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

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Date:   Thu, 25 Nov 2021 11:26:59 -0500
From:   Sean Anderson <seanga2@...il.com>
To:     weizhenliang <weizhenliang@...wei.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Changhee Han <ch0.han@....com>,
        Tang Bin <tangbin@...s.chinamobile.com>,
        Zhang Shengju <zhangshengju@...s.chinamobile.com>
Subject: Re: [PATCH v2 1/2] tools/vm/page_owner_sort.c: Sort by stacktrace
 before culling

On 11/25/21 4:46 AM, weizhenliang wrote:
> On 2021/11/25 3:37, Sean Anderson <seanga2@...il.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