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imf08.hostedemail.com; dkim=none; spf=pass (imf08.hostedemail.com: domain of dev.jain@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=dev.jain@arm.com; dmarc=pass (policy=none) header.from=arm.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1739278200; a=rsa-sha256; cv=none; b=jwiqPqw1tMHh6uZggxB6zGNuwu3zMbs1V3T8BL3JDXKBoNpbtrjdflbn6ZxeS0CM64+Ijx tafBGDBZBDOr2PwvymOhG8BFX4wpgEkZPFfV/gAx+A8f2C93HhwM8zJcyps3qRFyjszGuO c5LduG2qG+9ZHLaaPFwLoRIW95VI4+k= 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 0A29D1424; Tue, 11 Feb 2025 04:50:21 -0800 (PST) Received: from [10.163.92.34] (unknown [10.163.92.34]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id C9D203F5A1; Tue, 11 Feb 2025 04:49:46 -0800 (PST) Message-ID: <5a995dc9-fee7-442f-b439-c484d9de1750@arm.com> Date: Tue, 11 Feb 2025 18:19:43 +0530 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC v2 0/9] khugepaged: mTHP support To: Nico Pache , linux-kernel@vger.kernel.org, linux-trace-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, rostedt@goodmis.org, mathieu.desnoyers@efficios.com, tiwai@suse.de References: <20250211003028.213461-1-npache@redhat.com> Content-Language: en-US From: Dev Jain In-Reply-To: <20250211003028.213461-1-npache@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Queue-Id: 76D65160003 X-Stat-Signature: m5kpbnyubi3zhiyucsfd3wfiroc38edm X-Rspamd-Server: rspam03 X-HE-Tag: 1739278200-137202 X-HE-Meta: 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 9+h0u+S5 Hvi8BKvIGdWdhRVuZnQoTwkly8gsWecF15sbNALUVmsZkbYIwlNFeFi1+FHB9+u5LrRC8wXyn35fU22wX3qy8UFQ6iPRv+0MhbGpkC7x1549EE2XOwDjdvALC91Zn4qYrctldZ32ZXFGghYIICc4I5+p+gdk+CoBQAhkaPe3jzuHFYe19EAzFIP4ywjs1eJ4rzxNckhLm/ZvksGsN9RLsl8uhIqV/gUSdWsR0PrxBXN2qK6Q99iylzCI0feQ3lQ4UyhxNbOqMPlQJjqKkbQWhFkyLvPMt2FZd7qLIN6a7FdR9LxodjWe8nDRr4mgUj23HPidMnZDmmp7SGQN8rfDu7FC8BA== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 11/02/25 6:00 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 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 will be scaled by the attempted collapse > order to determine how full a THP must be to be eligible. If a mTHP collapse > is attempted, but contains swapped out, or shared pages, we dont perform the > collapse. > > With the default max_ptes_none=511, the code should keep its most of its > original behavior. To exercise mTHP collapse we need to set max_ptes_none<=255. > With max_ptes_none > HPAGE_PMD_NR/2 you will experience collapse "creep" and > constantly promote mTHPs to the next available size. > > Patch 1: Some refactoring to combine madvise_collapse and khugepaged > Patch 2: Refactor/rename hpage_collapse > Patch 3-5: Generalize khugepaged functions for arbitrary orders > Patch 6-9: The mTHP patches > > --------- > Testing > --------- > - Built for x86_64, aarch64, ppc64le, and s390x > - selftests mm > - I created a test script that I used to push khugepaged to its limits while > monitoring a number of stats and tracepoints. The code is available > here[1] (Run in legacy mode for these changes and set mthp sizes to inherit) > The summary from my testings was that there was no significant regression > noticed through this test. In some cases my changes had better collapse > latencies, and was able to scan more pages in the same amount of time/work, > but for the most part the results were consistant. > - redis testing. I tested these changes along with my defer changes > (see followup post for more details). > - some basic testing on 64k page size. > - lots of general use. These changes have been running in my VM for some time. > > Changes since V1 [2]: > - Minor bug fixes discovered during review and testing > - removed dynamic allocations for bitmaps, and made them stack based > - Adjusted bitmap offset from u8 to u16 to support 64k pagesize. > - Updated trace events to include collapsing order info. > - Scaled max_ptes_none by order rather than scaling to a 0-100 scale. > - No longer require a chunk to be fully utilized before setting the bit. Use > the same max_ptes_none scaling principle to achieve this. > - Skip mTHP collapse that requires swapin or shared handling. This helps prevent > some of the "creep" that was discovered in v1. > > [1] - https://gitlab.com/npache/khugepaged_mthp_test > [2] - https://lore.kernel.org/lkml/20250108233128.14484-1-npache@redhat.com/ > > Nico Pache (9): > introduce khugepaged_collapse_single_pmd to unify khugepaged and > madvise_collapse > 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: improve tracepoints for mTHP orders > khugepaged: skip collapsing mTHP to smaller orders > > include/linux/khugepaged.h | 4 + > include/trace/events/huge_memory.h | 34 ++- > mm/khugepaged.c | 422 +++++++++++++++++++---------- > 3 files changed, 306 insertions(+), 154 deletions(-) > Does this patchset suffer from the problem described here: https://lore.kernel.org/all/8abd99d5-329f-4f8d-8680-c2d48d4963b6@arm.com/