From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 0EFC13A4523; Fri, 2 Oct 2026 12:08:16 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790942898; cv=none; b=GQrsALbEbi+wphPOJcGFcWeG8vkvYLki8pWljjhSuj62SUn7UzzZcLNpMc35emXLvvThb3dZ2V+nG7b9rNQY6orj+oWeN8FV9yHx+pud1qGu3Kk1MYTX6zbDkt1qU2pS7FX1DguEQDucp4XLJFCe9A0pGjg9JIRRWpX+4Q7kbws= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790942898; c=relaxed/simple; bh=c8hTcCvyfn58VxOulb9D2sz8nvlf4KjPQ2FsvNwNWvs=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=rVFF203p1yqJ4Kv6NqbBv0MdcmI5Y0rtUcuzeKTUItH79z0VSNrMqdbt9lqpWZE4BrL2TL9iT13duiu1NMIty1aL4EZkDIRD6iRAc7Qwwrxp0fyHOoUSzygc6eOCmJYgNqEOoblkTOufzMYpKsaisK/V7Rba9hGK+jW070GF/Xs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Qhdt8Ng3; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="Qhdt8Ng3" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 34F1A1F000FF; Fri, 2 Oct 2026 12:08:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1790942896; bh=JUHbJ2wYZgiOnAwObcV975WzRcpiwXyJLliBcLauNuc=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=Qhdt8Ng3BHQCcF6XLWHIK3XVYvyTGIo1LuSR7+HBC/swZH28L6G+DvlB3cOOWvOkD DtKXltQK+JBlcV2quCjFoDeV1lxUtJxiYvwuR2S3Cu+lV0QRny8RkXGRa3BYKgZZVf QfiSVRfw/N0RKmNfxM26bk4ETWD50h7YjBF7ZKlHmmULShnii9lQ6GKBjHlXzOaI46 8pUznw1iNoCz3QjbvvnKwcYB6/mMYg+AKhOxJk16GJsKwJmwFOKSWRnP/w3R4SGnjD Cj6G+xnl35BKOtIJTvIE/GsBbICb7v9QQQIrMYPAyxElTig5783sZb4vhxN7jKeBBb V4qHHVzKo1bCg== Message-ID: <54a7252b-ab2d-4230-9a1a-d4d1b670b7c8@kernel.org> Date: Fri, 2 Oct 2026 12:15:10 +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 v3 0/9] Optimize anonymous swapbacked large folio unmapping To: Dev Jain , akpm@linux-foundation.org, ljs@kernel.org, hughd@google.com, chrisl@kernel.org, kasong@tencent.com, davem@davemloft.net, andreas@gaisler.com Cc: riel@surriel.com, liam@infradead.org, vbabka@kernel.org, harry@kernel.org, jannh@google.com, lance.yang@linux.dev, baolin.wang@linux.alibaba.com, shikemeng@huaweicloud.com, nphamcs@gmail.com, baoquan.he@linux.dev, baohua@kernel.org, youngjun.park@lge.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, pfalcato@suse.de, jgg@ziepe.ca, thuth@redhat.com, sparclinux@vger.kernel.org, ryan.roberts@arm.com, anshuman.khandual@arm.com References: <20260924131106.1730494-1-dev.jain@arm.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 9/24/26 15:09, Dev Jain wrote: > Speed up unmapping of anonymous swapbacked large folios by clearing > the ptes, and setting swap ptes, in one go. > > The following benchmark (stolen from Barry) is used to measure the > time taken to swapout 256M worth of memory backed by 64K large folios: > > #define _GNU_SOURCE > #include > #include > #include > #include > #include > #include > #include > > #define SIZE_MB 256 > #define SIZE_BYTES (SIZE_MB * 1024 * 1024) > > int main() { > void *addr = mmap(NULL, SIZE_BYTES, PROT_READ | PROT_WRITE, > MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); > if (addr == MAP_FAILED) { > perror("mmap failed"); > return 1; > } > > memset(addr, 0, SIZE_BYTES); > > struct timespec start, end; > clock_gettime(CLOCK_MONOTONIC, &start); > > if (madvise(addr, SIZE_BYTES, MADV_PAGEOUT) != 0) { > perror("madvise(MADV_PAGEOUT) failed"); > munmap(addr, SIZE_BYTES); > return 1; > } > > clock_gettime(CLOCK_MONOTONIC, &end); > > long duration_ns = (end.tv_sec - start.tv_sec) * 1e9 + > (end.tv_nsec - start.tv_nsec); > printf("madvise(MADV_PAGEOUT) took %ld ns (%.3f ms)\n", > duration_ns, duration_ns / 1e6); > > munmap(addr, SIZE_BYTES); > return 0; > } > > Performance as measured on a Linux VM on Apple M3 (arm64): > > Vanilla - Mean: 37401913 ns, std dev: 12% > Patched - Mean: 17420282 ns, std dev: 11% > > resulting in more than 2x speedup. > > No regression observed on 4K folios. > > Performance as measured on bare metal x86: > > Vanilla - mean: 54986286 ns, std dev: 1.5% > Patched - mean: 51930795 ns, std dev: 3% > > I tried magnifying the difference on x86 by using 1M large folios, but > can't spot an obvious improvement (looks like my system is too fast to > benefit from batched atomic operations!), hinting that the benefit lies > mainly in the reduction of ptep_get() calls and the reduction of TLB > flushes during contpte-unfolding, on arm64. > > No regression is observed on 4K folios on x86 too. > > --- > Applies on mm-unstable. Given that we are approaching rc6 and are flooded with stuff, this will target 7.5. I have this on my todo list. -- Cheers, David