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 EF955136352 for ; Thu, 9 Jan 2025 06:27:47 +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=1736404070; cv=none; b=MpvYnRRFJtA2xb/GPdVsSDHT1AYiK83JXNQdGLQoowzmGtVz8fVQleqK9GQClWtFhde513yiy+kCtOUoSzmc14K+3ZY+U79rdt9WFuXShsqyXXSenDsefTcaBnrcEvHmqjfqByf65akNBxWYsHlaTaiakfNFgVJI+QRB2JOf79s= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1736404070; c=relaxed/simple; bh=bWBNq86L8bmzu2vi0S8FGNv4HquWwWA+7SeUbkEQHK4=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=tnnMH0aEn+lhYSL3LVHJ62OGSYU3s6H0DiTGJOUEVWKEaC4vIZqwVbfkxcvdUvT+iCaiFMutMGx83btCqgB/N0IeKjFL35/RNAsxHschXLXF3uXWqnkjZBsnBDZlA3c9jfPHWdOX07s83OyYq7gm8tRG3i6p7JF6nRF2AGIKkC4= 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 3AC291516; Wed, 8 Jan 2025 22:28:15 -0800 (PST) Received: from [10.162.43.52] (K4MQJ0H1H2.blr.arm.com [10.162.43.52]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 806903F59E; Wed, 8 Jan 2025 22:27:35 -0800 (PST) Message-ID: Date: Thu, 9 Jan 2025 11:57:32 +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 , linux-kernel@vger.kernel.org, linux-mm@kvack.org Cc: 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> Content-Language: en-US From: Dev Jain In-Reply-To: <20250108233128.14484-1-npache@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit 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(-) >