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Wed, 19 Feb 2025 17:00:53 +0000 (UTC) X-FDA: 83137308786.21.3846F65 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by imf20.hostedemail.com (Postfix) with ESMTP id 0C6431C0035 for ; Wed, 19 Feb 2025 17:00:46 +0000 (UTC) Authentication-Results: imf20.hostedemail.com; dkim=none; spf=pass (imf20.hostedemail.com: domain of ryan.roberts@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=ryan.roberts@arm.com; dmarc=pass (policy=none) header.from=arm.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1739984447; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=EN7syeFXzVXvmtruzX5Z+GGT0I+eQQ5zsYlPo0OIYkM=; b=f2OCqSbtcDDDtEd0v96A8voEysGBiytkYKUcqQDcBZsEfqsyoXlxmxTpN8ZYaRezhc7DHl Z22Yl767CO8pbevD3Psiz9xkMwuD2MTaL6NS71M3lu3R/JHYz2KKRdtOzIH5VhtVQRD7af PGOr+whmYZoO66LVpji/tGs02cGzhE0= ARC-Authentication-Results: i=1; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 0C6431C0035 X-Stat-Signature: icrk9tie7giic85a8i9of4yy9ngjj6pu X-Rspam-User: X-Rspamd-Server: rspam01 X-HE-Tag: 1739984446-549422 X-HE-Meta: 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 sTWaiAYs mTrPA+96GLhyotDEUEG6IzwZlqaOdJOasooE/NYLtWfKyrUAz1m1svfn/kW6zeh6panq5KciN7MIXXABE1uW1mbTCKUohU2/YSnhE1wW7Pwj0LCRJ8pqqJ8Xf5/8YUplDQsQnArgXgnO1NZrQEjlo53KaN2r8A1/E9tO4ssz+i/kp+8JbD15erjQ1ELh4m3YDTTmm8eOgqO0d8PdC1BZR4JhMdx6Emr3rtnXOcP8JC3R+KvI9N3WDoalRieim37Y8RRCCME7zjktTQPdW559l+e8oFiF8aMX2wofB 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 11/02/2025 00:30, 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. Having been through the code I don't think you can handle the case of a partially covered PMD? That was never important before because by definition we only cared about PMD-sized chunks, but it would be good to be able to collapse to appropriately sized mTHP, memory within a VMA that doesn't cover an entire PMD. Do you have plans to add that? Is the approach you've taken amenable to extension in this way? > 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(-) >