On Sat, Jan 18, 2025 at 12:17 PM Darrick J. Wong <djwong@xxxxxxxxxx> wrote:
>
> On Fri, Jan 17, 2025 at 04:47:58PM -0800, Joanne Koong wrote:
> > Add support for reads/writes from buffers backed by hugepages.
> > This can be enabled through the '-h' flag. This flag should only be used
> > on systems where THP capabilities are enabled.
> >
> > This is motivated by a recent bug that was due to faulty handling of
> > userspace buffers backed by hugepages. This patch is a mitigation
> > against problems like this in the future.
> >
> > Signed-off-by: Joanne Koong <joannelkoong@xxxxxxxxx>
> > Reviewed-by: Brian Foster <bfoster@xxxxxxxxxx>
> > ---
> > ltp/fsx.c | 165 +++++++++++++++++++++++++++++++++++++++++++++++++-----
> > 1 file changed, 152 insertions(+), 13 deletions(-)
> >
> > diff --git a/ltp/fsx.c b/ltp/fsx.c
> > index 41933354..1513755f 100644
> > --- a/ltp/fsx.c
> > +++ b/ltp/fsx.c
> > @@ -2833,11 +2846,40 @@ __test_fallocate(int mode, const char *mode_str)
> > #endif
> > }
> >
> > +/*
> > + * Reclaim may break up hugepages, so do a best-effort collapse every once in
> > + * a while.
> > + */
> > +static void
> > +collapse_hugepages(void)
> > +{
> > +#ifdef MADV_COLLAPSE
> > + int interval = 1 << 14; /* 16k */
> > + int ret;
> > +
> > + if (numops && (numops & (interval - 1)) == 0) {
>
> I wonder if this could be collapsed to:
>
> /* re-collapse every 16k fsxops after we start */
> if (!numops || (numops & ((1U << 14) - 1)))
> return;
>
> ret = madvise(...);
>
> But my guess is that the compiler is smart enough to realize that
> interval never changes and fold it into the test expression?
>
> <shrug> Not that passionate either way. :)
Sounds good, I will change it to this and fix the indentation below for v5.
Thanks,
Joanne
>
> > + ret = madvise(hugepages_info.orig_good_buf,
> > + hugepages_info.good_buf_size, MADV_COLLAPSE);
> > + if (ret)
> > + prt("collapsing hugepages for good_buf failed (numops=%llu): %s\n",
> > + numops, strerror(errno));
> > + ret = madvise(hugepages_info.orig_temp_buf,
> > + hugepages_info.temp_buf_size, MADV_COLLAPSE);
> > + if (ret)
> > + prt("collapsing hugepages for temp_buf failed (numops=%llu): %s\n",
> > + numops, strerror(errno));
> > + }
> > +#endif
> > +}
> > +
> > bool
> > keep_running(void)
> > {
> > int ret;
> >
> > + if (hugepages)
> > + collapse_hugepages();
> > +
> > if (deadline.tv_nsec) {
> > struct timespec now;
> >
> > @@ -2856,6 +2898,103 @@ keep_running(void)
> > return numops-- != 0;
> > }
> >
> > +static long
> > +get_hugepage_size(void)
> > +{
> > + const char str[] = "Hugepagesize:";
> > + size_t str_len = sizeof(str) - 1;
> > + unsigned int hugepage_size = 0;
> > + char buffer[64];
> > + FILE *file;
> > +
> > + file = fopen("/proc/meminfo", "r");
> > + if (!file) {
> > + prterr("get_hugepage_size: fopen /proc/meminfo");
> > + return -1;
> > + }
> > + while (fgets(buffer, sizeof(buffer), file)) {
> > + if (strncmp(buffer, str, str_len) == 0) {
> > + sscanf(buffer + str_len, "%u", &hugepage_size);
> > + break;
> > + }
> > + }
> > + fclose(file);
> > + if (!hugepage_size) {
> > + prterr("get_hugepage_size: failed to find "
> > + "hugepage size in /proc/meminfo\n");
> > + return -1;
> > + }
> > +
> > + /* convert from KiB to bytes */
> > + return hugepage_size << 10;
> > +}
> > +
> > +static void *
> > +init_hugepages_buf(unsigned len, int hugepage_size, int alignment, long *buf_size)
> > +{
> > + void *buf = NULL;
> > +#ifdef MADV_COLLAPSE
> > + int ret;
> > + long size = roundup(len, hugepage_size) + alignment;
> > +
> > + ret = posix_memalign(&buf, hugepage_size, size);
> > + if (ret) {
> > + prterr("posix_memalign for buf");
> > + return NULL;
> > + }
> > + memset(buf, '\0', size);
> > + ret = madvise(buf, size, MADV_COLLAPSE);
> > + if (ret) {
> > + prterr("madvise collapse for buf");
> > + free(buf);
> > + return NULL;
> > + }
> > +
> > + *buf_size = size;
> > +#endif
> > + return buf;
> > +}
> > +
> > +static void
> > +init_buffers(void)
> > +{
> > + int i;
> > +
> > + original_buf = (char *) malloc(maxfilelen);
> > + for (i = 0; i < maxfilelen; i++)
> > + original_buf[i] = random() % 256;
> > + if (hugepages) {
> > + long hugepage_size = get_hugepage_size();
> > + if (hugepage_size == -1) {
> > + prterr("get_hugepage_size()");
> > + exit(102);
> > + }
> > + good_buf = init_hugepages_buf(maxfilelen, hugepage_size, writebdy,
> > + &hugepages_info.good_buf_size);
> > + if (!good_buf) {
> > + prterr("init_hugepages_buf failed for good_buf");
> > + exit(103);
> > + }
> > + hugepages_info.orig_good_buf = good_buf;
> > +
> > + temp_buf = init_hugepages_buf(maxoplen, hugepage_size, readbdy,
> > + &hugepages_info.temp_buf_size);
> > + if (!temp_buf) {
> > + prterr("init_hugepages_buf failed for temp_buf");
> > + exit(103);
> > + }
> > + hugepages_info.orig_temp_buf = temp_buf;
> > + } else {
> > + unsigned long good_buf_len = maxfilelen + writebdy;
> > + unsigned long temp_buf_len = maxoplen + readbdy;
> > +
> > + good_buf = calloc(1, good_buf_len);
> > + temp_buf = calloc(1, temp_buf_len);
> > + }
> > + good_buf = round_ptr_up(good_buf, writebdy, 0);
> > + temp_buf = round_ptr_up(temp_buf, readbdy, 0);
> > +}
> > +
> > static struct option longopts[] = {
> > {"replay-ops", required_argument, 0, 256},
> > {"record-ops", optional_argument, 0, 255},
> > @@ -2883,7 +3022,7 @@ main(int argc, char **argv)
> > setvbuf(stdout, (char *)0, _IOLBF, 0); /* line buffered stdout */
> >
> > while ((ch = getopt_long(argc, argv,
> > - "0b:c:de:fg:i:j:kl:m:no:p:qr:s:t:uw:xyABD:EFJKHzCILN:OP:RS:UWXZ",
> > + "0b:c:de:fg:hi:j:kl:m:no:p:qr:s:t:uw:xyABD:EFJKHzCILN:OP:RS:UWXZ",
> > longopts, NULL)) != EOF)
> > switch (ch) {
> > case 'b':
> > @@ -2916,6 +3055,14 @@ main(int argc, char **argv)
> > case 'g':
> > filldata = *optarg;
> > break;
> > + case 'h':
> > +#ifndef MADV_COLLAPSE
> > + fprintf(stderr, "MADV_COLLAPSE not supported. "
> > + "Can't support -h\n");
> > + exit(86);
>
> Excessive indenting here.
>
> With those fixed up,
> Reviewed-by: "Darrick J. Wong" <djwong@xxxxxxxxxx>
>
> --D
>
> > +#endif
> > + hugepages = 1;
> > + break;
> > case 'i':
> > integrity = 1;
> > logdev = strdup(optarg);
> > @@ -3229,15 +3376,7 @@ main(int argc, char **argv)
> > exit(95);
> > }
> > }
> > - original_buf = (char *) malloc(maxfilelen);
> > - for (i = 0; i < maxfilelen; i++)
> > - original_buf[i] = random() % 256;
> > - good_buf = (char *) malloc(maxfilelen + writebdy);
> > - good_buf = round_ptr_up(good_buf, writebdy, 0);
> > - memset(good_buf, '\0', maxfilelen);
> > - temp_buf = (char *) malloc(maxoplen + readbdy);
> > - temp_buf = round_ptr_up(temp_buf, readbdy, 0);
> > - memset(temp_buf, '\0', maxoplen);
> > + init_buffers();
> > if (lite) { /* zero entire existing file */
> > ssize_t written;
> >
> > --
> > 2.47.1
> >
> >
