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=-0.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS autolearn=no 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 D00BEC3B186 for ; Wed, 12 Feb 2020 22:52:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 992A721569 for ; Wed, 12 Feb 2020 22:52:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1581547971; bh=czm5xq+x3zJ0qiiciKQ7bQR74vUISbw6BSBaEMWk+v8=; h=Date:From:To:Cc:Subject:In-Reply-To:References:List-ID:From; b=s4dLhiB/tWArYtoKp5cQgM383TvaBrC5JRZptcyfzIMBPHTJGLyUHwB5tasLKy0TP Foo0knSw0IvY+AZqb3rifBKHSNctX8hHVFvZ1u3vgxidedhU+57k8wZJHF/RO3+vfo Fbmi0G/DA+HY58wy1j5Mi9M+221hfUBlqx1IHZm8= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729212AbgBLWwv (ORCPT ); Wed, 12 Feb 2020 17:52:51 -0500 Received: from mail.kernel.org ([198.145.29.99]:42018 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728185AbgBLWwu (ORCPT ); Wed, 12 Feb 2020 17:52:50 -0500 Received: from localhost.localdomain (c-73-231-172-41.hsd1.ca.comcast.net [73.231.172.41]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 4FD0F21569; Wed, 12 Feb 2020 22:52:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1581547968; bh=czm5xq+x3zJ0qiiciKQ7bQR74vUISbw6BSBaEMWk+v8=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=zuNm1oa0KqzLmGecolzIK96Aen9gbLKh539V852DcgfooBlUqDHM8Dh1WhGN+RCPc 4EJ8rxzhQiP7/9z5DXF9mrG7La8PdWlR8B7b9wdPi+4o3G3lHbzCHXms0sBjRzMwyE 53NBNngLXNx2L9ebFt9dI1YLuLNOQIInbDyUkTtc= Date: Wed, 12 Feb 2020 14:52:47 -0800 From: Andrew Morton To: Wen Yang Cc: Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , Xunlei Pang , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm/slub: Detach node lock from counting free objects Message-Id: <20200212145247.bf89431272038de53dd9d975@linux-foundation.org> In-Reply-To: <20200201031502.92218-1-wenyang@linux.alibaba.com> References: <20200201031502.92218-1-wenyang@linux.alibaba.com> X-Mailer: Sylpheed 3.5.1 (GTK+ 2.24.31; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, 1 Feb 2020 11:15:02 +0800 Wen Yang wrote: > The lock, protecting the node partial list, is taken when couting the free > objects resident in that list. It introduces locking contention when the > page(s) is moved between CPU and node partial lists in allocation path > on another CPU. So reading "/proc/slabinfo" can possibily block the slab > allocation on another CPU for a while, 200ms in extreme cases. If the > slab object is to carry network packet, targeting the far-end disk array, > it causes block IO jitter issue. > > This fixes the block IO jitter issue by caching the total inuse objects in > the node in advance. The value is retrieved without taking the node partial > list lock on reading "/proc/slabinfo". > > ... > > @@ -1768,7 +1774,9 @@ static void free_slab(struct kmem_cache *s, struct page *page) > > static void discard_slab(struct kmem_cache *s, struct page *page) > { > - dec_slabs_node(s, page_to_nid(page), page->objects); > + int inuse = page->objects; > + > + dec_slabs_node(s, page_to_nid(page), page->objects, inuse); Is this right? dec_slabs_node(..., page->objects, page->objects)? If no, we could simply pass the page* to inc_slabs_node/dec_slabs_node and save a function argument. If yes then why? > free_slab(s, page); > } >