[PATCH] tools/vm/page-types.c: page-cache sniffing feature

From: Konstantin Khlebnikov
Date: Wed Feb 26 2014 - 02:57:37 EST

After this patch 'page-types' can walk on filesystem mappings and analize
populated page cache pages mostly without disturbing its state.

It maps chunk of file, marks VMA as MADV_RANDOM to turn off readahead,
pokes VMA via mincore() to determine cached pages, triggers page-fault
only for them, and finally gathers information via pagemap/kpageflags.
Before unmap it marks VMA as MADV_SEQUENTIAL for ignoring reference bits.

usage: page-types -f <path>

If <path> is directory it will analyse all files in all subdirectories.

Symlinks are not followed as well as mount points. Hardlinks aren't handled,
they'll be dumbed as many times as they are found. Recursive walk brings all
dentries into dcache and populates page cache of block-devices aka 'Buffers'.

Probably it's worth to add ioctl for dumping file page cache as array of PFNs
as a replacement for this hackish juggling with mmap/madvise/mincore/pagemap.
Also recursive walk could be replaced with dumping cached inodes via some ioctl
or debugfs interface followed by openning them via open_by_handle_at, this
would fix hardlinks handling and unneeded population of dcache and buffers.
This interface might be used as data source for constructing readahead plans
and for background optimizations of actively used files.

collateral changes:
+ fix 64-bit LFS: define _FILE_OFFSET_BITS instead of _LARGEFILE64_SOURCE
+ replace lseek + read with single pread
+ make show_page_range() reusable after flush

usage example:

~/src/linux/tools/vm$ sudo ./page-types -L -f page-types
foffset offset flags
page-types Inode: 2229277 Size: 89065 (22 pages)
Modify: Tue Feb 25 12:00:59 2014 (162 seconds ago)
Access: Tue Feb 25 12:01:00 2014 (161 seconds ago)
0 3cbf3b __RU_lA____M________________________
1 38946a __RU_lA____M________________________
2 1a3cec __RU_lA____M________________________
3 1a8321 __RU_lA____M________________________
4 3af7cc __RU_lA____M________________________
5 1ed532 __RU_lA_____________________________
6 2e436a __RU_lA_____________________________
7 29a35e ___U_lA_____________________________
8 2de86e ___U_lA_____________________________
9 3bdfb4 ___U_lA_____________________________
10 3cd8a3 ___U_lA_____________________________
11 2afa50 ___U_lA_____________________________
12 2534c2 ___U_lA_____________________________
13 1b7a40 ___U_lA_____________________________
14 17b0be ___U_lA_____________________________
15 392b0c ___U_lA_____________________________
16 3ba46a __RU_lA_____________________________
17 397dc8 ___U_lA_____________________________
18 1f2a36 ___U_lA_____________________________
19 21fd30 __RU_lA_____________________________
20 2c35ba __RU_l______________________________
21 20f181 __RU_l______________________________


flags page-count MB symbolic-flags long-symbolic-flags
0x000000000000002c 2 0 __RU_l______________________________ referenced,uptodate,lru
0x0000000000000068 11 0 ___U_lA_____________________________ uptodate,lru,active
0x000000000000006c 4 0 __RU_lA_____________________________ referenced,uptodate,lru,active
0x000000000000086c 5 0 __RU_lA____M________________________ referenced,uptodate,lru,active,mmap
total 22 0



~/src/linux/tools/vm$ sudo ./page-types -f /
flags page-count MB symbolic-flags long-symbolic-flags
0x0000000000000028 21761 85 ___U_l______________________________ uptodate,lru
0x000000000000002c 127279 497 __RU_l______________________________ referenced,uptodate,lru
0x0000000000000068 74160 289 ___U_lA_____________________________ uptodate,lru,active
0x000000000000006c 84469 329 __RU_lA_____________________________ referenced,uptodate,lru,active
0x000000000000007c 1 0 __RUDlA_____________________________ referenced,uptodate,dirty,lru,active
0x0000000000000228 370 1 ___U_l___I__________________________ uptodate,lru,reclaim
0x0000000000000828 49 0 ___U_l_____M________________________ uptodate,lru,mmap
0x000000000000082c 126 0 __RU_l_____M________________________ referenced,uptodate,lru,mmap
0x0000000000000868 137 0 ___U_lA____M________________________ uptodate,lru,active,mmap
0x000000000000086c 12890 50 __RU_lA____M________________________ referenced,uptodate,lru,active,mmap
total 321242 1254

Signed-off-by: Konstantin Khlebnikov <koct9i@xxxxxxxxx>
---
tools/vm/page-types.c | 170 ++++++++++++++++++++++++++++++++++++++++++++-----
1 file changed, 152 insertions(+), 18 deletions(-)

diff --git a/tools/vm/page-types.c b/tools/vm/page-types.c
index f9be24d..05654f5 100644
--- a/tools/vm/page-types.c
+++ b/tools/vm/page-types.c
@@ -19,7 +19,8 @@
* Authors: Wu Fengguang <fengguang.wu@xxxxxxxxx>
*/

-#define _LARGEFILE64_SOURCE
+#define _FILE_OFFSET_BITS 64
+#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
@@ -29,11 +30,14 @@
#include <getopt.h>
#include <limits.h>
#include <assert.h>
+#include <ftw.h>
+#include <time.h>
#include <sys/types.h>
#include <sys/errno.h>
#include <sys/fcntl.h>
#include <sys/mount.h>
#include <sys/statfs.h>
+#include <sys/mman.h>
#include "../../include/uapi/linux/magic.h"
#include "../../include/uapi/linux/kernel-page-flags.h"
#include <api/fs/debugfs.h>
@@ -158,6 +162,7 @@ static int opt_raw; /* for kernel developers */
static int opt_list; /* list pages (in ranges) */
static int opt_no_summary; /* don't show summary */
static pid_t opt_pid; /* process to walk */
+const char * opt_file;

#define MAX_ADDR_RANGES 1024
static int nr_addr_ranges;
@@ -253,12 +258,7 @@ static unsigned long do_u64_read(int fd, char *name,
if (index > ULONG_MAX / 8)
fatal("index overflow: %lu\n", index);

- if (lseek(fd, index * 8, SEEK_SET) < 0) {
- perror(name);
- exit(EXIT_FAILURE);
- }
-
- bytes = read(fd, buf, count * 8);
+ bytes = pread(fd, buf, count * 8, (off_t)index * 8);
if (bytes < 0) {
perror(name);
exit(EXIT_FAILURE);
@@ -343,8 +343,8 @@ static char *page_flag_longname(uint64_t flags)
* page list and summary
*/

-static void show_page_range(unsigned long voffset,
- unsigned long offset, uint64_t flags)
+static void show_page_range(unsigned long voffset, unsigned long offset,
+ unsigned long size, uint64_t flags)
{
static uint64_t flags0;
static unsigned long voff;
@@ -352,14 +352,16 @@ static void show_page_range(unsigned long voffset,
static unsigned long count;

if (flags == flags0 && offset == index + count &&
- (!opt_pid || voffset == voff + count)) {
- count++;
+ size && voffset == voff + count) {
+ count += size;
return;
}

if (count) {
if (opt_pid)
printf("%lx\t", voff);
+ if (opt_file)
+ printf("%lu\t", voff);
printf("%lx\t%lx\t%s\n",
index, count, page_flag_name(flags0));
}
@@ -367,7 +369,12 @@ static void show_page_range(unsigned long voffset,
flags0 = flags;
index = offset;
voff = voffset;
- count = 1;
+ count = size;
+}
+
+static void flush_page_range(void)
+{
+ show_page_range(0, 0, 0, 0);
}

static void show_page(unsigned long voffset,
@@ -375,6 +382,8 @@ static void show_page(unsigned long voffset,
{
if (opt_pid)
printf("%lx\t", voffset);
+ if (opt_file)
+ printf("%lu\t", voffset);
printf("%lx\t%s\n", offset, page_flag_name(flags));
}

@@ -565,7 +574,7 @@ static void add_page(unsigned long voffset,
unpoison_page(offset);

if (opt_list == 1)
- show_page_range(voffset, offset, flags);
+ show_page_range(voffset, offset, 1, flags);
else if (opt_list == 2)
show_page(voffset, offset, flags);

@@ -667,7 +676,7 @@ static void walk_addr_ranges(void)

for (i = 0; i < nr_addr_ranges; i++)
if (!opt_pid)
- walk_pfn(0, opt_offset[i], opt_size[i], 0);
+ walk_pfn(opt_offset[i], opt_offset[i], opt_size[i], 0);
else
walk_task(opt_offset[i], opt_size[i]);

@@ -699,9 +708,7 @@ static void usage(void)
" -a|--addr addr-spec Walk a range of pages\n"
" -b|--bits bits-spec Walk pages with specified bits\n"
" -p|--pid pid Walk process address space\n"
-#if 0 /* planned features */
" -f|--file filename Walk file address space\n"
-#endif
" -l|--list Show page details in ranges\n"
" -L|--list-each Show page details one by one\n"
" -N|--no-summary Don't show summary info\n"
@@ -799,8 +806,130 @@ static void parse_pid(const char *str)
fclose(file);
}

+static void show_file(const char *name, const struct stat *st)
+{
+ unsigned long long size = st->st_size;
+ char atime[64], mtime[64];
+ long now = time(NULL);
+
+ printf("%s\tInode: %u\tSize: %llu (%llu pages)\n",
+ name, (unsigned)st->st_ino,
+ size, (size + page_size - 1) / page_size);
+
+ strftime(atime, sizeof(atime), "%c", localtime(&st->st_atime));
+ strftime(mtime, sizeof(mtime), "%c", localtime(&st->st_mtime));
+
+ printf("Modify: %s (%ld seconds ago)\nAccess: %s (%ld seconds ago)\n",
+ mtime, now - st->st_mtime,
+ atime, now - st->st_atime);
+}
+
+static void walk_file(const char *name, const struct stat *st)
+{
+ uint8_t vec[PAGEMAP_BATCH];
+ uint64_t buf[PAGEMAP_BATCH], flags;
+ unsigned long nr_pages, pfn, i;
+ int fd;
+ off_t off;
+ ssize_t len;
+ void *ptr;
+ int first = 1;
+
+ fd = checked_open(name, O_RDONLY|O_NOATIME|O_NOFOLLOW);
+
+ for (off = 0; off < st->st_size; off += len) {
+ nr_pages = (st->st_size - off + page_size - 1) / page_size;
+ if (nr_pages > PAGEMAP_BATCH)
+ nr_pages = PAGEMAP_BATCH;
+ len = nr_pages * page_size;
+
+ ptr = mmap(NULL, len, PROT_READ, MAP_SHARED, fd, off);
+ if (ptr == MAP_FAILED)
+ fatal("mmap failed: %s", name);
+
+ /* determine cached pages */
+ if (mincore(ptr, len, vec))
+ fatal("mincore failed: %s", name);
+
+ /* turn off readahead */
+ if (madvise(ptr, len, MADV_RANDOM))
+ fatal("madvice failed: %s", name);
+
+ /* populate ptes */
+ for (i = 0; i < nr_pages ; i++) {
+ if (vec[i] & 1)
+ (void)*(volatile int *)(ptr + i * page_size);
+ }
+
+ /* turn off harvesting reference bits */
+ if (madvise(ptr, len, MADV_SEQUENTIAL))
+ fatal("madvice failed: %s", name);
+
+ if (pagemap_read(buf, (unsigned long)ptr / page_size,
+ nr_pages) != nr_pages)
+ fatal("cannot read pagemap");
+
+ munmap(ptr, len);
+
+ for (i = 0; i < nr_pages; i++) {
+ pfn = pagemap_pfn(buf[i]);
+ if (!pfn)
+ continue;
+ if (!kpageflags_read(&flags, pfn, 1))
+ continue;
+ if (first && opt_list) {
+ first = 0;
+ flush_page_range();
+ show_file(name, st);
+ }
+ add_page(off / page_size + i, pfn, flags, buf[i]);
+ }
+ }
+
+ close(fd);
+}
+
+int walk_tree(const char *name, const struct stat *st, int type, struct FTW *f)
+{
+ (void)f;
+ switch (type) {
+ case FTW_F:
+ if (S_ISREG(st->st_mode))
+ walk_file(name, st);
+ break;
+ case FTW_DNR:
+ fprintf(stderr, "cannot read dir: %s\n", name);
+ break;
+ }
+ return 0;
+}
+
+static void walk_page_cache(void)
+{
+ struct stat st;
+
+ kpageflags_fd = checked_open(PROC_KPAGEFLAGS, O_RDONLY);
+ pagemap_fd = checked_open("/proc/self/pagemap", O_RDONLY);
+
+ if (stat(opt_file, &st))
+ fatal("stat failed: %s\n", opt_file);
+
+ if (S_ISREG(st.st_mode)) {
+ walk_file(opt_file, &st);
+ } else if (S_ISDIR(st.st_mode)) {
+ /* do not follow symlinks and mountpoints */
+ if (nftw(opt_file, walk_tree, 64, FTW_MOUNT | FTW_PHYS) < 0)
+ fatal("nftw failed: %s\n", opt_file);
+ } else
+ fatal("unhandled file type: %s\n", opt_file);
+
+ close(kpageflags_fd);
+ close(pagemap_fd);
+}
+
static void parse_file(const char *name)
{
+ opt_file = name;
}

static void parse_addr_range(const char *optarg)
@@ -991,15 +1120,20 @@ int main(int argc, char *argv[])

if (opt_list && opt_pid)
printf("voffset\t");
+ if (opt_list && opt_file)
+ printf("foffset\t");
if (opt_list == 1)
printf("offset\tlen\tflags\n");
if (opt_list == 2)
printf("offset\tflags\n");

- walk_addr_ranges();
+ if (opt_file)
+ walk_page_cache();
+ else
+ walk_addr_ranges();

if (opt_list == 1)
- show_page_range(0, 0, 0); /* drain the buffer */
+ flush_page_range();

if (opt_no_summary)
return 0;

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/