Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752346AbdCOI76 (ORCPT ); Wed, 15 Mar 2017 04:59:58 -0400 Received: from mga05.intel.com ([192.55.52.43]:30134 "EHLO mga05.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751195AbdCOI74 (ORCPT ); Wed, 15 Mar 2017 04:59:56 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.36,168,1486454400"; d="scan'208";a="67566341" From: Aaron Lu To: linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: Dave Hansen , Tim Chen , Andrew Morton , Ying Huang , Aaron Lu Subject: [PATCH v2 0/5] mm: support parallel free of memory Date: Wed, 15 Mar 2017 16:59:59 +0800 Message-Id: <1489568404-7817-1-git-send-email-aaron.lu@intel.com> X-Mailer: git-send-email 2.7.4 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4165 Lines: 99 For regular processes, the time taken in its exit() path to free its used memory is not a problem. But there are heavy ones that consume several Terabytes memory and the time taken to free its memory in its exit() path could last more than ten minutes if THP is not used. As Dave Hansen explained why do this in kernel: " One of the places we saw this happen was when an app crashed and was exit()'ing under duress without cleaning up nicely. The time that it takes to unmap a few TB of 4k pages is pretty excessive. " To optimize this use case, a parallel free method is proposed here and it is based on the current gather batch free(the following description is taken from patch 2/5's changelog). The current gather batch free works like this: For each struct mmu_gather *tlb, there is a static buffer to store those to-be-freed page pointers. The size is MMU_GATHER_BUNDLE, which is defined to be 8. So if a tlb tear down doesn't free more than 8 pages, that is all we need. If 8+ pages are to be freed, new pages will need to be allocated to store those to-be-freed page pointers. The structure used to describe the saved page pointers is called struct mmu_gather_batch and tlb->local is of this type. tlb->local is different than other struct mmu_gather_batch(es) in that the page pointer array used by tlb->local points to the previouslly described static buffer while the other struct mmu_gather_batch(es) page pointer array points to the dynamically allocated pages. These batches will form a singly linked list, starting from &tlb->local. tlb->local.pages => tlb->pages(8 pointers) \|/ next => batch1->pages => about 510 pointers \|/ next => batch2->pages => about 510 pointers \|/ next => batch3->pages => about 510 pointers ... ... The proposed parallel free did this: if the process has many pages to be freed, accumulate them in these struct mmu_gather_batch(es) one after another till 256K pages are accumulated. Then take this singly linked list starting from tlb->local.next off struct mmu_gather *tlb and free them in a worker thread. The main thread can return to continue zap other pages(after freeing pages pointed by tlb->local.pages). A test program that did a single malloc() of 320G memory is used to see how useful the proposed parallel free solution is, the time calculated is for the free() call. Test machine is a Haswell EX which has 4nodes/72cores/144threads with 512G memory. All tests are done with THP disabled. kernel time v4.10 10.8s ±2.8% this patch(with default setting) 5.795s ±5.8% Patch 3/5 introduced a dedicated workqueue for the free workers and here are more results when setting different values for max_active of this workqueue: max_active: time 1 8.9s ±0.5% 2 5.65s ±5.5% 4 4.84s ±0.16% 8 4.77s ±0.97% 16 4.85s ±0.77% 32 6.21s ±0.46% Comments are welcome and appreciated. v2 changes: Nothing major, only minor ones. - rebased on top of v4.11-rc2-mmotm-2017-03-14-15-41; - use list_add_tail instead of list_add to add worker to tlb's worker list so that when doing flush, the first queued worker gets flushed first(based on the comsumption that the first queued worker has a better chance of finishing its job than those later queued workers); - use bool instead of int for variable free_batch_page in function tlb_flush_mmu_free_batches; - style change according to ./scripts/checkpatch; - reword some of the changelogs to make it more readable. v1 is here: https://lkml.org/lkml/2017/2/24/245 Aaron Lu (5): mm: add tlb_flush_mmu_free_batches mm: parallel free pages mm: use a dedicated workqueue for the free workers mm: add force_free_pages in zap_pte_range mm: add debugfs interface for parallel free tuning include/asm-generic/tlb.h | 15 ++--- mm/memory.c | 141 +++++++++++++++++++++++++++++++++++++++------- 2 files changed, 128 insertions(+), 28 deletions(-) -- 2.7.4