Re: [LTP] [PATCH v3 3/4] Hugetlb: Migrating libhugetlbfs chunk-overcommit

Li Wang
2022-10-31T07:35:14Z

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On Sat, Oct 29, 2022 at 3:14 PM Tarun Sahu <tsahu@linux.ibm.com> wrote:

> Migrating the libhugetlbfs/testcases/chunk-overcommit.c test
>
> Test 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.
>
> Signed-off-by: Tarun Sahu <tsahu@linux.ibm.com>
> ---
> runtest/hugetlb | 1 +
> testcases/kernel/mem/.gitignore | 1 +
> .../kernel/mem/hugetlb/hugemmap/hugemmap08.c | 144 ++++++++++++++++++
> 3 files changed, 146 insertions(+)
> create mode 100644 testcases/kernel/mem/hugetlb/hugemmap/hugemmap08.c
>
> diff --git a/runtest/hugetlb b/runtest/hugetlb
> index f7ff81cb3..664f18827 100644
> --- a/runtest/hugetlb
> +++ b/runtest/hugetlb
> @@ -4,6 +4,7 @@ hugemmap04 hugemmap04
> hugemmap05 hugemmap05
> hugemmap06 hugemmap06
> hugemmap07 hugemmap07
> +hugemmap08 hugemmap08
> hugemmap05_1 hugemmap05 -m
> hugemmap05_2 hugemmap05 -s
> hugemmap05_3 hugemmap05 -s -m
> diff --git a/testcases/kernel/mem/.gitignore
> b/testcases/kernel/mem/.gitignore
> index df5256ec8..003ce422b 100644
> --- a/testcases/kernel/mem/.gitignore
> +++ b/testcases/kernel/mem/.gitignore
> @@ -5,6 +5,7 @@
> /hugetlb/hugemmap/hugemmap05
> /hugetlb/hugemmap/hugemmap06
> /hugetlb/hugemmap/hugemmap07
> +/hugetlb/hugemmap/hugemmap08
> /hugetlb/hugeshmat/hugeshmat01
> /hugetlb/hugeshmat/hugeshmat02
> /hugetlb/hugeshmat/hugeshmat03
> diff --git a/testcases/kernel/mem/hugetlb/hugemmap/hugemmap08.c
> b/testcases/kernel/mem/hugetlb/hugemmap/hugemmap08.c
> new file mode 100644
> index 000000000..61db030d5
> --- /dev/null
> +++ b/testcases/kernel/mem/hugetlb/hugemmap/hugemmap08.c
> @@ -0,0 +1,144 @@
> +// SPDX-License-Identifier: LGPL-2.1-or-later
> +/*
> + * Copyright (C) 2005-2006 David Gibson & Adam Litke, IBM Corporation.
> + * Author: David Gibson & Adam Litke
> + */
> +
> +/*\
> + * [Description]
> + *
> + * Chunk Overcommit:
> + * 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
> + *
> + */
> +
> +#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 PROC_OVERCOMMIT "/proc/sys/vm/nr_overcommit_hugepages"
> +#define WITH_OVERCOMMIT 0
> +#define WITHOUT_OVERCOMMIT 1
> +
> +static long hpage_size;
> +
> +static void test_chunk_overcommit(void)
> +{
> + unsigned long totpages, chunk1, chunk2;
> + void *p, *q;
> + pid_t child;
> + int status;
> +
> + totpages = SAFE_READ_MEMINFO("HugePages_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,
> + tst_hugetlb_fd, 0);
> +
> + q = mmap(NULL, chunk2*hpage_size, PROT_READ|PROT_WRITE, MAP_SHARED,
> + tst_hugetlb_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(tst_hugetlb_fd, 0);
> +}
> +
> +static void run_test(unsigned int test_type)
> +{
> + unsigned long saved_oc_hugepages;
> +
> + SAFE_FILE_SCANF(PROC_OVERCOMMIT, "%ld", &saved_oc_hugepages);
>

There is unnecessary to read PROC_OVERCOMMIT value again,
we already save/restore it in struct tst_path_val[], so here we
can set it directly to what we expected no matter if the original is 0 or 2.

static void run_test(unsigned int test_type)
{
switch (test_type) {
case WITHOUT_OVERCOMMIT:
tst_res(TINFO, "Without overcommit testing...");
SAFE_FILE_PRINTF(PROC_OVERCOMMIT, "%d", 0);
break;
case WITH_OVERCOMMIT:
tst_res(TINFO, "With overcommit testing...");
SAFE_FILE_PRINTF(PROC_OVERCOMMIT, "%d", 2);
break;
}
test_chunk_overcommit();
}

> + switch (test_type) {
> + case WITHOUT_OVERCOMMIT:
> + tst_res(TINFO, "Without overcommit testing...");
> + if (saved_oc_hugepages > 0)
> + SAFE_FILE_PRINTF(PROC_OVERCOMMIT, "%d", 0);
> + break;
> + case WITH_OVERCOMMIT:
> + tst_res(TINFO, "With overcommit testing...");
> + if (saved_oc_hugepages == 0)
> + SAFE_FILE_PRINTF(PROC_OVERCOMMIT, "%d", 2);
> + break;
> + }
> + test_chunk_overcommit();
> +}
> +
> +static void setup(void)
> +{
> + hpage_size = SAFE_READ_MEMINFO("Hugepagesize:")*1024;
> +}
> +
> +static struct tst_test test = {
> + .needs_root = 1,
> + .needs_hugetlbfs = 1,
> + .needs_unlinked_hugetlb_file = 1,
> + .forks_child = 1,
> + .save_restore = (const struct tst_path_val[]) {
> + {PROC_OVERCOMMIT, NULL},
> + {}
> + },
> + .tcnt = 2,
> + .setup = setup,
> + .test = run_test,
> + .hugepages = {3, TST_NEEDS},
> +};
> +
> --
> 2.31.1
>
>
> --
> Mailing list info: https://lists.linux.it/listinfo/ltp
>
>

--
Regards,
Li Wang

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