1C9w7966A64zWRSKJYETLghEhiDoKz6m9XKjOXI+CFLxk2yCMvR6M8 KHZJiOaoxC2P8ECWIqIky/JiDAfGCs1lcOF+xQ9s= Date: Wed, 1 Apr 2026 17:09:31 -0700 From: Andrew Morton To: "David Hildenbrand (Arm)" Cc: Pedro Falcato , "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 Subject: Re: [PATCH v2 2/2] mm/mprotect: special-case small folios when applying write permissions Message-Id: <20260401170931.9e455bbf679792b039d9770a@linux-foundation.org> In-Reply-To: References: <20260324154342.156640-1-pfalcato@suse.de> <20260324154342.156640-3-pfalcato@suse.de> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Mon, 30 Mar 2026 17:16:51 +0200 "David Hildenbrand (Arm)" wrote: > > 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. It sounds like this is all possible future work? We have Lorenzo's R-b on this [2/2]. I'm reading this discussion as "upstream both"? --- a/mm/mprotect.c~mm-mprotect-special-case-small-folios-when-applying-write-permissions +++ a/mm/mprotect.c @@ -103,7 +103,7 @@ bool can_change_pte_writable(struct vm_a 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(stru } /* 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 * 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(stru 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); + return; + } + while (nr_ptes) { expected_anon_exclusive = PageAnonExclusive(first_page + sub_batch_idx); len = page_anon_exclusive_sub_batch(sub_batch_idx, nr_ptes, _