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 A6D8B79D0 for ; Fri, 10 Jan 2025 04:56:33 +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=1736484997; cv=none; b=RZ7AKabjBAdjEfEfz+xMHRks+0I6ZPc9qxLLQDRUdgfgKMp49TFkrXcE07oA0HOjucu3/7juwLEs9ck5WAiiP0eVYCA5sXAqzG6UHbvy35fpgEAK0tOyjknDb+9jw0dTKZPCV9BK/fl1FqcNUb+fzRg9M7LROk+5ZS3NBqI7Wrk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1736484997; c=relaxed/simple; bh=MnRADw75Ybd9eBTefawlPQ9u8Zu0qAPKPBA92uXrzUo=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=Vk7fm3gc++rDxKUCoP1wy3aM/PWeTq4cEXC61n2WRxvQu5xwsvJZyTFIWOVYGqzgVMwyw6eRGi5bz6yZyI8GKQJw6HO+vq8CSm6dIyv9z5QjjkE3ijEurO7tkb1CKQxihCoJthi6SsP72C88TtDax5zW4f733PXDrL+pSmanXlo= 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 E06AA1477; Thu, 9 Jan 2025 20:57:00 -0800 (PST) Received: from [10.162.42.21] (K4MQJ0H1H2.blr.arm.com [10.162.42.21]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id A4D883F673; Thu, 9 Jan 2025 20:56:20 -0800 (PST) Message-ID: <4ab296ec-5dd2-4d1f-a823-29396cade93e@arm.com> Date: Fri, 10 Jan 2025 10:26:17 +0530 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: [RFC 00/11] khugepaged: mTHP support To: Nico Pache Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, ryan.roberts@arm.com, anshuman.khandual@arm.com, catalin.marinas@arm.com, cl@gentwo.org, vbabka@suse.cz, mhocko@suse.com, apopple@nvidia.com, dave.hansen@linux.intel.com, will@kernel.org, baohua@kernel.org, jack@suse.cz, srivatsa@csail.mit.edu, haowenchao22@gmail.com, hughd@google.com, aneesh.kumar@kernel.org, yang@os.amperecomputing.com, peterx@redhat.com, ioworker0@gmail.com, wangkefeng.wang@huawei.com, ziy@nvidia.com, jglisse@google.com, surenb@google.com, vishal.moola@gmail.com, zokeefe@google.com, zhengqi.arch@bytedance.com, jhubbard@nvidia.com, 21cnbao@gmail.com, willy@infradead.org, kirill.shutemov@linux.intel.com, david@redhat.com, aarcange@redhat.com, raquini@redhat.com, sunnanyong@huawei.com, usamaarif642@gmail.com, audra@redhat.com, akpm@linux-foundation.org References: <20250108233128.14484-1-npache@redhat.com> <3e3252c2-65fc-45aa-99a1-ed66c31aba12@arm.com> Content-Language: en-US From: Dev Jain In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 10/01/25 7:57 am, Nico Pache wrote: > On Wed, Jan 8, 2025 at 11:22 PM Dev Jain wrote: >> >> >> On 09/01/25 5:01 am, Nico Pache wrote: >>> The following series provides khugepaged and madvise collapse with the >>> capability to collapse regions to mTHPs. >>> >>> To achieve this we generalize the khugepaged functions to no longer depend >>> on PMD_ORDER. Then during the PMD scan, we keep track of chunks of pages >>> (defined by MTHP_MIN_ORDER) that are fully utilized. This info is tracked >>> using a bitmap. After the PMD scan is done, we do binary recursion on the >>> bitmap to find the optimal mTHP sizes for the PMD range. The restriction >>> on max_ptes_none is removed during the scan, to make sure we account for >>> the whole PMD range. max_ptes_none is mapped to a 0-100 range to >>> determine how full a mTHP order needs to be before collapsing it. >>> >>> Some design choices to note: >>> - bitmap structures are allocated dynamically because on some arch's >>> (like PowerPC) the value of MTHP_BITMAP_SIZE cannot be computed at >>> compile time leading to warnings. >>> - The recursion is masked through a stack structure. >>> - A MTHP_MIN_ORDER was added to compress the bitmap, and ensure it was >>> 64bit on x86. This provides some optimization on the bitmap operations. >>> if other arches/configs that have larger than 512 PTEs per PMD want to >>> compress their bitmap further we can change this value per arch. >>> >>> Patch 1-2: Some refactoring to combine madvise_collapse and khugepaged >>> Patch 3: A minor "fix"/optimization >>> Patch 4: Refactor/rename hpage_collapse >>> Patch 5-7: Generalize khugepaged functions for arbitrary orders >>> Patch 8-11: The mTHP patches >>> >>> This series acts as an alternative to Dev Jain's approach [1]. The two >>> series differ in a few ways: >>> - My approach uses a bitmap to store the state of the linear scan_pmd to >>> then determine potential mTHP batches. Devs incorporates his directly >>> into the scan, and will try each available order. >>> - Dev is attempting to optimize the locking, while my approach keeps the >>> locking changes to a minimum. I believe his changes are not safe for >>> uffd. >>> - Dev's changes only work for khugepaged not madvise_collapse (although >>> i think that was by choice and it could easily support madvise) >>> - Dev scales all khugepaged sysfs tunables by order, while im removing >>> the restriction of max_ptes_none and converting it to a scale to >>> determine a (m)THP threshold. >>> - Dev turns on khugepaged if any order is available while mine still >>> only runs if PMDs are enabled. I like Dev's approach and will most >>> likely do the same in my PATCH posting. >>> - mTHPs need their ref count updated to 1<>> >>> Patch 11 was inspired by one of Dev's changes. >>> >>> [1] https://lore.kernel.org/lkml/20241216165105.56185-1-dev.jain@arm.com/ >>> >>> Nico Pache (11): >>> introduce khugepaged_collapse_single_pmd to collapse a single pmd >>> khugepaged: refactor madvise_collapse and khugepaged_scan_mm_slot >>> khugepaged: Don't allocate khugepaged mm_slot early >>> khugepaged: rename hpage_collapse_* to khugepaged_* >>> khugepaged: generalize hugepage_vma_revalidate for mTHP support >>> khugepaged: generalize alloc_charge_folio for mTHP support >>> khugepaged: generalize __collapse_huge_page_* for mTHP support >>> khugepaged: introduce khugepaged_scan_bitmap for mTHP support >>> khugepaged: add mTHP support >>> khugepaged: remove max_ptes_none restriction on the pmd scan >>> khugepaged: skip collapsing mTHP to smaller orders >>> >>> include/linux/khugepaged.h | 4 +- >>> mm/huge_memory.c | 3 +- >>> mm/khugepaged.c | 436 +++++++++++++++++++++++++------------ >>> 3 files changed, 306 insertions(+), 137 deletions(-) >> >> Before I take a proper look at your series, can you please include any testing >> you may have done? > > I Built these changes for the following arches: x86_64, arm64, > arm64-64k, ppc64le, s390x > > x86 testing: > - Selftests mm > - some stress-ng tests > - compile kernel > - I did some tests with my defer [1] set on top. This pushes all the > work to khugepaged, which removes the noise of all the PF allocations. > > I recently got an ARM64 machine and did some simple sanity tests (on > both 4k and 64k) like selftests, stress-ng, and playing around with > the tunables, etc. > > I will also be running all the builds through our CI, and perf testing > environments before posting. > > [1] https://lore.kernel.org/lkml/20240729222727.64319-1-npache@redhat.com/ > >> > I tested your series with the program I was using and it is not working; can you please confirm it. diff --git a/mytests/mthp.c b/mytests/mthp.c new file mode 100644 index 000000000000..e3029dbcf035 --- /dev/null +++ b/mytests/mthp.c @@ -0,0 +1,45 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * + * Author: Dev Jain + * + * Program to test khugepaged mTHP collapse + */ + +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include + +int main(int argc, char *argv[]) +{ + char *ptr; + unsigned long mthp_size = (1UL << 16); + size_t chunk_size = (1UL << 25); + + ptr = mmap((void *)(1UL << 30), chunk_size, PROT_READ | PROT_WRITE, + MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); + if (((unsigned long)ptr) != (1UL << 30)) { + printf("mmap did not work on required address\n"); + return 1; + } + + /* Fill first pte in every 64K interval */ + for (int i = 0; i < chunk_size; i += mthp_size) + ptr[i] = i; + + if (madvise(ptr, chunk_size, MADV_HUGEPAGE)) { + perror("madvise"); + return 1; + } + sleep(100); + return 0; +} -- 2.30.2 Set enabled = madvise, hugepages-2048k/enabled = hugepages-64k/enabled = inherit. Run the program in the background, then run tools/mm/thpmaps. You will see PMD collapse correctly, but when you echo never into hugepages-2048k/enabled and test this again, you won't see contpte 64K collapse. With my series, you will see something like anon-cont-pte-aligned-64kB : 32768 kB (100%).