From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 471DCC25B47 for ; Wed, 25 Oct 2023 14:46:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1343498AbjJYOqC (ORCPT ); Wed, 25 Oct 2023 10:46:02 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:32796 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234655AbjJYOp7 (ORCPT ); Wed, 25 Oct 2023 10:45:59 -0400 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 881CADC for ; Wed, 25 Oct 2023 07:45:56 -0700 (PDT) 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 A7C432F4; Wed, 25 Oct 2023 07:46:37 -0700 (PDT) Received: from e125769.cambridge.arm.com (e125769.cambridge.arm.com [10.1.196.26]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 896F53F64C; Wed, 25 Oct 2023 07:45:54 -0700 (PDT) From: Ryan Roberts To: Andrew Morton , David Hildenbrand , Matthew Wilcox , Huang Ying , Gao Xiang , Yu Zhao , Yang Shi , Michal Hocko , Kefeng Wang Cc: Ryan Roberts , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH v3 0/4] Swap-out small-sized THP without splitting Date: Wed, 25 Oct 2023 15:45:42 +0100 Message-Id: <20231025144546.577640-1-ryan.roberts@arm.com> X-Mailer: git-send-email 2.25.1 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi All, This is v3 of a series to add support for swapping out small-sized THP without needing to first split the large folio via __split_huge_page(). It closely follows the approach already used by PMD-sized THP. "Small-sized THP" is an upcoming feature that enables performance improvements by allocating large folios for anonymous memory, where the large folio size is smaller than the traditional PMD-size. See [3]. In some circumstances I've observed a performance regression (see patch 2 for details), and this series is an attempt to fix the regression in advance of merging small-sized THP support. I've done what I thought was the smallest change possible, and as a result, this approach is only employed when the swap is backed by a non-rotating block device (just as PMD-sized THP is supported today). Discussion against the RFC concluded that this is probably sufficient. The series applies against mm-unstable (1a3c85fa684a) Changes since v2 [2] ==================== - Reuse scan_swap_map_try_ssd_cluster() between order-0 and order > 0 allocation. This required some refactoring to make everything work nicely (new patches 2 and 3). - Fix bug where nr_swap_pages would say there are pages available but the scanner would not be able to allocate them because they were reserved for the per-cpu allocator. We now allow stealing of order-0 entries from the high order per-cpu clusters (in addition to exisiting stealing from order-0 per-cpu clusters). Thanks to Huang, Ying for the review feedback and suggestions! Changes since v1 [1] ==================== - patch 1: - Use cluster_set_count() instead of cluster_set_count_flag() in swap_alloc_cluster() since we no longer have any flag to set. I was unable to kill cluster_set_count_flag() as proposed against v1 as other call sites depend explicitly setting flags to 0. - patch 2: - Moved large_next[] array into percpu_cluster to make it per-cpu (recommended by Huang, Ying). - large_next[] array is dynamically allocated because PMD_ORDER is not compile-time constant for powerpc (fixes build error). Thanks, Ryan P.S. I know we agreed this is not a prerequisite for merging small-sized THP, but given Huang Ying had provided some review feedback, I wanted to progress it. All the actual prerequisites are either complete or being worked on by others. [1] https://lore.kernel.org/linux-mm/20231010142111.3997780-1-ryan.roberts@arm.com/ [2] https://lore.kernel.org/linux-mm/20231017161302.2518826-1-ryan.roberts@arm.com/ [3] https://lore.kernel.org/linux-mm/15a52c3d-9584-449b-8228-1335e0753b04@arm.com/ Ryan Roberts (4): mm: swap: Remove CLUSTER_FLAG_HUGE from swap_cluster_info:flags mm: swap: Remove struct percpu_cluster mm: swap: Simplify ssd behavior when scanner steals entry mm: swap: Swap-out small-sized THP without splitting include/linux/swap.h | 31 +++--- mm/huge_memory.c | 3 - mm/swapfile.c | 232 ++++++++++++++++++++++++------------------- mm/vmscan.c | 10 +- 4 files changed, 149 insertions(+), 127 deletions(-) -- 2.25.1