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[108.18.207.184]) by smtp.googlemail.com with ESMTPSA id g12sm1759780qtk.69.2021.11.25.08.26.59 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 25 Nov 2021 08:27:00 -0800 (PST) Subject: Re: [PATCH v2 1/2] tools/vm/page_owner_sort.c: Sort by stacktrace before culling To: weizhenliang , "linux-kernel@vger.kernel.org" , Andrew Morton Cc: Changhee Han , Tang Bin , Zhang Shengju References: <22bad523dffb4681a201e6fedef7c50d@huawei.com> From: Sean Anderson Message-ID: Date: Thu, 25 Nov 2021 11:26:59 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.12.0 MIME-Version: 1.0 In-Reply-To: <22bad523dffb4681a201e6fedef7c50d@huawei.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/25/21 4:46 AM, weizhenliang wrote: > On 2021/11/25 3:37, Sean Anderson 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