page-types: decode flags directly from command line

Teach page-types to decode page flags directly from the command line.

Why is this useful? For instance, if you're using memory hotplug and see this in /var/log/messages:

	kernel: removing from LRU failed 3836dd0/1/1e00000000000400

It would be nice to decode those page flags without staring at the source.

Example usage and output:

linux-2.6/Documentation/vm$ ./page-types -d 0x1e00000000000400
flags page-count MB symbolic-flags long-symbolic-flags

0x1e00000000000400	         1        0  __________B_______________________buddy
             total	         1        0

Signed-off-by Alex Chiang <[email protected]>

---
 page-types.c |   26 ++++++++++++++++++++++++--
 1 file changed, 24 insertions(+), 2 deletions(-)

---

Documentation/vm/page-types.c +24 -2

index 3ec4f2a..a55c624 100644
@@ -674,6 +674,7 @@ static void usage(void)
 	printf(
 "page-types [options]\n"
 "            -r|--raw                  Raw mode, for kernel developers\n"
+"            -d|--decode  flags        Decode a single page's flags\n"
 "            -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"

@@ -682,10 +683,12 @@ static void usage(void)
 #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 summay info\n"
+"            -N|--no-summary           Don't show summary info\n"
 "            -X|--hwpoison             hwpoison pages\n"
 "            -x|--unpoison             unpoison pages\n"
 "            -h|--help                 Show this usage message\n"
+"flags:\n"
+"            0x0000000000000400        A single page's flags, e.g.\n"
 "addr-spec:\n"
 "            N                         one page at offset N (unit: pages)\n"
 "            N+M                       pages range from N to N+M-1\n"

@@ -884,12 +887,28 @@ static void parse_bits_mask(const char *optarg)
 	add_bits_filter(mask, bits);
 }
 
+static void decode_flags_and_exit(const char *optarg)
+{
+	uint64_t flags;
+
+	flags = parse_number(optarg);
+
+	opt_list = 0;
+	opt_hwpoison = 0;
+	opt_unpoison = 0;
+
+	add_page(0, 0, flags);
+	show_summary();
+
+	exit(0);
+}
 
 static struct option opts[] = {
 	{ "raw"       , 0, NULL, 'r' },
 	{ "pid"       , 1, NULL, 'p' },
 	{ "file"      , 1, NULL, 'f' },
 	{ "addr"      , 1, NULL, 'a' },
+	{ "decode"    , 1, NULL, 'd' },
 	{ "bits"      , 1, NULL, 'b' },
 	{ "list"      , 0, NULL, 'l' },
 	{ "list-each" , 0, NULL, 'L' },

@@ -907,7 +926,7 @@ int main(int argc, char *argv[])
 	page_size = getpagesize();
 
 	while ((c = getopt_long(argc, argv,
-				"rp:f:a:b:lLNXxh", opts, NULL)) != -1) {
+				"rp:f:a:b:d:lLNXxh", opts, NULL)) != -1) {
 		switch (c) {
 		case 'r':
 			opt_raw = 1;

@@ -924,6 +943,9 @@ int main(int argc, char *argv[])
 		case 'b':
 			parse_bits_mask(optarg);
 			break;
+		case 'd':
+			decode_flags_and_exit(optarg);
+			break;
 		case 'l':
 			opt_list = 1;
 			break;

Quoted 7 lines

Why is this useful? For instance, if you're using memory hotplug and see this in /var/log/messages:

	kernel: removing from LRU failed 3836dd0/1/1e00000000000400

It would be nice to decode those page flags without staring at the source.

In fact it's more than decode - encoding is also possible with the _same_ code! So maybe "-d" and help message will not be all that appropriate.

Quoted 6 lines

Example usage and output:

linux-2.6/Documentation/vm$ ./page-types -d 0x1e00000000000400
flags page-count MB symbolic-flags long-symbolic-flags

0x1e00000000000400	         1        0  __________B_______________________buddy
             total	         1        0

The output is a bit redundant - so does the code. Could you simplify them a bit?

Hi Fengguang,

* Wu Fengguang <[email protected]>:

Quoted 12 lines · Alex Chiang

Quoted 7 lines

Why is this useful? For instance, if you're using memory hotplug and see this in /var/log/messages:

	kernel: removing from LRU failed 3836dd0/1/1e00000000000400

It would be nice to decode those page flags without staring at the source.

In fact it's more than decode - encoding is also possible with the _same_ code! So maybe "-d" and help message will not be all that appropriate.

I'm sorry, I don't understand this use case, so I'm not sure what you're asking me to do.

You're saying that a use case would be something like:

	./page-types --encode referenced,mmap
	0x0000000000000004

?

If that's what you're asking for, I guess I'm not sure why that's so useful, but then again, I'm a vm n00b so there are probably lots of things I don't understand. ;)

Quoted 9 lines

Quoted 6 lines

Example usage and output:

linux-2.6/Documentation/vm$ ./page-types -d 0x1e00000000000400
flags page-count MB symbolic-flags long-symbolic-flags

0x1e00000000000400	         1        0  __________B_______________________buddy
             total	         1        0

The output is a bit redundant - so does the code. Could you simplify them a bit?

Well, the code is redundant, but add_page() / show_summary() is a simple sequence.

In contrast, I think I'd have to modify walk_addr_ranges() and maybe walk_pfn() to do something special when we don't really want to do any address space walking, and simply want to decode/encode some user input.

Maybe I don't understand you fully? Could you give me a better idea of what you're looking for?

As for the output, I'm just reusing show_summary(). Maybe we don't need the flags, page-count, and MB columns, but again, the patch would be more intrusisive because we'd have to teach show_summary() about the special case.

Anyway, I'm happy to make changes closer to what you're looking for, but I'd like some more guidance as to what you're expecting.

Thanks,
/ac