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 lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 384DEC54E60 for ; Tue, 19 Mar 2024 13:44:11 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1rmZkp-0000LC-Uo; Tue, 19 Mar 2024 09:43:47 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1rmZko-0000Kp-FE for qemu-devel@nongnu.org; Tue, 19 Mar 2024 09:43:46 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1rmZkm-0003Xd-Dd for qemu-devel@nongnu.org; Tue, 19 Mar 2024 09:43:46 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1710855822; h=from:from:reply-to: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=txDTDRa29mOwqVwt1WygCy1tWyRzi+Udm6UuwF7lexU=; b=HBJU7G1+7kefHIywemUNSWeKUvcBHZeU/YO5hiHbltH5iI40YteCEgUEY7dEsrry3/WSXE rBGhyKdFd4fT4m0bOofkE7WTNkGNgdm3iIltjHVabFWJBSjMpqVIQFhE+djFUC9NV5c0sg iVhx+4PB8SqlPwH4IHw/sdLTrhPv1E0= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-690-w7JwCYhtMluEvvO6cwN2eA-1; Tue, 19 Mar 2024 09:43:40 -0400 X-MC-Unique: w7JwCYhtMluEvvO6cwN2eA-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.rdu2.redhat.com [10.11.54.7]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id C3683800268 for ; Tue, 19 Mar 2024 13:43:39 +0000 (UTC) Received: from redhat.com (unknown [10.42.28.88]) by smtp.corp.redhat.com (Postfix) with ESMTPS id EB6C41C060A4; Tue, 19 Mar 2024 13:43:38 +0000 (UTC) Date: Tue, 19 Mar 2024 13:43:32 +0000 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Stefan Hajnoczi Cc: qemu-devel@nongnu.org, Kevin Wolf , Sanjay Rao , Boaz Ben Shabat , Joe Mario Subject: Re: [PATCH] coroutine: cap per-thread local pool size Message-ID: References: <20240318183429.1039340-1-stefanha@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20240318183429.1039340-1-stefanha@redhat.com> User-Agent: Mutt/2.2.12 (2023-09-09) X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.7 Received-SPF: pass client-ip=170.10.133.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -24 X-Spam_score: -2.5 X-Spam_bar: -- X-Spam_report: (-2.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.422, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Mon, Mar 18, 2024 at 02:34:29PM -0400, Stefan Hajnoczi wrote: > The coroutine pool implementation can hit the Linux vm.max_map_count > limit, causing QEMU to abort with "failed to allocate memory for stack" > or "failed to set up stack guard page" during coroutine creation. > > This happens because per-thread pools can grow to tens of thousands of > coroutines. Each coroutine causes 2 virtual memory areas to be created. This sounds quite alarming. What usage scenario is justified in creating so many coroutines ? IIUC, coroutine stack size is 1 MB, and so tens of thousands of coroutines implies 10's of GB of memory just on stacks alone. > Eventually vm.max_map_count is reached and memory-related syscalls fail. On my system max_map_count is 1048576, quite alot higher than 10's of 1000's. Hitting that would imply ~500,000 coroutines and ~500 GB of stacks ! > diff --git a/util/qemu-coroutine.c b/util/qemu-coroutine.c > index 5fd2dbaf8b..2790959eaf 100644 > --- a/util/qemu-coroutine.c > +++ b/util/qemu-coroutine.c > +static unsigned int get_global_pool_hard_max_size(void) > +{ > +#ifdef __linux__ > + g_autofree char *contents = NULL; > + int max_map_count; > + > + /* > + * Linux processes can have up to max_map_count virtual memory areas > + * (VMAs). mmap(2), mprotect(2), etc fail with ENOMEM beyond this limit. We > + * must limit the coroutine pool to a safe size to avoid running out of > + * VMAs. > + */ > + if (g_file_get_contents("/proc/sys/vm/max_map_count", &contents, NULL, > + NULL) && > + qemu_strtoi(contents, NULL, 10, &max_map_count) == 0) { > + /* > + * This is a conservative upper bound that avoids exceeding > + * max_map_count. Leave half for non-coroutine users like library > + * dependencies, vhost-user, etc. Each coroutine takes up 2 VMAs so > + * halve the amount again. > + */ > + return max_map_count / 4; That's 256,000 coroutines, which still sounds incredibly large to me. > + } > +#endif > + > + return UINT_MAX; Why UINT_MAX as a default ? If we can't read procfs, we should assume some much smaller sane default IMHO, that corresponds to what current linux default max_map_count would be. > +} > + > +static void __attribute__((constructor)) qemu_coroutine_init(void) > +{ > + qemu_mutex_init(&global_pool_lock); > + global_pool_hard_max_size = get_global_pool_hard_max_size(); > } > -- > 2.44.0 > > With regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|