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 lists1p.gnu.org (lists1p.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 88250CC6B1A for ; Wed, 14 Oct 2026 07:51:39 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists1p.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1xGtlC-0005cH-Mi; Wed, 14 Oct 2026 03:50:50 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists1p.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1xGtlA-0005bm-Fw for qemu-devel@nongnu.org; Wed, 14 Oct 2026 03:50:48 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1xGtl8-00070m-LZ for qemu-devel@nongnu.org; Wed, 14 Oct 2026 03:50:48 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1791964245; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=lE8Rd/c04006GqQtZVHh7dDl52rVATSHQwAtJf/ReNQ=; b=Yz87bINiWnMAY/1nWa7sFCKK66H25fhDFybVmVNTTGTNLuSRHuplW6V3vu+tYDWoqx2MwN bDURaxrFOHGPRKS/xpvhFbD0dD4UGnelSnoRUjyFRedfFEobcK9fUTdgEnsoLXiVt0pTJb 9xCOxX8707+SOyqFRknrz9ybDlk15OY= Received: from mx-prod-mc-06.mail-002.prod.us-west-2.aws.redhat.com (ec2-35-165-154-97.us-west-2.compute.amazonaws.com [35.165.154.97]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-637-g0ghRFhTP1CI--tM5w_5UA-1; Wed, 14 Oct 2026 07:50:41 +0000 X-MC-Unique: g0ghRFhTP1CI--tM5w_5UA-1 X-Mimecast-MFC-AGG-ID: g0ghRFhTP1CI--tM5w_5UA_1791964241 Received: from mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.93]) (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 mx-prod-mc-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 623BA180048E; Wed, 14 Oct 2026 07:50:40 +0000 (UTC) Received: from redhat.com (headnet04.pony-001.prod.iad2.dc.redhat.com [10.2.32.116]) by mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 3890A1800444; Wed, 14 Oct 2026 07:50:36 +0000 (UTC) Date: Wed, 14 Oct 2026 08:50:34 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Wesley Hershberger Cc: qemu-devel@nongnu.org, Stefan Hajnoczi , Kevin Wolf , Hector Cao , alex.ramirez@canonical.com Subject: Re: [PATCH v3 2/2] util/coroutine: Reduce default idle pool max size Message-ID: References: <20261013-set-default-pool-size-v3-0-d36e8c31f9a6@canonical.com> <20261013-set-default-pool-size-v3-2-d36e8c31f9a6@canonical.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20261013-set-default-pool-size-v3-2-d36e8c31f9a6@canonical.com> User-Agent: Mutt/2.4.2 (2026-08-30) X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.93 Received-SPF: pass client-ip=170.10.129.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -22 X-Spam_score: -2.3 X-Spam_bar: -- X-Spam_report: (-2.3 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.24, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 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: qemu development 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 Tue, Oct 13, 2026 at 05:01:01PM -0500, Wesley Hershberger wrote: > If g_file_get_contents fails (AppArmor, etc), use a more conservative > default max size for the idle coroutine pool. > > This avoids any possibility of the failure described in 86a637e48104 > unless the host kernel is configured with a lower-than-default > vm.max_map_count. > > This change is motivated by a discussion of backport risk: > https://bugs.launchpad.net/ubuntu/+source/qemu/+bug/2168803/comments/8 > > Fixes: 86a637e48104 ("coroutine: cap per-thread local pool size") > Suggested-by: Daniel P. Berrangé > Signed-off-by: Wesley Hershberger > --- > util/qemu-coroutine.c | 75 ++++++++++++++++++++++++++++++++------------------- > 1 file changed, 48 insertions(+), 27 deletions(-) > > diff --git a/util/qemu-coroutine.c b/util/qemu-coroutine.c > index 5af61995437..8ced93144fa 100644 > --- a/util/qemu-coroutine.c > +++ b/util/qemu-coroutine.c > @@ -361,42 +361,63 @@ void qemu_coroutine_dec_pool_size(unsigned int removing_pool_size) > global_pool_max_size -= removing_pool_size; > } > > -static unsigned int get_global_pool_hard_max_size(void) > -{ > #ifdef __linux__ > - g_autofree char *contents = NULL; > - int max_map_count; > +/* > + * include/linux/mm.h > + */ > +#define DEFAULT_MAX_MAP_COUNT 65530 > > - /* > - * 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)) { > +static unsigned int get_max_map_count(void) > +{ > + g_autofree char *contents = NULL; > + int max_map_count = 0; > + if (g_file_get_contents("/proc/sys/vm/max_map_count", &contents, > + NULL, NULL)) { > /* contents has trailing newline, remove it before conversion */ > g_strchomp(contents); > - if (qemu_strtoi(contents, NULL, 10, &max_map_count) != 0) { > - return UINT_MAX; > - } > - /* > - * This is an upper bound that avoids exceeding max_map_count. Leave a > - * fixed amount for non-coroutine users like library dependencies, > - * vhost-user, etc. Each coroutine takes up 2 VMAs so halve the > - * remaining amount. > - */ > - if (max_map_count > 5000) { > - return (max_map_count - 5000) / 2; > - } else { > - /* Disable the global pool but threads still have local pools */ > - return 0; > + if (qemu_strtoi(contents, NULL, 10, &max_map_count) == 0) { > + return max_map_count; > } > } > -#endif > + return 0; > +} I'm now realizing we could just return DEFAULT_MAX_MAP_COUNT here and removed the conditional in the caller. > > +/* > + * 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. > + */ > +static unsigned int get_global_pool_hard_max_size(void) > +{ > + /* > + * Read from /proc might fail due to mandatory access control (AppArmor, > + * SELinux, etc). Use the kernel's default in that case. > + */ > + int max_map_count = get_max_map_count(); > + if (!max_map_count) { > + max_map_count = DEFAULT_MAX_MAP_COUNT; > + } > + > + /* > + * This is an upper bound that avoids exceeding max_map_count. Leave a > + * fixed amount for non-coroutine users like library dependencies, > + * vhost-user, etc. Each coroutine takes up 2 VMAs so halve the > + * remaining amount. > + */ > + if (max_map_count > 5000) { > + return (max_map_count - 5000) / 2; > + } else { > + /* Disable the global pool but threads still have local pools */ > + return 0; > + } > +} > +#else > +static unsigned int get_global_pool_hard_max_size(void) > +{ > return UINT_MAX; > } > +#endif > > static void __attribute__((constructor)) qemu_coroutine_init(void) > { > > -- > 2.53.0 > With regards, Daniel -- |: https://berrange.com ~~ https://hachyderm.io/@berrange :| |: https://libvirt.org ~~ https://entangle-photo.org :| |: https://pixelfed.art/berrange ~~ https://fstop138.berrange.com :|