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 BFF8822619; Wed, 31 Jan 2024 11:16:35 +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=1706699798; cv=none; b=VAd9Wg9llQePdM2DVCz2k1LB8kPIj1ucsCUJikfupOalEfea+1B9YgbOrX7kVbUFJ7dnrxYqs9Di+qAHw1zrJl/+Lwnctoj/T0YGA+ar0+YDZ09ubOf9V6IiPn6Ga20TnhPEHQCr8CMudbaubVZWG/fqkh3NAVPaQSzegjQhcYA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1706699798; c=relaxed/simple; bh=ya2D7JlmbHhu2JlG/LgQfIA57MBp5NTjnz6Qi58XIqs=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=AHmwgRghN23hXJCV/fskW1k3uwxTDAfJEEx/QigUUFqtBf7jIqGSiilys57HV/AEVnMiOpOsaOuyEgjdv2mLamDj64cZxeKx5NVf3y912ByODEJG1WfaMdIEoKGFPGf2wU33okgsWylK/bpYQQsEVj6f0r5+ExdyzuywT+IDaL0= 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 1741CDA7; Wed, 31 Jan 2024 03:17:18 -0800 (PST) Received: from [10.57.79.60] (unknown [10.57.79.60]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id CCBC23F762; Wed, 31 Jan 2024 03:16:28 -0800 (PST) Message-ID: <57eb82c7-4816-42a2-b5ab-cc221e289b21@arm.com> Date: Wed, 31 Jan 2024 11:16:26 +0000 Precedence: bulk X-Mailing-List: linux-s390@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 00/15] mm/memory: optimize fork() with PTE-mapped THP Content-Language: en-GB To: David Hildenbrand , linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, Andrew Morton , Matthew Wilcox , Russell King , Catalin Marinas , Will Deacon , Dinh Nguyen , Michael Ellerman , Nicholas Piggin , Christophe Leroy , "Aneesh Kumar K.V" , "Naveen N. Rao" , Paul Walmsley , Palmer Dabbelt , Albert Ou , Alexander Gordeev , Gerald Schaefer , Heiko Carstens , Vasily Gorbik , Christian Borntraeger , Sven Schnelle , "David S. Miller" , linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org, sparclinux@vger.kernel.org References: <20240129124649.189745-1-david@redhat.com> From: Ryan Roberts In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 31/01/2024 11:06, David Hildenbrand wrote: > On 31.01.24 11:43, Ryan Roberts wrote: >> On 29/01/2024 12:46, David Hildenbrand wrote: >>> Now that the rmap overhaul[1] is upstream that provides a clean interface >>> for rmap batching, let's implement PTE batching during fork when processing >>> PTE-mapped THPs. >>> >>> This series is partially based on Ryan's previous work[2] to implement >>> cont-pte support on arm64, but its a complete rewrite based on [1] to >>> optimize all architectures independent of any such PTE bits, and to >>> use the new rmap batching functions that simplify the code and prepare >>> for further rmap accounting changes. >>> >>> We collect consecutive PTEs that map consecutive pages of the same large >>> folio, making sure that the other PTE bits are compatible, and (a) adjust >>> the refcount only once per batch, (b) call rmap handling functions only >>> once per batch and (c) perform batch PTE setting/updates. >>> >>> While this series should be beneficial for adding cont-pte support on >>> ARM64[2], it's one of the requirements for maintaining a total mapcount[3] >>> for large folios with minimal added overhead and further changes[4] that >>> build up on top of the total mapcount. >>> >>> Independent of all that, this series results in a speedup during fork with >>> PTE-mapped THP, which is the default with THPs that are smaller than a PMD >>> (for example, 16KiB to 1024KiB mTHPs for anonymous memory[5]). >>> >>> On an Intel Xeon Silver 4210R CPU, fork'ing with 1GiB of PTE-mapped folios >>> of the same size (stddev < 1%) results in the following runtimes >>> for fork() (shorter is better): >>> >>> Folio Size | v6.8-rc1 |      New | Change >>> ------------------------------------------ >>>        4KiB | 0.014328 | 0.014035 |   - 2% >>>       16KiB | 0.014263 | 0.01196  |   -16% >>>       32KiB | 0.014334 | 0.01094  |   -24% >>>       64KiB | 0.014046 | 0.010444 |   -26% >>>      128KiB | 0.014011 | 0.010063 |   -28% >>>      256KiB | 0.013993 | 0.009938 |   -29% >>>      512KiB | 0.013983 | 0.00985  |   -30% >>>     1024KiB | 0.013986 | 0.00982  |   -30% >>>     2048KiB | 0.014305 | 0.010076 |   -30% >> >> Just a heads up that I'm seeing some strange results on Apple M2. Fork for >> order-0 is seemingly costing ~17% more. I'm using GCC 13.2 and was pretty sure I >> didn't see this problem with version 1; although that was on a different >> baseline and I've thrown the numbers away so will rerun and try to debug this. >> > > So far, on my x86 tests (Intel, AMD EPYC), I was not able to observe this. > fork() for order-0 was consistently effectively unchanged. Do you observe that > on other ARM systems as well? Nope; running the exact same kernel binary and user space on Altra, I see sensible numbers; fork order-0: -1.3% fork order-9: -7.6% dontneed order-0: -0.5% dontneed order-9: 0.1% munmap order-0: 0.0% munmap order-9: -67.9% So I guess some pipelining issue that causes the M2 to stall more? > > >> | kernel      |   mean_rel |   std_rel | >> |:------------|-----------:|----------:| >> | mm-unstable |       0.0% |      1.1% | >> | patch 1     |      -2.3% |      1.3% | >> | patch 10    |      -2.9% |      2.7% | >> | patch 11    |      13.5% |      0.5% | >> | patch 12    |      15.2% |      1.2% | >> | patch 13    |      18.2% |      0.7% | >> | patch 14    |      20.5% |      1.0% | >> | patch 15    |      17.1% |      1.6% | >> | patch 15    |      16.7% |      0.8% | >> >> fork for order-9 is looking good (-20%), and for the zap series, munmap is >> looking good, but dontneed is looking poor for both order-0 and 9. But one thing >> at a time... let's concentrate on fork order-0 first. > > munmap and dontneed end up calling the exact same call paths. So a big > performance difference is rather surprising and might indicate something else. > > (I think I told you that I was running in some kind of VMA merging problem where > one would suddenly get with my benchmark 1 VMA per page. The new benchmark below > works around that, but I am not sure if that was fixed in the meantime) > > VMA merging can of course explain a big difference in fork and munmap vs. > dontneed times, especially when comparing different code base where that VMA > merging behavior was different. > >> >> Note that I'm still using the "old" benchmark code. Could you resend me the link >> to the new code? Although I don't think there should be any effect for order-0 >> anyway, if I understood your changes correctly? > > This is the combined one (small and large PTEs): > > https://gitlab.com/davidhildenbrand/scratchspace/-/raw/main/pte-mapped-folio-benchmarks.c?inline=false I'll have a go with this. >