Re: [LTP] [PATCH v7 3/4] Hugetlb: Migrating libhugetlbfs chunk-overcommit

Cyril Hrubis
2022-11-04T12:11:15Z

Hi!
> diff --git a/testcases/kernel/mem/hugetlb/hugemmap/hugemmap08.c b/testcases/kernel/mem/hugetlb/hugemmap/hugemmap08.c
> new file mode 100644
> index 000000000..3efabc4aa
> --- /dev/null
> +++ b/testcases/kernel/mem/hugetlb/hugemmap/hugemmap08.c
> @@ -0,0 +1,146 @@
> +// SPDX-License-Identifier: LGPL-2.1-or-later
> +/*
> + * Copyright (C) 2005-2006 David Gibson & Adam Litke, IBM Corporation.
> + * Author: David Gibson & Adam Litke
> + */
> +
> +/*\
> + * [Description]
> + *
> + * Some kernel versions after hugepage demand allocation was added used a
> + * dubious heuristic to check if there was enough hugepage space available
> + * for a given mapping. The number of not-already-instantiated pages in
> + * the mapping was compared against the total hugepage free pool. It was
> + * very easy to confuse this heuristic into overcommitting by allocating
> + * hugepage memory in chunks, each less than the total available pool size
> + * but together more than available. This would generally lead to OOM
> + * SIGKILLs of one process or another when it tried to instantiate pages
> + * beyond the available pool.
> + *
> + * HISTORY

This looks like a leftover.

> + *
> + */
> +
> +#define _GNU_SOURCE
> +#include <stdio.h>
> +#include <stdlib.h>
> +#include <sys/mount.h>
> +#include <limits.h>
> +#include <sys/param.h>
> +#include <sys/types.h>
> +#include <sys/wait.h>
> +#include <signal.h>
> +
> +#include "hugetlb.h"
> +
> +#define MNTPOINT "hugetlbfs/"
> +#define WITH_OVERCOMMIT 0
> +#define WITHOUT_OVERCOMMIT 1
> +
> +static long hpage_size;
> +static int huge_fd = -1;
> +
> +static void test_chunk_overcommit(void)
> +{
> + unsigned long totpages, chunk1, chunk2;
> + void *p, *q;
> + pid_t child;
> + int status;
> +
> + totpages = SAFE_READ_MEMINFO(MEMINFO_HPAGE_FREE);
> +
> + chunk1 = (totpages / 2) + 1;
> + chunk2 = totpages - chunk1 + 1;
> +
> + tst_res(TINFO, "Free: %ld hugepages available: "
> + "chunk1=%ld chunk2=%ld", totpages, chunk1, chunk2);
> +
> + p = SAFE_MMAP(NULL, chunk1*hpage_size, PROT_READ|PROT_WRITE, MAP_SHARED,
> + huge_fd, 0);
> +
> + q = mmap(NULL, chunk2*hpage_size, PROT_READ|PROT_WRITE, MAP_SHARED,
> + huge_fd, chunk1*hpage_size);
> + if (q == MAP_FAILED) {
> + if (errno != ENOMEM) {
> + tst_res(TFAIL | TERRNO, "mmap() chunk2");
> + goto cleanup1;
> + } else {
> + tst_res(TPASS, "Successful without overcommit pages");
> + goto cleanup1;
> + }
> + }
> +
> + tst_res(TINFO, "Looks like we've overcommitted, testing...");
> + /* Looks like we're overcommited, but we need to confirm that
> + * this is bad. We touch it all in a child process because an
> + * overcommit will generally lead to a SIGKILL which we can't
> + * handle, of course.
> + */
> + child = SAFE_FORK();
> +
> + if (child == 0) {
> + memset(p, 0, chunk1*hpage_size);
> + memset(q, 0, chunk2*hpage_size);
> + exit(0);
> + }
> +
> + SAFE_WAITPID(child, &status, 0);
> +
> + if (WIFSIGNALED(status)) {
> + tst_res(TFAIL, "Killed by signal '%s' due to overcommit",
> + tst_strsig(WTERMSIG(status)));
> + goto cleanup2;
> + }
> +
> + tst_res(TPASS, "Successful with overcommit pages");
> +
> +cleanup2:
> + SAFE_MUNMAP(q, chunk2*hpage_size);
> +
> +cleanup1:
> + SAFE_MUNMAP(p, chunk1*hpage_size);
> + SAFE_FTRUNCATE(huge_fd, 0);
> +}
> +
> +static void run_test(unsigned int test_type)
> +{
> + switch (test_type) {
> + case WITHOUT_OVERCOMMIT:
> + tst_res(TINFO, "Without overcommit testing...");
> + SAFE_FILE_PRINTF(PATH_OC_HPAGES, "%d", 0);
> + break;
> + case WITH_OVERCOMMIT:
> + tst_res(TINFO, "With overcommit testing...");
> + SAFE_FILE_PRINTF(PATH_OC_HPAGES, "%d", 2);
> + break;
> + }
> + test_chunk_overcommit();
> +}
> +
> +static void setup(void)
> +{
> + hpage_size = SAFE_READ_MEMINFO(MEMINFO_HPAGE_SIZE)*1024;
> + huge_fd = tst_creat_unlinked(MNTPOINT);

Shouldn't we open a file under the MNTPOINT?

Something as:

#define HUGEFILE MNTPOINT "hugefile"

...
huge_fd = tst_creat_unlinked(HUGEFILE);
...

The rest looks good to me.

--
Cyril Hrubis
chrubis@suse.cz