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Re: [Qemu-devel] [PATCH v2] rcu: reduce more than 7MB heap memory by mal
From: |
Stefan Hajnoczi |
Subject: |
Re: [Qemu-devel] [PATCH v2] rcu: reduce more than 7MB heap memory by malloc_trim() |
Date: |
Thu, 23 Nov 2017 11:19:43 +0000 |
User-agent: |
Mutt/1.9.1 (2017-09-22) |
On Thu, Nov 23, 2017 at 02:41:16PM +0800, Yang Zhong 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
>
> 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" >> $config_host_mak
malloc(3) is provided by glibc, not glib, so the name
CONFIG_NONGLIBMALLOC is confusing.
I suggest calling it CONFIG_MALLOC_TRIM instead:
# Even if malloc_trim() is available, these non-libc memory allocators
# do not support it.
if test "$tcmalloc" = "yes" || test "$jemalloc" = "yes" ; then
if test "$malloc_trim" = "yes" ; then
echo "Disabling malloc_trim with non-libc memory allocator"
fi
malloc_trim="no"
fi
if test "$malloc_trim" != "no" ; then
cat > $TMPC << EOF
#include <malloc.h>
int main(void) { malloc_trim(0); return 0; }
EOF
if compile_prog "" "" ; then
malloc_trim="yes"
else
malloc_trim="no"
fi
fi
...
if test "$malloc_trim" = "yes" ; then
echo "CONFIG_MALLOC_TRIM=y" >> $config_host_mak
fi
Then the code in rcu.c just has to #ifdef CONFIG_MALLOC_TRIM and there's
no need for Linux-specific checks. If other operating systems support
malloc_trim() then QEMU will use it by default.
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