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 B1BC83446DF for ; Tue, 23 Dec 2025 10:11:40 +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=1766484700; cv=none; b=rAedbaKiVPItwbzSmwpcBLjgSNREVBlH/FlfWSc3lAxtyj3UmHGFkFPfcrnO+FwFe3J35cKa+Ovp+vCwGBilIF6Y6loQBp5QtfeiKW+eOhdWjIKdm0SABhmfwzT9QhX0lCZZ4TmTTbTx6jUK/Bh1bKo1zwtzoeUM2Su/bjuNbxM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1766484700; c=relaxed/simple; bh=lW5sFlnkDGCk5rH+BKM70TDQJ6o2G2rSA6rdfTk92Ec=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=s7BUmHtZMjTMLc7sk3rZ9HHzY2Of4fgWhrGFqeR2swr6lsCjE7j1uSuxaMRTBZsivx1IT5CsKMgFcDS4g5YUV7wM9wZyZnTy5SAHWIm1JG00SDTAWMiGK/7NsPt2CSyXA4i9MVIKBXI657q48VPhpzQN0EVoqv7CND97dw/5lXc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=qfaXd6LV; 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="qfaXd6LV" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7CF5EC113D0; Tue, 23 Dec 2025 10:11:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1766484700; bh=lW5sFlnkDGCk5rH+BKM70TDQJ6o2G2rSA6rdfTk92Ec=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=qfaXd6LV/97eGac5d66TW/vMC1F2uEZNncbDZ1FyoriP7J98H5Nybs4slrobcIJ7J dlTKbCcLUsGqSrz8sp0FcXG71yBQf+mVVvZm0MJ/l0yNuHUR8wK1AeCUb4NlXGXmAw biqiCyn7eokdhMsAt9PKTfNdGdoYNj3x0bSYJQY04sZLDvUoqUEYKaOhwBeczBGB3a 3I5xTomu+vzAAtA6tNhUlpJOibM0RRYr1LBQqxWFxFHUfKf0GMo7H3tcDDwNbcVQlT CPmV9BX11DGezT9ng0FMOKbtbUTvPDE27/nkKJsJwwX8MMxsGjlZdF4PEd+PRIWOBg QieAjEaN/ZE6w== Message-ID: <4e3ff85e-2c8c-489e-92b4-088189eed63b@kernel.org> Date: Tue, 23 Dec 2025 11:11:32 +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 v10 8/8] mm: folio_zero_user: cache neighbouring pages To: Ankur Arora Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, x86@kernel.org, akpm@linux-foundation.org, bp@alien8.de, dave.hansen@linux.intel.com, hpa@zytor.com, mingo@redhat.com, mjguzik@gmail.com, luto@kernel.org, peterz@infradead.org, tglx@linutronix.de, willy@infradead.org, raghavendra.kt@amd.com, chleroy@kernel.org, ioworker0@gmail.com, boris.ostrovsky@oracle.com, konrad.wilk@oracle.com References: <20251215204922.475324-1-ankur.a.arora@oracle.com> <20251215204922.475324-9-ankur.a.arora@oracle.com> <874ipnwlky.fsf@oracle.com> <87jyyjv5zy.fsf@oracle.com> From: "David Hildenbrand (Red Hat)" Content-Language: en-US In-Reply-To: <87jyyjv5zy.fsf@oracle.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 12/18/25 22:23, Ankur Arora wrote: > > Ankur Arora writes: > >> David Hildenbrand (Red Hat) writes: >> >>> On 12/15/25 21:49, Ankur Arora wrote: >>>> folio_zero_user() does straight zeroing without caring about >>>> temporal locality for caches. >>>> This replaced commit c6ddfb6c5890 ("mm, clear_huge_page: move order >>>> algorithm into a separate function") where we cleared a page at a >>>> time converging to the faulting page from the left and the right. >>>> To retain limited temporal locality, split the clearing in three >>>> parts: the faulting page and its immediate neighbourhood, and, the >>>> remaining regions on the left and the right. The local neighbourhood >>>> will be cleared last. >>>> Do this only when zeroing small folios (< MAX_ORDER_NR_PAGES) since >>>> there isn't much expectation of cache locality for large folios. >>>> Performance >>>> === >>>> AMD Genoa (EPYC 9J14, cpus=2 sockets * 96 cores * 2 threads, >>>> memory=2.2 TB, L1d= 16K/thread, L2=512K/thread, L3=2MB/thread) >>>> anon-w-seq (vm-scalability): >>>> stime utime >>>> page-at-a-time 1654.63 ( +- 3.84% ) 811.00 ( +- 3.84% ) >>>> contiguous clearing 1602.86 ( +- 3.00% ) 970.75 ( +- 4.68% ) >>>> neighbourhood-last 1630.32 ( +- 2.73% ) 886.37 ( +- 5.19% ) >>>> Both stime and utime respond in expected ways. stime drops for both >>>> contiguous clearing (-3.14%) and neighbourhood-last (-1.46%) >>>> approaches. However, utime increases for both contiguous clearing >>>> (+19.7%) and neighbourhood-last (+9.28%). >>>> In part this is because anon-w-seq runs with 384 processes zeroing >>>> anonymously mapped memory which they then access sequentially. As >>>> such this is likely an uncommon pattern where the memory bandwidth >>>> is saturated while also being cache limited because we access the >>>> entire region. >>>> Kernel make workload (make -j 12 bzImage): >>>> stime utime >>>> page-at-a-time 138.16 ( +- 0.31% ) 1015.11 ( +- 0.05% ) >>>> contiguous clearing 133.42 ( +- 0.90% ) 1013.49 ( +- 0.05% ) >>>> neighbourhood-last 131.20 ( +- 0.76% ) 1011.36 ( +- 0.07% ) >>>> For make the utime stays relatively flat with an up to 4.9% improvement >>>> in the stime. >>> >>> Nice evaluation! >>> >>>> Signed-off-by: Ankur Arora >>>> Reviewed-by: Raghavendra K T >>>> Tested-by: Raghavendra K T >>>> --- >>>> mm/memory.c | 44 ++++++++++++++++++++++++++++++++++++++++++-- >>>> 1 file changed, 42 insertions(+), 2 deletions(-) >>>> diff --git a/mm/memory.c b/mm/memory.c >>>> index 974c48db6089..d22348b95227 100644 >>>> --- a/mm/memory.c >>>> +++ b/mm/memory.c >>>> @@ -7268,13 +7268,53 @@ static void clear_contig_highpages(struct page *page, unsigned long addr, >>>> * @addr_hint: The address accessed by the user or the base address. >>>> * >>>> * Uses architectural support to clear page ranges. >>>> + * >>>> + * Clearing of small folios (< MAX_ORDER_NR_PAGES) is split in three parts: >>>> + * pages in the immediate locality of the faulting page, and its left, right >>>> + * regions; the local neighbourhood is cleared last in order to keep cache >>>> + * lines of the faulting region hot. >>>> + * >>>> + * For larger folios we assume that there is no expectation of cache locality >>>> + * and just do a straight zero. >>> >>> Just wondering: why not do the same thing here as well? Probably shouldn't hurt >>> and would get rid of some code? >> >> That's a good point. With only a three way split, there's no reason to >> treat large folios specially. > > A bit more on this: this change makes sense but I'll retain the current > split between patches-7, 8. > > Where patch-7, is used to justify using contiguous clearing (and the > choice of value for PROCESS_PAGES_NON_PREEMPT_BATCH), unit based on > preemption model etc and patch-8, for the neighbourhood optimization. > >>>> */ >>>> void folio_zero_user(struct folio *folio, unsigned long addr_hint) >>>> { >>>> unsigned long base_addr = ALIGN_DOWN(addr_hint, folio_size(folio)); >>> >>> While at it you could turn that const as well. >> >> Ack. >> >>>> + const long fault_idx = (addr_hint - base_addr) / PAGE_SIZE; >>>> + const struct range pg = DEFINE_RANGE(0, folio_nr_pages(folio) - 1); >>>> + const int width = 2; /* number of pages cleared last on either side */ >>> >>> Is "width" really the right terminology? (the way you describe it, it's more >>> like diameter?) >> >> I like diameter. Will make that a define. > > I'll make that radius since that's how I'm using it. All makes sense to me. -- Cheers David