Re: [PATCH v2 1/2] tools/vm/page_owner_sort.c: Sort by stacktrace before culling

Re: [PATCH v2 1/2] tools/vm/page_owner_sort.c: Sort by stacktrace before culling

[weizhenliang]

On 2021/11/25 3:37, Sean Anderson <seanga2@gmail.com> wrote:

> static int compare_num(const void *p1, const void *p2) @@ -121,6 
>+122,7 @@ static void add_list(char *buf, int len)  
>list[list_size].page_num = get_page_num(buf);  
>memcpy(list[list_size].txt, buf, len);  list[list_size].txt[len] = 0;
>+ list[list_size].stacktrace = strchr(list[list_size].txt, '\n');

When read_block gets an empty line, buf is "\n", then the stacktrace is NULL

> list_size++;
> if (list_size % 1000 == 0) {
> printf("loaded %d\r", list_size);
>@@ -199,7 +201,7 @@ int main(int argc, char **argv)
> 
> printf("sorting ....\n");
> 
>- qsort(list, list_size, sizeof(list[0]), compare_txt);
>+ qsort(list, list_size, sizeof(list[0]), compare_stacktrace);
> 
> list2 = malloc(sizeof(*list) * list_size);  if (!list2) { @@ -211,7 
>+213,7 @@ int main(int argc, char **argv)
> 
> for (i = count = 0; i < list_size; i++) {  if (count == 0 ||
>- strcmp(list2[count-1].txt, list[i].txt) != 0) {
>+ strcmp(list2[count-1].stacktrace, list[i].stacktrace) != 0) {

And when stacktrace is NULL, a segmentation fault will be triggered here.

> list2[count++] = list[i];
> } else {
> list2[count-1].num += list[i].num;

1. Maybe you can check whether the ret of read_block is 0 before add_list,
or whether the len of buf is 0 in add_list
2. Is it necessary to check stacktrace==NULL before use ?

Wei.

Re: [PATCH v2 1/2] tools/vm/page_owner_sort.c: Sort by stacktrace before culling

[Sean Anderson]

On 11/25/21 4:46 AM, weizhenliang wrote:
> On 2021/11/25 3:37, Sean Anderson <seanga2@gmail.com> wrote:
> 
>> static int compare_num(const void *p1, const void *p2) @@ -121,6
>> +122,7 @@ static void add_list(char *buf, int len)
>> list[list_size].page_num = get_page_num(buf);
>> memcpy(list[list_size].txt, buf, len);  list[list_size].txt[len] = 0;
>> + list[list_size].stacktrace = strchr(list[list_size].txt, '\n');
> 
> When read_block gets an empty line, buf is "\n", then the stacktrace is NULL
> 
>> list_size++;
>> if (list_size % 1000 == 0) {
>> printf("loaded %d\r", list_size);
>> @@ -199,7 +201,7 @@ int main(int argc, char **argv)
>>
>> printf("sorting ....\n");
>>
>> - qsort(list, list_size, sizeof(list[0]), compare_txt);
>> + qsort(list, list_size, sizeof(list[0]), compare_stacktrace);
>>
>> list2 = malloc(sizeof(*list) * list_size);  if (!list2) { @@ -211,7
>> +213,7 @@ int main(int argc, char **argv)
>>
>> for (i = count = 0; i < list_size; i++) {  if (count == 0 ||
>> - strcmp(list2[count-1].txt, list[i].txt) != 0) {
>> + strcmp(list2[count-1].stacktrace, list[i].stacktrace) != 0) {
> 
> And when stacktrace is NULL, a segmentation fault will be triggered here.

Ah, whoops. Looks like I check for this in compare_stacktrace but not here.

>> list2[count++] = list[i];
>> } else {
>> list2[count-1].num += list[i].num;
> 
> 1. Maybe you can check whether the ret of read_block is 0 before add_list,
> or whether the len of buf is 0 in add_list

I think this is the best route.

Since this seems to have already been applied I've sent a follow-up patch.

--Sean

[PATCH v2 1/2] tools/vm/page_owner_sort.c: Sort by stacktrace before culling

[Sean Anderson]

The contents of page_owner have changed to include more information than
the stack trace. On a modern kernel, the blocks look like

Page allocated via order 0, mask 0x0(), pid 1, ts 165564237 ns, free_ts 0 ns
 register_early_stack+0x4b/0x90
 init_page_owner+0x39/0x250
 kernel_init_freeable+0x11e/0x242
 kernel_init+0x16/0x130

Sorting by the contents of .txt will result in almost no repeated pages, as
the pid, ts, and free_ts will almost never be the same. Instead, sort by
the contents of the stack trace, which we assume to be whatever is after
the first line.

Signed-off-by: Sean Anderson <seanga2@gmail.com>
---

(no changes since v1)

 tools/vm/page_owner_sort.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/tools/vm/page_owner_sort.c b/tools/vm/page_owner_sort.c
index 9ebb84a9c731..9ad3772a294d 100644
--- a/tools/vm/page_owner_sort.c
+++ b/tools/vm/page_owner_sort.c
@@ -23,6 +23,7 @@
 
 struct block_list {
 	char *txt;
+	char *stacktrace;
 	int len;
 	int num;
 	int page_num;
@@ -51,11 +52,11 @@ int read_block(char *buf, int buf_size, FILE *fin)
 	return -1; /* EOF or no space left in buf. */
 }
 
-static int compare_txt(const void *p1, const void *p2)
+static int compare_stacktrace(const void *p1, const void *p2)
 {
 	const struct block_list *l1 = p1, *l2 = p2;
 
-	return strcmp(l1->txt, l2->txt);
+	return strcmp(l1->stacktrace ?: "", l2->stacktrace ?: "");
 }
 
 static int compare_num(const void *p1, const void *p2)
@@ -121,6 +122,7 @@ static void add_list(char *buf, int len)
 	list[list_size].page_num = get_page_num(buf);
 	memcpy(list[list_size].txt, buf, len);
 	list[list_size].txt[len] = 0;
+	list[list_size].stacktrace = strchr(list[list_size].txt, '\n');
 	list_size++;
 	if (list_size % 1000 == 0) {
 		printf("loaded %d\r", list_size);
@@ -199,7 +201,7 @@ int main(int argc, char **argv)
 
 	printf("sorting ....\n");
 
-	qsort(list, list_size, sizeof(list[0]), compare_txt);
+	qsort(list, list_size, sizeof(list[0]), compare_stacktrace);
 
 	list2 = malloc(sizeof(*list) * list_size);
 	if (!list2) {
@@ -211,7 +213,7 @@ int main(int argc, char **argv)
 
 	for (i = count = 0; i < list_size; i++) {
 		if (count == 0 ||
-		    strcmp(list2[count-1].txt, list[i].txt) != 0) {
+		    strcmp(list2[count-1].stacktrace, list[i].stacktrace) != 0) {
 			list2[count++] = list[i];
 		} else {
 			list2[count-1].num += list[i].num;
-- 
2.33.0