On 06.07.21 15:02, Anand Babu wrote:
> Hi Centos Community,
>
> This is my first time here and I apologize in advance if I made a mistake
> here and hope you will correct me , if i made any.
>
>
> With that said,
>
> This is a native example that was written to narrow down the higher RAM
> usage that we see when we are using Centos8 as opposed to Centos7.
>
> The c-code is very small and looks like this :
>
> #include<stdio.h>
>
> #include<unistd.h>
>
> int main()
>
> {
>
> pause();
>
> return 0;
>
> }
>
> I compile and run the binary on centos7 and memory backed section of pmap
> output looks like below:
>
> pmap -X $(pidof sleep) | head -n -2 | awk '{ if (NR > 2 && $5 > 0 )
> printf "%12s %8s %8s %4s %s\n", $1, $6, $7, $2,$13}'
> 00400000 4 4 r-xp sleep
> 00600000 4 4 r--p sleep
> 00601000 4 4 rw-p sleep*7f54514f9000 1808
> 204 r-xp libc-2.17.so <http://libc-2.17.so>
> *7f54516bd000 2044 0 ---p libc-2.17.so
> 7f54518bc000 16 16 r--p libc-2.17.so
> 7f54518c0000 8 8 rw-p libc-2.17.so
> 7f54518c7000 136 108 r-xp ld-2.17.so
> 7f5451ae8000 4 4 r--p ld-2.17.so
> 7f5451ae9000 4 4 rw-p ld-2.17.so
>
> and ps says the following:
>
> ** ps -o rss= pidof sleep 352**
>
> Running the same binary on centos8 leads to
>
> ** ps -o rss= pidof pause 784 **
>
> and the pmap output looks like below:
>
> 00400000 4 4 r-xp pause
> 00600000 4 4 r--p pause
> 00601000 4 4 rw-p pause* 7f24029a8000 1776
> 788 r-xp libc-2.28.so <http://libc-2.28.so> *
> 7f2402b64000 2044 0 ---p libc-2.28.so
> 7f2402d63000 16 16 r--p libc-2.28.so
> 7f2402d67000 8 8 rw-p libc-2.28.so
> 7f2402d6d000 176 176 r-xp ld-2.28.so
> 7f2402f99000 4 4 r--p ld-2.28.so
> 7f2402f9a000 8 8 rw-p ld-2.28.so
>
> For running the same executable, the libc.so takes 788KB(204KB on centos7).
>
> Note:
>
> 1.
>
> This is not the only library that is showing this behavior, but we see
> the same behavior for other shared-library as well as executables that were
> compiled on centos7. Running the same executables/shared objects take a
> higher amount of pages on centos8 than on centos7.
> 2.
>
> Since the glibc version on Centos8 was 2.28 , i have compiled 2.17
> version and then used patchelf to patch the centos7 built binary to make
> use of 2.17 glibc on centos8 host like patchelf --set-interpreter
>
> /home/babu/RSS_measurement/2_17_downloaded/glibc_home/lib/ld-linux-x86-64.so.2
> --set-rpath /home/babu/RSS_measurement/2_17_downloaded/glibc_home/lib
> /tmp/pause
>
> and then run it under LD_DEBUG=libs and verified the 2.17 version of libc
> libraries were used and still the memory usage on centos8 was higher than
> on centos7 (about the same numbers as above).
>
> What could be the reason for the higher RAM usage on centos8 vs centos7? I
> can imagine some defaults have changed on centos8 and that has meant this
> impact and i could change this default and could reproduce the same RSS
> numbers on centos8 as well?
>
>
How does the results look like after doing:
echo never > /sys/kernel/mm/transparent_hugepage/enabled
--
Leon