The upper limit has not changed by more than one bit (102X to 204X) in as long as I have been paying attention. There is a need to keep the bits in (comm,tag,rank) small, although I don't know the details in MPICH but the issue was discussed in https://cug.org/5-publications/proceedings_attendee_lists/CUG09CD/S09_Procee... . A better option for RMA programs is to provide a window info key to disable the duplicating of communicators for every window. This would force the implementation to generate them on-the-fly for window collectives (e.g. MPI_Win_fence and MPI_Win_free) but there are many RMA programs that do not use MPI_Win_fence (the most reasonable use of RMA is passive target with flush synchronization, which is non-collective). If MPI_Win_free is on the critical path, the application is poorly written. Jeff On Mon, Sep 19, 2016 at 11:15 AM, Marvin Smith <[email protected]> wrote:

Thanks for the quick reply. Do you see this value increasing in the future? In the meantime, I have a solution with less windows.

Thanks, Marvin

From: "Oden, Lena" <[email protected]> To: "[email protected]" <[email protected]> Date: 09/19/2016 11:11 AM Subject: Re: [mpich-discuss] MPI Window limit on mpich ------------------------------

Hi Marvin,

currently, this is a limitation inside MPICH. For every new window, MPICH internally creates a new communicator - for every communicator a new (unique) context ID is required - and the number of different context IDs is limited to 2048.

This context-id/ communicator is required for internal synchronization (e.g. barriers) . We have to ensure, that his communication is not interfering with other communication on other windows or communicators.

If you use more communicators, you should run into this problem earlier, because you already create other communicators (the limit is per process)

Lena

On Sep 19, 2016, at 12:49 PM, Marvin Smith <*[email protected]* <[email protected]>> wrote:

Good morning,

I wanted to present an issue I am having with MPICH and validate whether this is a configuration problem, a limitation with MPICH, or a bug.

I am writing an application which uses a large number of MPI windows, each window is given a relatively large amount of memory. This has never been a problem before, however we discovered if you allocate more than 2045 windows, you get an exception thrown.

Notes:

- I am compiling using g++, version 4.8.5 on Red Hat Enterprise Linux version 7.2. - My MPICH version is listed at the bottom of this email. It was installed via yum and is the RHEL default. - I have attached sample output, to include the stdout/stderr. Also included is a Makefile and a simple example. - The boundary of failure is between 2045 and 2046 windows. - I have verified on my system this problem repeats even if I distribute windows between multiple communicators. - I have not tested yet against ompi or mvapich.

#----------------------------------------------------------- ------------------------------------# #- Here is my output -# #----------------------------------------------------------- ------------------------------------#

mpirun -np 2 -hosts localhost ./mpi-win-test 2046 1 Initialized Rank: 0, Number Processors: 2, Hostname: test-machine Initialized Rank: 1, Number Processors: 2, Hostname: test-machine Fatal error in MPI_Win_create_dynamic: Other MPI error, error stack: MPI_Win_create_dynamic(154)..........: MPI_Win_create_dynamic(MPI_INFO_NULL, MPI_COMM_WORLD, win=0x10c1464) failed MPID_Win_create_dynamic(139).........: win_init(254)........................: MPIR_Comm_dup_impl(55)...............: MPIR_Comm_copy(1552).................: MPIR_Get_contextid(799)..............: MPIR_Get_contextid_sparse_group(1146): Cannot allocate context ID because of fragmentation (0/2048 free on this process; ignore_id=0) Fatal error in MPI_Win_create_dynamic: Other MPI error, error stack: MPI_Win_create_dynamic(154)..........: MPI_Win_create_dynamic(MPI_INFO_NULL, MPI_COMM_WORLD, win=0x19ef444) failed MPID_Win_create_dynamic(139).........: win_init(254)........................: MPIR_Comm_dup_impl(55)...............: MPIR_Comm_copy(1552).................: MPIR_Get_contextid(799)..............: MPIR_Get_contextid_sparse_group(1146): Cannot allocate context ID because of fragmentation (0/2048 free on this process; ignore_id=0)

============================================================ ======================= = BAD TERMINATION OF ONE OF YOUR APPLICATION PROCESSES = EXIT CODE: 1 = CLEANING UP REMAINING PROCESSES = YOU CAN IGNORE THE BELOW CLEANUP MESSAGES ============================================================ ======================= make: *** [run] Error 1

* #------------------------------------------------------------------------------------------#* * #- Here is my Sample Makefile -#* * #------------------------------------------------------------------------------------------#*

# Path to mpich on RHEL7 MPI_INCL=-I/usr/include/mpich-x86_64 MPI_LIBS=-L/usr/lib64/mpich/lib -lmpich

# C++11 Bindings (Being lazy with string) CXX_ARGS=-std=c++11

# Make th test all: mpi-win-test

mpi-win-test: mpi-win-test.cpp g++ $< -o $@ $(MPI_INCL) $(MPI_LIBS) $(CXX_ARGS)

# Args for application NUM_WINDOWS=2046 USE_DYNAMIC=1

# Sample run usage # # Args: # - Number of Windows # - Type of windows (1 dynamic, 0 static) run: mpirun -np 2 -hosts localhost ./mpi-win-test $(NUM_WINDOWS) $(USE_DYNAMIC)

* #------------------------------------------------------------------------------------------#* * #- Here is my Sample Application -#* * #------------------------------------------------------------------------------------------#*

#include <mpi.h>

#include <iostream> #include <string> #include <vector>

using namespace std;

int main( int argc, char* argv[] ) { // Number of MPI Windows int num_windows = std::stoi(argv[1]);

bool use_dynamic = std::stoi(argv[2]);

// Initialize MPI MPI_Init( &argc, &argv );

// Get the rank and size int rank, nprocs; MPI_Comm_size( MPI_COMM_WORLD, &nprocs ); MPI_Comm_rank( MPI_COMM_WORLD, &rank );

// Get the processor name char hostname[MPI_MAX_PROCESSOR_NAME]; int hostname_len; MPI_Get_processor_name( hostname, &hostname_len);

// Print Message for( int i=0; i<nprocs; i++ ){ MPI_Barrier(MPI_COMM_WORLD); if( i == rank ){ std::cout << "Initialized Rank: " << rank << ", Number Processors: " << nprocs << ", Hostname: " << hostname << std::endl; } }

// MPI Variables vector<MPI_Aint> sdisp_remotes(num_windows); vector<MPI_Aint> sdisp_locals(num_windows);

// Create MPI Windows vector<MPI_Win> windows(num_windows);

int64_t buffer_size = 1000; char* buffer = new char[buffer_size];

for( int i=0; i<num_windows; i++ ) { if( use_dynamic ) { MPI_Win_create_dynamic( MPI_INFO_NULL, MPI_COMM_WORLD, &windows[i] ); }

else { MPI_Win_create( &buffer, buffer_size, 1, MPI_INFO_NULL, MPI_COMM_WORLD, &windows[i] ); } }

// Exception always occurs prior to reaching this point.

// More Code Here that I am removing for brevity

// Wait at the barrier MPI_Barrier( MPI_COMM_WORLD );

// Remove all windows for( int i=0; i<num_windows; i++) { // Destroy the MPI Window MPI_Win_free( &windows[i] ); } windows.clear();

// Clear buffer delete [] buffer; buffer = nullptr;

// Close MPI MPI_Finalize();

return 0; }

* #--------------------------------------------------------------------------#* * #- MPICH Version Output -#* * #--------------------------------------------------------------------------#* MPICH Version: 3.0.4 MPICH Release date: Wed Apr 24 10:08:10 CDT 2013 MPICH Device: ch3:nemesis MPICH configure: --build=x86_64-redhat-linux-gnu --host=x86_64-redhat-linux-gnu --program-prefix= --disable-dependency-tracking --prefix=/usr --exec-prefix=/usr --bindir=/usr/bin --sbindir=/usr/sbin --sysconfdir=/etc --datadir=/usr/share --includedir=/usr/include --libdir=/usr/lib64 --libexecdir=/usr/libexec --localstatedir=/var --sharedstatedir=/var/lib --mandir=/usr/share/man --infodir=/usr/share/info --enable-sharedlibs=gcc --enable-shared --enable-lib-depend --disable-rpath --enable-fc --with-device=ch3:nemesis --with-pm=hydra:gforker --sysconfdir=/etc/mpich-x86_64 --includedir=/usr/include/mpich-x86_64 --bindir=/usr/lib64/mpich/bin --libdir=/usr/lib64/mpich/lib --datadir=/usr/share/mpich --mandir=/usr/share/man/mpich --docdir=/usr/share/mpich/doc --htmldir=/usr/share/mpich/doc --with-hwloc-prefix=system FC=gfortran F77=gfortran CFLAGS=-m64 -O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector-strong --param=ssp-buffer-size=4 -grecord-gcc-switches -m64 -mtune=generic -fPIC CXXFLAGS=-m64 -O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector-strong --param=ssp-buffer-size=4 -grecord-gcc-switches -m64 -mtune=generic -fPIC FCFLAGS=-m64 -O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector-strong --param=ssp-buffer-size=4 -grecord-gcc-switches -m64 -mtune=generic -fPIC FFLAGS=-m64 -O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector-strong --param=ssp-buffer-size=4 -grecord-gcc-switches -m64 -mtune=generic -fPIC LDFLAGS=-Wl,-z,noexecstack MPICH2LIB_CFLAGS=-O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector-strong --param=ssp-buffer-size=4 -grecord-gcc-switches -m64 -mtune=generic MPICH2LIB_CXXFLAGS=-O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector-strong --param=ssp-buffer-size=4 -grecord-gcc-switches -m64 -mtune=generic MPICH2LIB_FCFLAGS=-O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector-strong --param=ssp-buffer-size=4 -grecord-gcc-switches -m64 -mtune=generic MPICH2LIB_FFLAGS=-O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector-strong --param=ssp-buffer-size=4 -grecord-gcc-switches -m64 -mtune=generic MPICH CC: cc -m64 -O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector-strong --param=ssp-buffer-size=4 -grecord-gcc-switches -m64 -mtune=generic -fPIC -O2 MPICH CXX: c++ -m64 -O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector-strong --param=ssp-buffer-size=4 -grecord-gcc-switches -m64 -mtune=generic -fPIC -O2 MPICH F77: gfortran -m64 -O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector-strong --param=ssp-buffer-size=4 -grecord-gcc-switches -m64 -mtune=generic -fPIC -O2 MPICH FC: gfortran -m64 -O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector-strong --param=ssp-buffer-size=4 -grecord-gcc-switches -m64 -mtune=generic -fPIC -O2 CONFIDENTIALITY NOTICE - SNC EMAIL: This email and any attachments are confidential, may contain proprietary, protected, or export controlled information, and are intended for the use of the intended recipients only. 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