Fix MPI_Alloc_mem's size and report failure by pera-noaa · Pull Request #534 · mpickpt/mana

pera-noaa · 2026-10-20T07:25:22Z

MPI_Alloc_mem allocated size * sizeof(MPI_Aint) bytes, eight times the request, and returned MPI_SUCCESS when malloc failed. This allocates size bytes and returns MPI_ERR_NO_MEM when malloc fails.

misc_calls now checks that a 64 MiB MPI_Alloc_mem grows the process by less than twice that. On Hercules (Intel MPI 2021.7.1, 2 ranks on 2 nodes, dmtcp/dmtcp#1303 applied to avoid #523), main fails ("grew the process by 536875008 bytes"), this branch passes, and so does the native run. The suite passes 22 of 23 in both modes, the same as main: attributes fails there for #524. Requests that reach past the lower half still crash (#533).

🤖 Generated with Claude Code

Summary by CodeRabbit

Bug Fixes
- Corrected MPI_Alloc_mem to allocate the requested number of bytes rather than excessive memory.
- Allocation failures for positive-size requests now return an appropriate MPI memory error instead of leaving the result unchecked.
- Improved memory usage behavior for large allocations, reducing unnecessary virtual memory consumption.
Tests
- Added coverage for large memory allocations, successful cleanup, failure handling, and virtual memory growth.

MPI_Alloc_mem allocated size * sizeof(MPI_Aint) bytes, eight times the request, and returned MPI_SUCCESS when malloc failed. Allocate size bytes, and return MPI_ERR_NO_MEM when malloc fails. misc_calls now checks that a 64 MiB MPI_Alloc_mem grows the process by less than twice that. Co-Authored-By: Claude <noreply@anthropic.com>

coderabbitai · 2026-10-20T07:25:37Z

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Reviewing files that changed from the base of the PR and between c7e45c1 and 2b9495e.

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mpi-proxy-split/mpi-wrappers/mpi_win_wrappers.cpp
mpi-proxy-split/test/misc_calls.c

📝 Walkthrough

PMPI_Alloc_mem now allocates the requested byte count and reports allocation failure for positive sizes. The misc calls test checks virtual-memory growth for a 64 MiB startup allocation.

Changes: MPI allocation size correction

Layer / File(s)	Summary
Allocation size and regression check `mpi-proxy-split/mpi-wrappers/mpi_win_wrappers.cpp`, `mpi-proxy-split/test/misc_calls.c`	`PMPI_Alloc_mem` allocates the requested byte count and returns `MPI_ERR_NO_MEM` if a positive-size allocation fails. The test measures `VmSize` before and after a 64 MiB startup allocation, checks the allocation and growth, then frees the buffer.

Priority: ⬇️ Low

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Bug fix

Suggested reviewers: xuyao00

Merge Risk: 🔵 Low · up to c7e45

The allocation fix is mergeable with a bounded test gap: an unavailable memory reading can let the regression check pass incorrectly. Validate both readings to make the check reliable.

Pre-merge checks: 4 · 1

Failed checks: 1 warning

Check name	Status	Explanation	Resolution
Docstring Coverage		Docstring coverage is 25.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 4 functions across 2 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

Passed checks: 4 passed

Check name	Status	Explanation
Description Check		Check skipped - CodeRabbit’s high-level summary is enabled.
Title check		The title clearly and concisely describes the main changes: correcting the allocation size and reporting allocation failure in MPI_Alloc_mem.
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.

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Actionable comments posted: 1

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Inline comments:
Review comments at @mpi-proxy-split/test/misc_calls.c:
- Line 177: Update the memory-growth check around vm_size_kb() to store the
second reading separately, then require both before and after readings to be
nonnegative before accepting grown; preserve the existing allocation and
upper-bound checks.

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mpi-proxy-split/mpi-wrappers/mpi_win_wrappers.cpp
mpi-proxy-split/test/misc_calls.c

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xuyao00

I checked these against MPICH 5.0.1 (source and a native run).

xuyao00 · 2026-10-20T17:30:13Z

+  void *mem = malloc(size);
+  if (mem == NULL && size > 0) {


A negative size still returns MPI_SUCCESS: malloc((size_t)-1) returns NULL, and size > 0 skips the error, so the caller gets a NULL buffer and no error. MPICH 5.0.1 rejects a negative size in its argument checks (MPIR_ERRTEST_ARGNEG(size, ...) in internal_Alloc_mem) with error class MPI_ERR_ARG, and leaves baseptr unchanged. Suggest:

Suggested change

void *mem = malloc(size);

if (mem == NULL && size > 0) {

if (size < 0) {

return MPI_ERR_ARG;

}

void *mem = malloc(size);

if (mem == NULL && size > 0) {

xuyao00 · 2026-10-20T17:30:13Z

+  long grown = (vm_size_kb() - before) * 1024;
+  MT_CHECK(large != NULL && grown < 2 * LARGE, "MPI_Alloc_mem(%ld) grew the"
+           " process by %ld bytes", LARGE, grown);


Besides the -1 readings CodeRabbit pointed out, the check has no lower bound, so an MPI_Alloc_mem that allocates less than LARGE also passes. Requiring grown >= LARGE works under MANA too: glibc serves 64 MiB with mmap, and the lower half's __mmap_wrapper maps it into an unmapped gap, so VmSize grows by at least LARGE.

Suggested change

long grown = (vm_size_kb() - before) * 1024;

MT_CHECK(large != NULL && grown < 2 * LARGE, "MPI_Alloc_mem(%ld) grew the"

" process by %ld bytes", LARGE, grown);

long after = vm_size_kb();

long grown = (after - before) * 1024;

MT_CHECK(large != NULL && before > 0 && after > 0 && grown >= LARGE &&

grown < 2 * LARGE, "MPI_Alloc_mem(%ld) grew the process by %ld"

" bytes", LARGE, grown);

xuyao00 · 2026-10-20T17:30:13Z

+  long grown = (vm_size_kb() - before) * 1024;
+  MT_CHECK(large != NULL && grown < 2 * LARGE, "MPI_Alloc_mem(%ld) grew the"
+           " process by %ld bytes", LARGE, grown);
+  MT_MPI(MPI_Free_mem(large));


If the wrapper rejects a negative size (see the comment on mpi_win_wrappers.cpp), a case here would keep it covered. Natively it needs MPI_ERRORS_RETURN first: MPICH raises the error through the handler on MPI_COMM_SELF (then MPI_COMM_WORLD), and the default handler aborts. It should also compare the error class, because MPICH returns an error code, not the bare class. Something like (not run under MANA):

MT_MPI(MPI_Comm_set_errhandler(MPI_COMM_SELF, MPI_ERRORS_RETURN)); void *bad = NULL; int rc = MPI_Alloc_mem(-1, MPI_INFO_NULL, &bad); int cls = MPI_SUCCESS; MT_MPI(MPI_Error_class(rc, &cls)); MT_CHECK(cls == MPI_ERR_ARG, "MPI_Alloc_mem(-1) returned class %d", cls);

xuyao00

See comments

…m below MPICH returns MPI_ERR_ARG for a negative size and leaves baseptr unchanged; the wrapper now does too. misc_calls checks that case, and that the large buffer grows the process by at least its size. It sets MPI_ERRORS_RETURN on both MPI_COMM_SELF and MPI_COMM_WORLD: an MPI 4 library raises the error on the first, an MPI 3 one (Intel MPI 2021) on the second.

pera-noaa · 2026-10-20T19:10:48Z

Done in 2b9495e. One change: Intel MPI 2021 (MPI 3) raises the error on MPI_COMM_WORLD, so the test sets MPI_ERRORS_RETURN on both communicators. Passes natively and under MANA; fails without the check or with half the allocation.

xuyao00

LGTM

coderabbitai Bot reviewed Oct 20, 2026

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Comment thread mpi-proxy-split/test/misc_calls.c Resolved

xuyao00 reviewed Oct 20, 2026

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xuyao00 approved these changes Oct 20, 2026

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xuyao00 merged commit d291f1b into mpickpt:main Oct 20, 2026
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Fix MPI_Alloc_mem's size and report failure - #534

Fix MPI_Alloc_mem's size and report failure#534
xuyao00 merged 2 commits into
mpickpt:mainfrom
pera-noaa:alloc-mem

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-  long grown = (vm_size_kb() - before) * 1024;
-  MT_CHECK(large != NULL && grown < 2 * LARGE, "MPI_Alloc_mem(%ld) grew the"
-           " process by %ld bytes", LARGE, grown);
+  long after = vm_size_kb();
+  long grown = (after - before) * 1024;
+  MT_CHECK(large != NULL && before > 0 && after > 0 && grown >= LARGE &&
+           grown < 2 * LARGE, "MPI_Alloc_mem(%ld) grew the process by %ld"
+           " bytes", LARGE, grown);

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pera-noaa commented Oct 20, 2026 •

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