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 <malloc.h> > > > > 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. Hello Daniel,
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(). Regards, Yang > 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 Regards, Yang > > 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 :|