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 AFA5A6E2A1; Wed, 31 Jan 2024 10:43:32 +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=1706697815; cv=none; b=o8ovhScSbp3JdTcp36XDgguF5wMTAzoQfYhv+zmPpGWSPqU9M7MmGAc50952fuJPvCJnWxO1TML+Ie3BZ95Mfnn1dn02DNhUx5NsoXGbPz83jSJ90AC3i71Q0FXE93m4B3OHRIEzMpYrVDhj+IySDTa2WNuCmezUf4MciLma0zg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1706697815; c=relaxed/simple; bh=zZQPK++Cu/dd94eonPI6nYAV7fC8migqP2H6ZM6nUp0=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=NiVgpY52ymniFa38xhl0/b/sfdrmrNTMXaWGSE+pgM3cd6h/+yEpvR3SP7EAGBEz1U2W2GeDeDnmxLDrN4nSi9xmgR2bjxrPprW9qgkFDsKL0g4Vkjh4FlJWjkogv5D84wv9kx9qY41tNQgohZH0/Nosl/IYTR+A3/qik66Hmhw= 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 61E34DA7; Wed, 31 Jan 2024 02:44:15 -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 A2F0D3F5A1; Wed, 31 Jan 2024 02:43:24 -0800 (PST) Message-ID: Date: Wed, 31 Jan 2024 10:43:22 +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: <20240129124649.189745-1-david@redhat.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit 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. | 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. 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? > > Note that these numbers are even better than the ones from v1 (verified > over multiple reboots), even though there were only minimal code changes. > Well, I removed a pte_mkclean() call for anon folios, maybe that also > plays a role. > > But my experience is that fork() is extremely sensitive to code size, > inlining, ... so I suspect we'll see on other architectures rather a change > of -20% instead of -30%, and it will be easy to "lose" some of that speedup > in the future by subtle code changes. > > Next up is PTE batching when unmapping. Only tested on x86-64. > Compile-tested on most other architectures. > > v2 -> v3: > * Rebased on mm-unstable > * Picked up RB's > * Updated documentation of wrprotect_ptes(). > > v1 -> v2: > * "arm64/mm: Make set_ptes() robust when OAs cross 48-bit boundary" > -> Added patch from Ryan > * "arm/pgtable: define PFN_PTE_SHIFT" > -> Removed the arm64 bits > * "mm/pgtable: make pte_next_pfn() independent of set_ptes()" > * "arm/mm: use pte_next_pfn() in set_ptes()" > * "powerpc/mm: use pte_next_pfn() in set_ptes()" > -> Added to use pte_next_pfn() in some arch set_ptes() implementations > I tried to make use of pte_next_pfn() also in the others, but it's > not trivial because the other archs implement set_ptes() in their > asm/pgtable.h. Future work. > * "mm/memory: factor out copying the actual PTE in copy_present_pte()" > -> Move common folio_get() out of if/else > * "mm/memory: optimize fork() with PTE-mapped THP" > -> Add doc for wrprotect_ptes > -> Extend description to mention handling of pinned folios > -> Move common folio_ref_add() out of if/else > * "mm/memory: ignore dirty/accessed/soft-dirty bits in folio_pte_batch()" > -> Be more conservative with dirt/soft-dirty, let the caller specify > using flags > > [1] https://lkml.kernel.org/r/20231220224504.646757-1-david@redhat.com > [2] https://lkml.kernel.org/r/20231218105100.172635-1-ryan.roberts@arm.com > [3] https://lkml.kernel.org/r/20230809083256.699513-1-david@redhat.com > [4] https://lkml.kernel.org/r/20231124132626.235350-1-david@redhat.com > [5] https://lkml.kernel.org/r/20231207161211.2374093-1-ryan.roberts@arm.com > > Cc: Andrew Morton > Cc: Matthew Wilcox (Oracle) > Cc: Ryan Roberts > Cc: Russell King > Cc: Catalin Marinas > Cc: Will Deacon > Cc: Dinh Nguyen > Cc: Michael Ellerman > Cc: Nicholas Piggin > Cc: Christophe Leroy > Cc: "Aneesh Kumar K.V" > Cc: "Naveen N. Rao" > Cc: Paul Walmsley > Cc: Palmer Dabbelt > Cc: Albert Ou > Cc: Alexander Gordeev > Cc: Gerald Schaefer > Cc: Heiko Carstens > Cc: Vasily Gorbik > Cc: Christian Borntraeger > Cc: Sven Schnelle > Cc: "David S. Miller" > Cc: linux-arm-kernel@lists.infradead.org > Cc: linuxppc-dev@lists.ozlabs.org > Cc: linux-riscv@lists.infradead.org > Cc: linux-s390@vger.kernel.org > Cc: sparclinux@vger.kernel.org > > --- > > Andrew asked for a resend based on latest mm-unstable. I am sending this > out earlier than I would usually have sent out the next version, so we can > pull it into mm-unstable again now that v1 was dropped. > > David Hildenbrand (14): > arm/pgtable: define PFN_PTE_SHIFT > nios2/pgtable: define PFN_PTE_SHIFT > powerpc/pgtable: define PFN_PTE_SHIFT > riscv/pgtable: define PFN_PTE_SHIFT > s390/pgtable: define PFN_PTE_SHIFT > sparc/pgtable: define PFN_PTE_SHIFT > mm/pgtable: make pte_next_pfn() independent of set_ptes() > arm/mm: use pte_next_pfn() in set_ptes() > powerpc/mm: use pte_next_pfn() in set_ptes() > mm/memory: factor out copying the actual PTE in copy_present_pte() > mm/memory: pass PTE to copy_present_pte() > mm/memory: optimize fork() with PTE-mapped THP > mm/memory: ignore dirty/accessed/soft-dirty bits in folio_pte_batch() > mm/memory: ignore writable bit in folio_pte_batch() > > Ryan Roberts (1): > arm64/mm: Make set_ptes() robust when OAs cross 48-bit boundary > > arch/arm/include/asm/pgtable.h | 2 + > arch/arm/mm/mmu.c | 2 +- > arch/arm64/include/asm/pgtable.h | 28 ++-- > arch/nios2/include/asm/pgtable.h | 2 + > arch/powerpc/include/asm/pgtable.h | 2 + > arch/powerpc/mm/pgtable.c | 5 +- > arch/riscv/include/asm/pgtable.h | 2 + > arch/s390/include/asm/pgtable.h | 2 + > arch/sparc/include/asm/pgtable_64.h | 2 + > include/linux/pgtable.h | 33 ++++- > mm/memory.c | 212 ++++++++++++++++++++++------ > 11 files changed, 229 insertions(+), 63 deletions(-) > > > base-commit: d162e170f1181b4305494843e1976584ddf2b72e