From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:39178) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1eFhHw-0001OL-6V for qemu-devel@nongnu.org; Fri, 17 Nov 2017 09:06:42 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1eFhHs-0001n9-68 for qemu-devel@nongnu.org; Fri, 17 Nov 2017 09:06:36 -0500 Received: from mx1.redhat.com ([209.132.183.28]:37390) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1eFhHs-0001lN-0D for qemu-devel@nongnu.org; Fri, 17 Nov 2017 09:06:32 -0500 Date: Fri, 17 Nov 2017 14:06:20 +0000 From: "Daniel P. Berrange" Message-ID: <20171117140620.GS25830@redhat.com> Reply-To: "Daniel P. Berrange" References: <1510899814-19372-1-git-send-email-yang.zhong@intel.com> <20171117135409.GA3669@stefanha-x1.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20171117135409.GA3669@stefanha-x1.localdomain> Subject: Re: [Qemu-devel] [PATCH] rcu: reduce half heap memory size by malloc_trim() List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Stefan Hajnoczi Cc: Yang Zhong , weidong.huang@huawei.com, zhang.zhanghailiang@huawei.com, liujunjie23@huawei.com, wangxinxin.wang@huawei.com, stone.xulei@huawei.com, qemu-devel@nongnu.org, anthony.xu@intel.com, arei.gonglei@huawei.com, pbonzini@redhat.com On Fri, Nov 17, 2017 at 01:54:09PM +0000, Stefan Hajnoczi wrote: > On Fri, Nov 17, 2017 at 02:23:34PM +0800, Yang Zhong wrote: > > diff --git a/util/rcu.c b/util/rcu.c > > index ca5a63e..8d491a6 100644 > > --- a/util/rcu.c > > +++ b/util/rcu.c > > @@ -26,6 +26,7 @@ > > * IBM's contributions to this file may be relicensed under LGPLv2 or later. > > */ > > > > +#include > > This header file is not mentioned in the C99 standard or POSIX. It is > probably not available on all host OSes that QEMU supports. Please use > #ifdef CONFIG_LINUX. > > > #include "qemu/osdep.h" > > #include "qemu-common.h" > > #include "qemu/rcu.h" > > @@ -272,6 +273,9 @@ static void *call_rcu_thread(void *opaque) > > node->func(node); > > } > > qemu_mutex_unlock_iothread(); > > +#ifdef CONFIG_LINUX > > + malloc_trim(0); > > +#endif > > It is important that the rcu thread isn't overzealous in minimizing heap > size if that means ordinary malloc(3) calls will experience latency > spikes. Please leave a few MB free so that malloc(3) doesn't take the > slow path. If you pass '0' the docs say that the minimum amount is left in the heap, per M_TOP_PAD, which is 128kb. Strangely the mallopt(3) man page suggests, that free() should automatically trim the heap when its size exceeds M_TOP_TRIM, which is again 128kb by default. So I'm puzzelled by malloc_trim() would be needed unless there are scenarios in which free() won't trim, that aren't mentioned in the manpage. Also, how does malloc_trim interact with tcmalloc.so that people often use in preference to glibc's built in malloc ? 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 :|