[fix](cgroup memory) Correct cgroup mem info cache (apache#36966)

## Proposed changes
After upgrading to Doris 2.1.3, we noticed that the "sys available
memory" in be.INFO continuously decreases until it falls below the
warning water mark, leading to persistent garbage collection (GC)
despite the actual memory usage being very low. And The cache in cgroup
mem info is always 0. Consequently, I identified an error in the
calculation of available memory in cgroup memory:

1. The memory information for cgroup memory is stored in the file
"memory.stat" rather than "memory.meminfo" (in fact, the
"memory.meminfo" file does not exist). You can see the files under the
cgroup path in the attached screenshot1.
2. The output content of "memory.stat" is shown in the screenshot1
below.

<img width="1720" alt="image"
src="https://github.com/apache/doris/assets/38196564/e654322e-9bf4-4f5e-951f-99e101ebbf47">
<img width="1364" alt="image"
src="https://github.com/apache/doris/assets/38196564/02cf8899-7618-4d5f-bf59-68fa0c90ebf2">


<!--Describe your changes.-->
My change is about two steps:
1. Modified the file name for mem info in cgroup.
2. Modified the process for extracting the cache from cgroup.

Co-authored-by: Xinyi Zou <[email protected]>

be/src/util/cgroup_util.cpp

@@ -184,7 +184,7 @@ Status CGroupUtil::find_cgroup_mem_info(std::string* file_path) {
     }
     string cgroup_path;
     RETURN_IF_ERROR(find_abs_cgroup_path("memory", &cgroup_path));
-    *file_path = cgroup_path + "/memory.meminfo";
+    *file_path = cgroup_path + "/memory.stat";
     return Status::OK();
 }
 

be/src/util/mem_info.cpp

@@ -423,7 +423,7 @@ void MemInfo::refresh_proc_meminfo() {
                 if (fields.size() < 2) {
                     continue;
                 }
-                std::string key = fields[0].substr(0, fields[0].size() - 1);
+                std::string key = fields[0].substr(0, fields[0].size());
 
                 StringParser::ParseResult result;
                 auto mem_value = StringParser::string_to_int<int64_t>(fields[1].data(),
@@ -449,19 +449,19 @@ void MemInfo::refresh_proc_meminfo() {
             // https://serverfault.com/questions/902009/the-memory-usage-reported-in-cgroup-differs-from-the-free-command
             // memory.usage_in_bytes ~= free.used + free.(buff/cache) - (buff)
             // so, memory.usage_in_bytes - memory.meminfo["Cached"]
-            _s_cgroup_mem_usage = cgroup_mem_usage - _s_cgroup_mem_info_bytes["Cached"];
+            _s_cgroup_mem_usage = cgroup_mem_usage - _s_cgroup_mem_info_bytes["cache"];
             // wait 10s, 100 * 100ms, avoid too frequently.
             _s_cgroup_mem_refresh_wait_times = -100;
             LOG(INFO) << "Refresh cgroup memory win, refresh again after 10s, cgroup mem limit: "
                       << _s_cgroup_mem_limit << ", cgroup mem usage: " << _s_cgroup_mem_usage
-                      << ", cgroup mem info cached: " << _s_cgroup_mem_info_bytes["Cached"];
+                      << ", cgroup mem info cached: " << _s_cgroup_mem_info_bytes["cache"];
         } else {
             // find cgroup failed, wait 300s, 1000 * 100ms.
             _s_cgroup_mem_refresh_wait_times = -3000;
             LOG(INFO)
                     << "Refresh cgroup memory failed, refresh again after 300s, cgroup mem limit: "
                     << _s_cgroup_mem_limit << ", cgroup mem usage: " << _s_cgroup_mem_usage
-                    << ", cgroup mem info cached: " << _s_cgroup_mem_info_bytes["Cached"];
+                    << ", cgroup mem info cached: " << _s_cgroup_mem_info_bytes["cache"];
         }
     } else {
         if (config::enable_use_cgroup_memory_info) {