Hi all, I was wondering if someone could help me out with trying to understand what’s gong on with an MPI_Waitall() call with regards to resident set memory usage. Platform information at the end of the email. If I run a 4 process MPI job on my desktop machine, I get a steady increase in memory usage over the course of the program. Apart from the places where I would reasonably expect expect memory usage to increase, I also see regular increases when I call MPI_Waitall(). I measure this behavior via: getmem( &rss0, &vs ); result = MPI_Waitall( n_buffer_reqs, buffer_reqs, MPI_STATUSES_IGNORE ); if( result != MPI_SUCCESS ) ERROR_MACRO( "MPI_Waitall" ); getmem( &rss1, &vs ); … where getmem() queries the OS kernel to return the resident set size (“rss") and virtual memory size (“vs", ignored). The getmem() function does not allocate any memory itself, so I can hopefully see any difference in the resident set memory used before and after the MPI_Waitall() call via (rss1-rss0). After MPI_Waitall() returns, I very often see an increase in the resident set size ranging from 4096 bytes to 65536 bytes. Running an “identical” 4-process job on a single node of the Blue Waters compute cluster (Cray XE system, GCC 4.8.1, Cray mpich 6.0.1) does not seem to produce this behaviour. Switching the MPI_Waitall() for a loop over MPI_Waitany() calls also produces resident set increases. Does anyone have any comments or suggestions as to how I might understand whether this behavior is errant, and how I might track down the cause? It’s irritating me as I’d really like to produce code with as low a memory overhead as possible! Cheers, J. ------------------ Platform info: ------------------ OS: Apple OSX 10.9.1 mpicxx —version: Apple LLVM version 5.0 (clang-500.2.79) (based on LLVM 3.3svn) Target: x86_64-apple-darwin13.0.0 Thread model: posix mpiexec —version HYDRA build details: Version: 3.0.4 Release Date: Wed Apr 24 10:08:10 CDT 2013 CC: /usr/bin/clang -pipe -arch x86_64 -Wl,-headerpad_max_install_names -arch x86_64 CXX: /usr/bin/clang++ -pipe -arch x86_64 -Wl,-headerpad_max_install_names -arch x86_64 F77: /opt/local/bin/gfortran-mp-4.8 -pipe -m64 -Wl,-headerpad_max_install_names -arch x86_64 F90: /opt/local/bin/gfortran-mp-4.8 -pipe -m64 -Wl,-headerpad_max_install_names -arch x86_64 Configure options: '--disable-option-checking' '--prefix=/opt/local' '--disable-dependency-tracking' '--disable-silent-rules' '--enable-base-cache' '--enable-cache' '--enable-cxx' '--enable-fast=O2' '--enable-shared' '--enable-smpcoll' '--with-device=ch3:nemesis' '--with-pm=hydra' '--with-thread-package=posix' '--enable-versioning' 'F90FLAGS=' 'F90=' '--enable-timer-type=mach_absolute_time' '--libdir=/opt/local/lib/mpich-mp' '--sysconfdir=/opt/local/etc/mpich-mp' '--program-suffix=-mp' '--enable-f77' '--enable-fc' 'CC=/usr/bin/clang' 'CFLAGS=-pipe -arch x86_64 -O2' 'LDFLAGS=-Wl,-headerpad_max_install_names -arch x86_64 ' 'CXX=/usr/bin/clang++' 'CXXFLAGS=-pipe -arch x86_64 -O2' 'F77=/opt/local/bin/gfortran-mp-4.8' 'FFLAGS=-pipe -m64 -O2' 'FC=/opt/local/bin/gfortran-mp-4.8' 'FCFLAGS=-pipe -m64 -O2' '--cache-file=/dev/null' '--srcdir=.' 'LIBS=-lpthread ' 'CPPFLAGS= -I/opt/local/var/macports/build/_opt_mports_dports_science_mpich/mpich-default/work/mpich-3.0.4/src/mpl/include -I/opt/local/var/macports/build/_opt_mports_dports_science_mpich/mpich-default/work/mpich-3.0.4/src/mpl/include -I/opt/local/var/macports/build/_opt_mports_dports_science_mpich/mpich-default/work/mpich-3.0.4/src/openpa/src -I/opt/local/var/macports/build/_opt_mports_dports_science_mpich/mpich-default/work/mpich-3.0.4/src/openpa/src -I/opt/local/var/macports/build/_opt_mports_dports_science_mpich/mpich-default/work/mpich-3.0.4/src/mpi/romio/include' Process Manager: pmi Launchers available: ssh rsh fork slurm ll lsf sge manual persist Topology libraries available: hwloc Resource management kernels available: user slurm ll lsf sge pbs cobalt Checkpointing libraries available: Demux engines available: poll select