Re: [Bug 12832] New: kernel leaks a lot of memory

[Wu Fengguang <fengguang.wu@intel.com>]

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On Tue, Mar 10, 2009 at 10:21:18PM +0200, Pierre Ossman wrote:
> On Tue, 10 Mar 2009 21:11:55 +0800
> Wu Fengguang <fengguang.wu@intel.com> wrote:
>
> > If we run eatmem or the following commands to take up free memory,
> > the missing pages will show up :-)
> >
> >         dd if=/dev/zero of=/tmp/s bs=1M count=1 seek=1024
> >         cp /tmp/s /dev/null
> >
>
> Not here, which now means I've "found" all of my missing 170 MB.
>
> On 2.6.27, when I fill the page cache I still get over 90 MB left in
> "noflags":
>
> 0x20000	     24394       95  _________________n  noflags
>
> The same thing with 2.6.26 almost completely drains it:
>
> 0x20000	      3697       14  _________________n  noflags
>
> Another interesting data point is that those 80 MB always seem to be
> the exact same number of pages every boot.

This 80MB noflags pages together with the below 80MB lru pages are
very close to the missing page numbers :-) Could you run the following
commands on fresh booted 2.6.27 and post the output files? Thank you!

        dd if=/dev/zero of=/tmp/s bs=1M count=1 seek=1024
        cp /tmp/s /dev/null

        ./page-flags > flags
        ./page-areas =0x20000 > areas-noflags
        ./page-areas =0x00020 > areas-lru

The attached page-areas.c can do the above exact flags matching.

> After that, a comparison shows that this row is in 2.6.27, but not
> 2.6.26:
>
> 0x00020      20576       80  _____l____________  lru
>
> Unfortunately there are about 170 MB of missing memory, not 80. So we
> probably need to dig deeper. But does the above say anything to you?

> I had to remove PG_swapbacked and PG_private2 as 2.6.26/2.6.27 didn't
> have those bits.

Ah sorry! I forgot to switch the tree back to 2.6.27 to run a test.

Thanks,
Fengguang


[-- Attachment #2: page-areas.c --]
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#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <stdint.h>
#include <sys/types.h>
#include <sys/errno.h>
#include <sys/fcntl.h>

/* copied from kpageflags_read() */
enum {
	KPF_LOCKED,	/*  0 */
	KPF_ERROR,	/*  1 */
	KPF_REFERENCED,	/*  2 */
	KPF_UPTODATE,	/*  3 */
	KPF_DIRTY,	/*  4 */
	KPF_LRU,	/*  5 */
	KPF_ACTIVE,	/*  6 */
	KPF_SLAB,	/*  7 */
	KPF_WRITEBACK,	/*  8 */
	KPF_RECLAIM,	/*  9 */
	KPF_BUDDY,	/* 10 */
	KPF_RESERVED,	/* 11 */
	KPF_SWAPCACHE,	/* 12 */
	KPF_SWAPBACKED,	/* 13 */
        KPF_PRIVATE,    /* 14 */
        KPF_PRIVATE2,   /* 15 */
        KPF_NOPAGE,     /* 16 */
        KPF_NOFLAGS,    /* 17 */
	KPF_NUM
};
#define KPF_BYTES	8

#define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))

static char *page_flag_names[] = {
	[KPF_LOCKED]		= "L:locked",
	[KPF_ERROR]		= "E:error",
	[KPF_REFERENCED]	= "R:referenced",
	[KPF_UPTODATE]		= "U:uptodate",
	[KPF_DIRTY]		= "D:dirty",
	[KPF_LRU]		= "l:lru",
	[KPF_ACTIVE]		= "A:active",
	[KPF_SLAB]		= "S:slab",
	[KPF_WRITEBACK]		= "W:writeback",
	[KPF_RECLAIM]		= "x:reclaim",
	[KPF_BUDDY]		= "B:buddy",
	[KPF_RESERVED]		= "r:reserved",
	[KPF_SWAPBACKED]	= "b:swapbacked",
	[KPF_SWAPCACHE]		= "c:swapcache",
	[KPF_PRIVATE]		= "P:private",
	[KPF_PRIVATE2]		= "p:private_2",
	[KPF_NOPAGE]		= "N:nopage",
	[KPF_NOFLAGS]		= "n:noflags",
};

static unsigned long page_count[(1 << KPF_NUM)];
static unsigned long nr_pages;
static uint64_t kpageflags[KPF_BYTES * (8<<20)];

char *page_flag_name(uint64_t flags)
{
	int i;
	static char buf[64];

	for (i = 0; i < ARRAY_SIZE(page_flag_names); i++)
		buf[i] = (flags & (1 << i)) ? page_flag_names[i][0] : '_';

	return buf;
}

char *page_flag_longname(uint64_t flags)
{
	int i, n;
	static char buf[1024];

	for (i = 0, n = 0; i < ARRAY_SIZE(page_flag_names); i++)
		if (flags & (1<<i))
		       n += snprintf(buf + n, sizeof(buf) - n, "%s,",
				       page_flag_names[i] + 2);
	if (n)
		n--;
	buf[n] = '\0';

	return buf;
}

static unsigned long pages2kb(unsigned long pages)
{
	return (pages * getpagesize()) >> 10;
}

static void add_index(unsigned long index)
{
	static unsigned long offset, len;

	if (index == offset + len)
		len++;
	else {
		if (len)
			printf("%10lu %8lu %8luKB\n", offset, len, pages2kb(len));
		offset = index;
		len = 1;
	}
}

static void usage(const char *prog)
{
	printf("Usage: %s page_flags\n", prog);
}

int main(int argc, char *argv[])
{
	static char kpageflags_name[] = "/proc/kpageflags";
	unsigned long match_flags, match_exact;
	unsigned long i;
	char *p;
	int fd;

	if (argc < 2) {
		usage(argv[0]);
		exit(1);
	}

	match_exact = 0;
	p = argv[1];
	if (p[0] == '=') {
		match_exact = 1;
		p++;
	}
	match_flags = strtol(p, 0, 16);

	fd = open(kpageflags_name, O_RDONLY);
	if (fd < 0) {
		perror(kpageflags_name);
		exit(1);
	}

	nr_pages = read(fd, kpageflags, sizeof(kpageflags));
	if (nr_pages <= 0) {
		perror(kpageflags_name);
		exit(2);
	}
	if (nr_pages % KPF_BYTES != 0) {
		fprintf(stderr, "%s: partial read: %lu bytes\n",
				argv[0], nr_pages);
		exit(3);
	}
	nr_pages = nr_pages / KPF_BYTES;

	printf("    offset      len         KB\n");
	for (i = 0; i < nr_pages; i++) {
		if (!match_exact && ((kpageflags[i] & match_flags) == match_flags) ||
		    (match_exact && kpageflags[i] == match_flags))
			add_index(i);
	}
	add_index(0);

	return 0;
}