Mem leak fix when new upstreams are added

[cinquemb]

In order to avoid append to the existing ngx_conf_t pool, this will create a temp ngx_conf_t pool in refresh_upstream, swap old one out and delete if upstreams change.

This also implements some of the changes similar to what https://github.com/GUI/nginx-upstream-dynamic-servers/pull/33/files (no need for exit_procces, using ngx_http_upstream_init_round_robin instead of init), but avoids having to count refs to pools to address the leak.

Still leaks mem, but way less now.

Sample after ~12 hours with 2 upstreams, and about 82 different nginx servers:

$ sudo cat /proc/2048/smaps > AfterMemInc.txt
$ diff -u BeforeMemInc.txt AfterMemInc.txt 
--- BeforeMemInc.txt	2020-09-08 12:13:22.750709681 +0000
+++ AfterMemInc.txt	2020-09-08 23:52:53.499870017 +0000
@@ -94,14 +94,14 @@
 Size:              13984 kB
 KernelPageSize:        4 kB
 MMUPageSize:           4 kB
-Rss:               13804 kB
-Pss:                8476 kB
+Rss:               13816 kB
+Pss:                8992 kB
 Shared_Clean:          0 kB
-Shared_Dirty:      10656 kB
+Shared_Dirty:       9648 kB
 Private_Clean:         0 kB
-Private_Dirty:      3148 kB
-Referenced:         5596 kB
-Anonymous:         13804 kB
+Private_Dirty:      4168 kB
+Referenced:         9160 kB
+Anonymous:         13816 kB
 LazyFree:              0 kB
 AnonHugePages:         0 kB
 ShmemPmdMapped:        0 kB
@@ -113,18 +113,18 @@
 THPeligible:		0
 ProtectionKey:         0
 VmFlags: rd wr mr mw me ac sd 
-55b92e53a000-55b92f1cc000 rw-p 00000000 00:00 0                          [heap]
-Size:              12872 kB
+55b92e53a000-55b937e4a000 rw-p 00000000 00:00 0                          [heap]
+Size:             156736 kB
 KernelPageSize:        4 kB
 MMUPageSize:           4 kB
-Rss:               12116 kB
-Pss:               12116 kB
+Rss:              140172 kB
+Pss:              140172 kB
 Shared_Clean:          0 kB
 Shared_Dirty:          0 kB
 Private_Clean:         0 kB
-Private_Dirty:     12116 kB
-Referenced:        12116 kB
-Anonymous:         12116 kB
+Private_Dirty:    140172 kB
+Referenced:       140172 kB
+Anonymous:        140172 kB
 LazyFree:              0 kB
 AnonHugePages:         0 kB
 ShmemPmdMapped:        0 kB

[cinquemb]

Update after ~3 days with latest changes with no restarts in between:

$ sudo cat /proc/8787/smaps > AfterMemInc.txt
$ diff -u BeforeMemInc.txt AfterMemInc.txt  | head -n 100
--- BeforeMemInc.txt	2020-09-11 07:53:07.415237986 +0000
+++ AfterMemInc.txt	2020-09-14 02:17:49.481545858 +0000
@@ -94,14 +94,14 @@
 Size:              14064 kB
 KernelPageSize:        4 kB
 MMUPageSize:           4 kB
-Rss:               14044 kB
-Pss:                9146 kB
+Rss:               14060 kB
+Pss:                9314 kB
 Shared_Clean:          0 kB
-Shared_Dirty:       9796 kB
+Shared_Dirty:       9492 kB
 Private_Clean:         0 kB
-Private_Dirty:      4248 kB
-Referenced:         9432 kB
-Anonymous:         14044 kB
+Private_Dirty:      4568 kB
+Referenced:        10272 kB
+Anonymous:         14060 kB
 LazyFree:              0 kB
 AnonHugePages:         0 kB
 ShmemPmdMapped:        0 kB
@@ -113,18 +113,18 @@
 THPeligible:		0
 ProtectionKey:         0
 VmFlags: rd wr mr mw me ac sd 
-556bd4375000-556bd67b7000 rw-p 00000000 00:00 0                          [heap]
-Size:              37128 kB
+556bd4375000-556be6437000 rw-p 00000000 00:00 0                          [heap]
+Size:             295688 kB
 KernelPageSize:        4 kB
 MMUPageSize:           4 kB
-Rss:               33060 kB
-Pss:               33060 kB
+Rss:              273152 kB
+Pss:              273152 kB
 Shared_Clean:          0 kB
 Shared_Dirty:          0 kB
 Private_Clean:         0 kB
-Private_Dirty:     33060 kB
-Referenced:        33060 kB
-Anonymous:         33060 kB
+Private_Dirty:    273152 kB
+Referenced:       273152 kB
+Anonymous:        273152 kB
 LazyFree:              0 kB
 AnonHugePages:         0 kB
 ShmemPmdMapped:        0 kB
@@ -136,6 +136,180004 @@