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 X-Spam-Level: X-Spam-Status: No, score=-15.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 78ED0C2BBCA for ; Tue, 15 Dec 2020 03:13:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4B16D224DE for ; Tue, 15 Dec 2020 03:13:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728051AbgLODNp (ORCPT ); Mon, 14 Dec 2020 22:13:45 -0500 Received: from mail.kernel.org ([198.145.29.99]:41410 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728101AbgLODNZ (ORCPT ); Mon, 14 Dec 2020 22:13:25 -0500 Date: Mon, 14 Dec 2020 19:12:15 -0800 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1608001935; bh=kuFCS14SHNFqv70fqSszNsxLoZwwR5iNZZ7SXGOk7nc=; h=From:To:Subject:In-Reply-To:From; b=Pcy+i7mGmeq5m63NMDKunUjbCi/0/gHsvLzbSJTWo0XvgyJhZlYXOR1HsyyfqJLSw TTHvZ0a1o3xrU71ER+RVASy5wx74A446RWK3sDFClbtNixT0qAqdCUqyyntQU/iswW X2oGEYosqixQsPRH+aaPUbwOm0buCOo3/yRIBB2g= From: Andrew Morton To: akpm@linux-foundation.org, hannes@cmpxchg.org, linux-mm@kvack.org, mgorman@suse.de, mm-commits@vger.kernel.org, torvalds@linux-foundation.org Subject: [patch 152/200] mm: don't wake kswapd prematurely when watermark boosting is disabled Message-ID: <20201215031215.ZzmH0glWr%akpm@linux-foundation.org> In-Reply-To: <20201214190237.a17b70ae14f129e2dca3d204@linux-foundation.org> User-Agent: s-nail v14.8.16 Precedence: bulk Reply-To: linux-kernel@vger.kernel.org List-ID: X-Mailing-List: mm-commits@vger.kernel.org From: Johannes Weiner Subject: mm: don't wake kswapd prematurely when watermark boosting is disabled On 2-node NUMA hosts we see bursts of kswapd reclaim and subsequent pressure spikes and stalls from cache refaults while there is plenty of free memory in the system. Usually, kswapd is woken up when all eligible nodes in an allocation are full. But the code related to watermark boosting can wake kswapd on one full node while the other one is mostly empty. This may be justified to fight fragmentation, but is currently unconditionally done whether watermark boosting is occurring or not. In our case, many of our workloads' throughput scales with available memory, and pure utilization is a more tangible concern than trends around longer-term fragmentation. As a result we generally disable watermark boosting. Wake kswapd only woken when watermark boosting is requested. Link: https://lkml.kernel.org/r/20201020175833.397286-1-hannes@cmpxchg.org Fixes: 1c30844d2dfe ("mm: reclaim small amounts of memory when an external fragmentation event occurs") Signed-off-by: Johannes Weiner Acked-by: Mel Gorman Signed-off-by: Andrew Morton --- mm/page_alloc.c | 13 +++++++------ 1 file changed, 7 insertions(+), 6 deletions(-) --- a/mm/page_alloc.c~mm-dont-wake-kswapd-prematurely-when-watermark-boosting-is-disabled +++ a/mm/page_alloc.c @@ -2482,12 +2482,12 @@ static bool can_steal_fallback(unsigned return false; } -static inline void boost_watermark(struct zone *zone) +static inline bool boost_watermark(struct zone *zone) { unsigned long max_boost; if (!watermark_boost_factor) - return; + return false; /* * Don't bother in zones that are unlikely to produce results. * On small machines, including kdump capture kernels running @@ -2495,7 +2495,7 @@ static inline void boost_watermark(struc * memory situation immediately. */ if ((pageblock_nr_pages * 4) > zone_managed_pages(zone)) - return; + return false; max_boost = mult_frac(zone->_watermark[WMARK_HIGH], watermark_boost_factor, 10000); @@ -2509,12 +2509,14 @@ static inline void boost_watermark(struc * boosted watermark resulting in a hang. */ if (!max_boost) - return; + return false; max_boost = max(pageblock_nr_pages, max_boost); zone->watermark_boost = min(zone->watermark_boost + pageblock_nr_pages, max_boost); + + return true; } /* @@ -2552,8 +2554,7 @@ static void steal_suitable_fallback(stru * likelihood of future fallbacks. Wake kswapd now as the node * may be balanced overall and kswapd will not wake naturally. */ - boost_watermark(zone); - if (alloc_flags & ALLOC_KSWAPD) + if (boost_watermark(zone) && (alloc_flags & ALLOC_KSWAPD)) set_bit(ZONE_BOOSTED_WATERMARK, &zone->flags); /* We are not allowed to try stealing from the whole block */ _