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3a8d2db1c

Denys Vlasenko
Denys Vlasenko
2026-01-20
SUCCESS Duration: 142s

Subject

vmstat: fixes for >4TB memory and long sampling intervals

Binary

No binary (build failed)

Architecture & Compiler Flags

Architecture: x86_64-linux-gnu Compiler: gcc (Ubuntu 11.4.0-1ubuntu1~22.04.3) 11.4.0 
gcc -Wp,-MD,applets/.usage.d -Wall -Wstrict-prototypes -O2 -fomit-frame-pointer      -Iinclude -Iinclude -o applets/usage applets/usage.c

Build Log

(log yok)

Commit Diff GitHub →

procps/vmstat.c +75 -39
procps/vmstat.c+75 -39
@@ -82,9 +82,22 @@ struct col {
#define MOD_DECREMENT 0x04
};
+/* There is no "support huge memory" option, use "large file support" as proxy */
+#if ENABLE_LFS
+typedef unsigned long long data_t;
+# define SPU " %llu"
+# define U "llu"
+#else
+/* this mishandles memory sizes if >4TB of RAM */
+typedef unsigned data_t;
+# define SPU " %u"
+# define U "u"
+#endif
+#define DEBUG_SHOW_5T_MEMFREE 0
+
struct globals {
- unsigned data[NCOLS];
- unsigned prev[NCOLS];
+ data_t data[NCOLS];
+ data_t prev[NCOLS];
};
#define G (*(struct globals*)bb_common_bufsiz1)
#define INIT_G() do { \
@@ -191,16 +204,16 @@ static int find_col(unsigned char from, const char *fromspec)
* Reads current system state into the data array elements corresponding
* to coldescs[] columns.
*/
-static void load_row(unsigned data[NCOLS])
+static void load_row(data_t data[NCOLS])
{
FILE *fp;
char label[32];
char line[256];
int colnum;
- unsigned SwapFree = 0;
- unsigned SwapTotal = 0;
- unsigned Cached = 0;
- unsigned SReclaimable = 0;
+ data_t SwapFree = 0;
+ data_t SwapTotal = 0;
+ data_t Cached = 0;
+ data_t SReclaimable = 0;
memset(data, 0, NCOLS * sizeof(data[0]));
@@ -231,9 +244,9 @@ static void load_row(unsigned data[NCOLS])
STAT_CPU_pseudo_us = 0xd, /* user + nice - pseudo_gu */
_STAT_CPU_max
};
- unsigned num[_STAT_CPU_max];
+ data_t num[_STAT_CPU_max];
int n = sscanf(line,
- "%31s %u %u %u %u %u %u %u %u %u %u",
+ "%31s"SPU SPU SPU SPU SPU SPU SPU SPU SPU SPU,
label,
&num[STAT_CPU_user],
# define _STAT_CPU_first STAT_CPU_user
@@ -277,9 +290,9 @@ static void load_row(unsigned data[NCOLS])
/* FROM_PROC_VMSTAT */
fp = xfopen_for_read("/proc/vmstat");
while (fgets(line, sizeof(line), fp)) {
- unsigned num;
+ data_t num;
- if (sscanf(line, "%31s %u", label, &num) == 2) {
+ if (sscanf(line, "%31s"SPU, label, &num) == 2) {
colnum = find_col(*FROM_PROC_VMSTAT, label);
if (colnum != -1)
data[colnum] = num;
@@ -289,11 +302,13 @@ static void load_row(unsigned data[NCOLS])
/* FROM_PROC_MEMINFO */
fp = xfopen_for_read("/proc/meminfo");
-//FIXME: unsigned is way too narrow (>4TB of RAM machines are not that rare these days)
while (fgets(line, sizeof(line), fp)) {
- unsigned num;
-
- if (sscanf(line, "%31[^:]: %u", label, &num) == 2) {
+ data_t num;
+#if DEBUG_SHOW_5T_MEMFREE
+ if (is_prefixed_with(line, "MemFree:"))
+ strcpy(line, "MemFree: 4444444444 kB\n"); /* overflows 32-bit unsigned */
+#endif
+ if (sscanf(line, "%31[^:]:"SPU, label, &num) == 2) {
/* Store some values for computed (pseudo) values */
if (strcmp(label, "SwapTotal") == 0)
SwapTotal = num;
@@ -330,48 +345,69 @@ static void load_row(unsigned data[NCOLS])
}
/* Modify, format and print a row of data values */
-static void print_row(const unsigned data[NCOLS],
- const unsigned old_data[NCOLS])
+static void print_row(const data_t data[NCOLS],
+ const data_t old_data[NCOLS])
{
const char *coli;
struct col col;
unsigned i;
bool is_first;
- unsigned percent_sum = 0;
int overrun;
+ /* Note: all DELTA counters are truncated to 32 bits here.
+ * Imagine small embedded arch. Kernel does not _need_
+ * to maintain 64-bit cpu stats, they work perfectly fine
+ * when they overflow: userspace is expected to only use diffs anyway.
+ * Therefore we must not assume they are wider than 32 bits
+ * (doing so would cause bugs at the moment a counter overflows).
+ */
+ uint32_t percent_sum = 0;
+ uint32_t delta32[NCOLS];
+ unsigned vshift;
+ vshift = 0;
for (coli = coldescs, i = 0; next_col(&col, &coli); i++) {
- if (col.mod & MOD_PERCENT) {
- unsigned value = data[i];
- if (col.mod & MOD_DELTA) {
- value -= old_data[i];
+ if (col.mod & MOD_DELTA) {
+ uint32_t value = data[i];
+ value -= old_data[i];
//For some counters, kernel does not guarantee that they never go backwards.
-//Either due to bugs, or sometimes it's just too hard to 100.00% guarantee that
+//Either due to bugs, or sometimes it's just too hard to 100.00% guarantee it
//(imagine the horrors of reliably and locklessly collecting per-CPU counters).
//The idea is that _userspace_ can semi-trivially work around rare small backward steps:
- if ((int)value < 0) value = 0;
+ if ((int32_t)value < 0)
+ value = 0;
+ delta32[i] = value;
+ if (col.mod & MOD_PERCENT) {
+ /* Ensure deltas < 2^32 / 128 (0x2000000) and percent_sum can't overflow */
+//If we don't do this, if running "vmstat MANY_SECS", percent_sum is ~MANY_SECS*1000*NUM_CPUS,
+//on 100-cpu machine, at ~400 second-long vmstat periods, counters may be > 0x2000000 here.
+ while ((value >> vshift) >= 0x2000000) {
+ percent_sum >>= 1;
+ vshift++;
+ }
+ percent_sum += (value >> vshift);
}
- percent_sum += value;
}
}
+//debug: reduce 0x2000000 to 0x2000 and try "vmstat 60" or so:
+//bb_error_msg("percent_sum:%u vshift:%u", (unsigned)percent_sum, vshift);
overrun = 0;
is_first = 1;
for (coli = coldescs, i = 0; next_col(&col, &coli); i++) {
- unsigned value = data[i];
-
- if (col.mod & MOD_DELTA) {
- value -= old_data[i];
-//For some counters, kernel does not guarantee that they never go backwards
- if ((int)value < 0) value = 0;
- }
- if (col.mod & MOD_PERCENT) {
- value = percent_sum ? 100 * value / percent_sum : 0;
- if (value >= 100) /* sanity check + show "99" for 100% to not overflow col width */
- value = 99;
+ data_t value = (col.mod & MOD_DELTA) ? delta32[i] : data[i];
+
+ /* the !0 check is needed in MOD_DECREMENT, might as well do it sooner */
+ if (value != 0) {
+ if ((col.mod & MOD_PERCENT) && percent_sum != 0) {
+ value = 100 * ((uint32_t)value >> vshift) / percent_sum;
+ /* narrow 32x32->32 multiply is ok since (value >> vshift) is < 2^32 / 128 */
+ if (value >= 100) /* sanity check + show "99" for 100% to not overflow col width */
+ value = 99;
+ } /* else: if percent_sum = 0, all values are 0 too, no need to calculate % */
+
+ if (col.mod & MOD_DECREMENT)
+ value--;
}
- if ((col.mod & MOD_DECREMENT) && value)
- value--;
if (!is_first)
bb_putchar(' ');
@@ -405,7 +441,7 @@ static void print_row(const unsigned data[NCOLS],
smart_ulltoa5(value, buf45, " kmgtpezy")[0] = '\0';
chars_printed = printf("%*s", width, skip_whitespace(buf45));
} else {
- chars_printed = printf("%*u", width, value);
+ chars_printed = printf("%*"U, width, value);
}
overrun += (chars_printed - col.width);
}