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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C6266C4332F for ; Tue, 28 Sep 2021 22:33:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A75D36139D for ; Tue, 28 Sep 2021 22:33:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S243067AbhI1Weo (ORCPT ); Tue, 28 Sep 2021 18:34:44 -0400 Received: from mail.kernel.org ([198.145.29.99]:51600 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238632AbhI1Wen (ORCPT ); Tue, 28 Sep 2021 18:34:43 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id CEA7161391; Tue, 28 Sep 2021 22:33:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1632868383; bh=nqd+d1rQ4VI/NHuytxGymWHg99OvjAWcXpJLjVTFWSU=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=hfzhic+XohYPgPxc6pIxgwHmHhXfkow1zG9a3p3OnctJ5Y5fGGx1U27Tq9Ci5SKvc ALjZxynfLXWab4ONm2/XTZy5lGFsThL/hu8UcranEmKawB8ViP1ihUQrn/coMdoA+I J7P44Jx3BSrcJsPWyQBK7Gi/2+9QO76ALsrnArEY= Date: Tue, 28 Sep 2021 15:33:02 -0700 From: Andrew Morton To: Chen Wandun Cc: , , , , , Subject: Re: [PATCH] mm/vmalloc: fix numa spreading for large hash tables Message-Id: <20210928153302.f87537b5faac8637c3c5eb53@linux-foundation.org> In-Reply-To: <20210928121040.2547407-1-chenwandun@huawei.com> References: <20210928121040.2547407-1-chenwandun@huawei.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 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 28 Sep 2021 20:10:40 +0800 Chen Wandun wrote: > Eric Dumazet reported a strange numa spreading info in [1], and found > commit 121e6f3258fe ("mm/vmalloc: hugepage vmalloc mappings") introduced > this issue [2]. > > Dig into the difference before and after this patch, page allocation has > some difference: > > before: > alloc_large_system_hash > __vmalloc > __vmalloc_node(..., NUMA_NO_NODE, ...) > __vmalloc_node_range > __vmalloc_area_node > alloc_page /* because NUMA_NO_NODE, so choose alloc_page branch */ > alloc_pages_current > alloc_page_interleave /* can be proved by print policy mode */ > > after: > alloc_large_system_hash > __vmalloc > __vmalloc_node(..., NUMA_NO_NODE, ...) > __vmalloc_node_range > __vmalloc_area_node > alloc_pages_node /* choose nid by nuam_mem_id() */ > __alloc_pages_node(nid, ....) > > So after commit 121e6f3258fe ("mm/vmalloc: hugepage vmalloc mappings"), > it will allocate memory in current node instead of interleaving allocate > memory. > > [1] > https://lore.kernel.org/linux-mm/CANn89iL6AAyWhfxdHO+jaT075iOa3XcYn9k6JJc7JR2XYn6k_Q@mail.gmail.com/ > > [2] > https://lore.kernel.org/linux-mm/CANn89iLofTR=AK-QOZY87RdUZENCZUT4O6a0hvhu3_EwRMerOg@mail.gmail.com/ > > Fixes: 121e6f3258fe ("mm/vmalloc: hugepage vmalloc mappings") > Reported-by: Eric Dumazet > Signed-off-by: Chen Wandun This seems like it could cause significant performance regressions in some situations? If "yes" then wouldn't a cc:stable be appropriate? And some (perhaps handwavy) quantification of the slowdown would help people understand why we're recommending a backport. If "no" then why the heck do we have that feature in there anyway ;)