From nobody Sun Feb 8 04:11:09 2026 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 1F1CCC4167D for ; Mon, 30 Oct 2023 01:13:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231224AbjJ3BMH (ORCPT ); Sun, 29 Oct 2023 21:12:07 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47790 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229470AbjJ3BMF (ORCPT ); Sun, 29 Oct 2023 21:12:05 -0400 Received: from out30-124.freemail.mail.aliyun.com (out30-124.freemail.mail.aliyun.com [115.124.30.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B587DBD for ; Sun, 29 Oct 2023 18:12:01 -0700 (PDT) X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R381e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=ay29a033018045192;MF=baolin.wang@linux.alibaba.com;NM=1;PH=DS;RN=6;SR=0;TI=SMTPD_---0Vv4ZEFb_1698628318; Received: from localhost(mailfrom:baolin.wang@linux.alibaba.com fp:SMTPD_---0Vv4ZEFb_1698628318) by smtp.aliyun-inc.com; Mon, 30 Oct 2023 09:11:59 +0800 From: Baolin Wang To: akpm@linux-foundation.org Cc: shy828301@gmail.com, ying.huang@intel.com, baolin.wang@linux.alibaba.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: [PATCH] mm: huge_memory: batch tlb flush when splitting a pte-mapped THP Date: Mon, 30 Oct 2023 09:11:47 +0800 Message-Id: <431d9fb6823036369dcb1d3b2f63732f01df21a7.1698488264.git.baolin.wang@linux.alibaba.com> X-Mailer: git-send-email 2.39.3 MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" I can observe an obvious tlb flush hotpot when splitting a pte-mapped THP on my ARM64 server, and the distribution of this hotspot is as follows: - 16.85% split_huge_page_to_list + 7.80% down_write - 7.49% try_to_migrate - 7.48% rmap_walk_anon 7.23% ptep_clear_flush + 1.52% __split_huge_page The reason is that the split_huge_page_to_list() will build migration entri= es for each subpage of a pte-mapped Anon THP by try_to_migrate(), or unmap for file THP, and it will clear and tlb flush for each subpage's pte. Moreover, the split_huge_page_to_list() will set TTU_SPLIT_HUGE_PMD flag to ensure the THP is already a pte-mapped THP before splitting it to some normal page= s. Actually, there is no need to flush tlb for each subpage immediately, inste= ad we can batch tlb flush for the pte-mapped THP to improve the performance. After this patch, we can see the batch tlb flush can improve the latency obviously when running thpscale. k6.5-base patched Amean fault-both-1 1071.17 ( 0.00%) 901.83 * 15.81%* Amean fault-both-3 2386.08 ( 0.00%) 1865.32 * 21.82%* Amean fault-both-5 2851.10 ( 0.00%) 2273.84 * 20.25%* Amean fault-both-7 3679.91 ( 0.00%) 2881.66 * 21.69%* Amean fault-both-12 5916.66 ( 0.00%) 4369.55 * 26.15%* Amean fault-both-18 7981.36 ( 0.00%) 6303.57 * 21.02%* Amean fault-both-24 10950.79 ( 0.00%) 8752.56 * 20.07%* Amean fault-both-30 14077.35 ( 0.00%) 10170.01 * 27.76%* Amean fault-both-32 13061.57 ( 0.00%) 11630.08 * 10.96%* Signed-off-by: Baolin Wang Reviewed-by: "Huang, Ying" Reviewed-by: Yang Shi --- mm/huge_memory.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/mm/huge_memory.c b/mm/huge_memory.c index f31f02472396..0e4c14bf6872 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -2379,7 +2379,7 @@ void vma_adjust_trans_huge(struct vm_area_struct *vma, static void unmap_folio(struct folio *folio) { enum ttu_flags ttu_flags =3D TTU_RMAP_LOCKED | TTU_SPLIT_HUGE_PMD | - TTU_SYNC; + TTU_SYNC | TTU_BATCH_FLUSH; =20 VM_BUG_ON_FOLIO(!folio_test_large(folio), folio); =20 @@ -2392,6 +2392,8 @@ static void unmap_folio(struct folio *folio) try_to_migrate(folio, ttu_flags); else try_to_unmap(folio, ttu_flags | TTU_IGNORE_MLOCK); + + try_to_unmap_flush(); } =20 static void remap_page(struct folio *folio, unsigned long nr) --=20 2.39.3