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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id CC899CA0EC3 for ; Tue, 12 Sep 2023 13:43:33 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235650AbjILNng (ORCPT ); Tue, 12 Sep 2023 09:43:36 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52614 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235637AbjILNnd (ORCPT ); Tue, 12 Sep 2023 09:43:33 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 4561910D0 for ; Tue, 12 Sep 2023 06:42:43 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1694526162; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=+YST80+96+FKeOUG6Mux+YnG1fWt/FfWscMZ4ez6DB4=; b=jFJEvn0VJfbw7Xald01mFS6g/14syTwhfnEpHg0DDXZR0CWgnAbYURXoCIKYPtOS3yp/q7 mdiQlT0nG5a6+6DMM0ZkBSp60STMmpUDmiyfbbocwS3M3f3BNdWcVHqh/EcfFat05U8Ztb lE79R4kEXk4IQsk4RJ+C4QZfB5WIapA= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-538-fobPUqw1PdKY6DSFUOmluA-1; Tue, 12 Sep 2023 09:42:38 -0400 X-MC-Unique: fobPUqw1PdKY6DSFUOmluA-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.rdu2.redhat.com [10.11.54.3]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id C2E8C101FAA3; Tue, 12 Sep 2023 13:42:37 +0000 (UTC) Received: from localhost (unknown [10.72.112.25]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 08A5410085C0; Tue, 12 Sep 2023 13:42:35 +0000 (UTC) Date: Tue, 12 Sep 2023 21:42:32 +0800 From: Baoquan He To: Uladzislau Rezki Cc: linux-mm@kvack.org, Andrew Morton , LKML , Lorenzo Stoakes , Christoph Hellwig , Matthew Wilcox , "Liam R . Howlett" , Dave Chinner , "Paul E . McKenney" , Joel Fernandes , Oleksiy Avramchenko Subject: Re: [PATCH v2 7/9] mm: vmalloc: Support multiple nodes in vread_iter Message-ID: References: <20230829081142.3619-1-urezki@gmail.com> <20230829081142.3619-8-urezki@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Scanned-By: MIMEDefang 3.1 on 10.11.54.3 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09/11/23 at 08:16pm, Uladzislau Rezki wrote: > On Mon, Sep 11, 2023 at 11:58:13AM +0800, Baoquan He wrote: > > On 08/29/23 at 10:11am, Uladzislau Rezki (Sony) wrote: > > > Extend the vread_iter() to be able to perform a sequential > > > reading of VAs which are spread among multiple nodes. So a > > > data read over the /dev/kmem correctly reflects a vmalloc > > > memory layout. > > > > > > Signed-off-by: Uladzislau Rezki (Sony) > > > --- > > > mm/vmalloc.c | 67 +++++++++++++++++++++++++++++++++++++++++----------- > > > 1 file changed, 53 insertions(+), 14 deletions(-) > > > > > > diff --git a/mm/vmalloc.c b/mm/vmalloc.c > > > index 4fd4915c532d..968144c16237 100644 > > > --- a/mm/vmalloc.c > > > +++ b/mm/vmalloc.c > > ...... > > > @@ -4057,19 +4093,15 @@ long vread_iter(struct iov_iter *iter, const char *addr, size_t count) > > > > > > remains = count; > > > > > > - /* Hooked to node_0 so far. */ > > > - vn = addr_to_node(0); > > > - spin_lock(&vn->busy.lock); > > > > This could change the vread behaviour a little bit. Before, once we take > > vmap_area_lock, the vread will read out the content of snapshot at the > > moment. Now, reading out in one node's tree won't disrupt other nodes' > > tree accessing. Not sure if this matters when people need access > > /proc/kcore, e.g dynamic debugging. > > > With one big tree you anyway drop the lock after one cycle of reading. > As far as i see, kcore.c's read granularity is a PAGE_SIZE. With my understanding, kcore reading on vmalloc does read page by page, it will continue after one page reading if the required size is bigger than one page. Please see aligned_vread_iter() code. During the complete process, vmap_area_lock is held before this patch. > > > > > And, the reading will be a little slower because each va finding need > > iterate all vmap_nodes[]. > > > Right. It is a bit tough here, because we have multiple nodes which > represent zones(address space), i.e. there is an offset between them, > it means that, reading fully one tree, will not provide a sequential > reading. Understood. Suppose the kcore reading on vmalloc is not critical. If I get chance to test on a machine with 256 cpu, I will report here.