Re: [Qemu-devel] [PATCH v2] rcu: reduce more than 7MB heap memory by malloc_trim()

[Marc-André Lureau]

Hi

On Thu, Nov 23, 2017 at 7:41 AM, Yang Zhong <address@hidden> wrote:
> Since there are some issues in memory alloc/free machenism
> in glibc for little chunk memory, if Qemu frequently
> alloc/free little chunk memory, the glibc doesn't alloc
> little chunk memory from free list of glibc and still
> allocate from OS, which make the heap size bigger and bigger.
>
> This patch introduce malloc_trim(), which will free heap memory.
>
> Below are test results from smaps file.
> (1)without patch
> 55f0783e1000-55f07992a000 rw-p 00000000 00:00 0  [heap]
> Size:              21796 kB
> Rss:               14260 kB
> Pss:               14260 kB
>
> (2)with patch
> 55cc5fadf000-55cc61008000 rw-p 00000000 00:00 0  [heap]
> Size:              21668 kB
> Rss:                6940 kB
> Pss:                6940 kB

Have you opened a bug to glibc malloc (or discussed that issue with
the glibc malloc developpers) ?

Or is there a justification that qemu should have its own trim
heuristic on top of malloc?

>
> Signed-off-by: Yang Zhong <address@hidden>
> ---
>  configure  | 4 ++++
>  util/rcu.c | 6 ++++++
>  2 files changed, 10 insertions(+)
>
> diff --git a/configure b/configure
> index 0e856bb..5b463d4 100755
> --- a/configure
> +++ b/configure
> @@ -6012,6 +6012,10 @@ if test "$opengl" = "yes" ; then
>    fi
>  fi
>
> +if test "$tcmalloc" = "yes" || test "$jemalloc" = "yes" ; then
> +  echo "CONFIG_NONGLIBMALLOC=y" >> $config_host_mak
> +fi
> +
>  if test "$avx2_opt" = "yes" ; then
>    echo "CONFIG_AVX2_OPT=y" >> $config_host_mak
>  fi
> diff --git a/util/rcu.c b/util/rcu.c
> index ca5a63e..f3e96a8 100644
> --- a/util/rcu.c
> +++ b/util/rcu.c
> @@ -32,6 +32,9 @@
>  #include "qemu/atomic.h"
>  #include "qemu/thread.h"
>  #include "qemu/main-loop.h"
> +#if defined(CONFIG_LINUX)
> +#include <malloc.h>
> +#endif
>
>  /*
>   * Global grace period counter.  Bit 0 is always one in rcu_gp_ctr.
> @@ -272,6 +275,9 @@ static void *call_rcu_thread(void *opaque)
>              node->func(node);
>          }
>          qemu_mutex_unlock_iothread();
> +#if defined(CONFIG_LINUX) && !defined(CONFIG_NONGLIBMALLOC)
> +        malloc_trim(4 * 1024 * 1024);
> +#endif
>      }
>      abort();
>  }
> --
> 1.9.1
>
>



-- 
Marc-André Lureau