From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:60505) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1eGmqn-0005Vg-7Z for qemu-devel@nongnu.org; Mon, 20 Nov 2017 09:15:11 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1eGmqi-0005t2-Tc for qemu-devel@nongnu.org; Mon, 20 Nov 2017 09:15:05 -0500 Received: from mx1.redhat.com ([209.132.183.28]:40956) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1eGmqi-0005sN-KA for qemu-devel@nongnu.org; Mon, 20 Nov 2017 09:15:00 -0500 Date: Mon, 20 Nov 2017 14:14:50 +0000 From: "Daniel P. Berrange" Message-ID: <20171120141450.GL31943@redhat.com> Reply-To: "Daniel P. Berrange" References: <1510899814-19372-1-git-send-email-yang.zhong@intel.com> <20171117135409.GA3669@stefanha-x1.localdomain> <20171117140620.GS25830@redhat.com> <20171120085442.GB6622@yangzhon-Virtual> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20171120085442.GB6622@yangzhon-Virtual> 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: Zhong Yang Cc: qemu-devel@nongnu.org, pbonzini@redhat.com, stefanha@redhat.com, anthony.xu@intel.com, stone.xulei@huawei.com, arei.gonglei@huawei.com, wangxinxin.wang@huawei.com, weidong.huang@huawei.com, zhang.zhanghailiang@huawei.com, liujunjie23@huawei.com On Mon, Nov 20, 2017 at 04:54:42PM +0800, Zhong Yang wrote: > On Fri, Nov 17, 2017 at 02:06:20PM +0000, Daniel P. Berrange wrote: > > 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. > > In fact, i firstly adopted mallopt() solution to optimize the heap memory, > but i found this function is NOT useful, which are difference with MAN's > description, so i had to swith to use malloc_trim(). > > Also, how does malloc_trim interact with tcmalloc.so that people often > > use in preference to glibc's built in malloc ? > Thanks, you reminded me to consider tcmalloc or jemalloc. > > Whether below code is more suitable? thanks! > #if defined(CONFIG_LINUX) && defined(__GLIBC__) > malloc_trim(0); > #endif Both of those macro symbols will still be defined even when tcmalloc/jemalloc are in use. I wonder if tcmalloc/jemalloc even suffer from the same problem that libc's builtin malloc has ? 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 :|