[Dynamic buffer calc][Mellanox] Fix bug: buffer over subscription in buffer pool size calculation (sonic-net#1706)

To calculate the buffer pool size, we need to accumulate all reserved memory and than subtract the sum from total available memory. In the current implementation, one part hasn’t been added to reserved memory, which causes the buffer pool size larger than it should be.
To fix it, we need to add it to reserved memory.

- What I did
Fix buffer over subscription in the buffer pool calculation.

- How I verified it
Run regression and manual test

Signed-off-by: Stephen Sun <stephens@nvidia.com>

Author: stephenxs

cfgmgr/buffer_pool_mellanox.lua

@@ -7,6 +7,9 @@ local state_db = "6"
 
 local lossypg_reserved = 19 * 1024
 local lossypg_reserved_400g = 37 * 1024
+-- Number of 400G ports
+local port_count_400g = 0
+-- Number of lossy PG on 400G ports
 local lossypg_400g = 0
 
 local result = {}
@@ -56,8 +59,11 @@ local function iterate_all_items(all_items)
             end
             profiles[index][2] = profiles[index][2] + size
             local speed = redis.call('HGET', 'PORT_TABLE:'..port, 'speed')
-            if speed == '400000' and profile == '[BUFFER_PROFILE_TABLE:ingress_lossy_profile]' then
-                lossypg_400g = lossypg_400g + size
+            if speed == '400000' then
+                if profile == '[BUFFER_PROFILE_TABLE:ingress_lossy_profile]' then
+                    lossypg_400g = lossypg_400g + size
+                end
+                port_count_400g = port_count_400g + 1
             end
         end
     end
@@ -145,6 +151,10 @@ end
 local lossypg_extra_for_400g = (lossypg_reserved_400g - lossypg_reserved) * lossypg_400g
 accumulative_occupied_buffer = accumulative_occupied_buffer + lossypg_extra_for_400g
 
+-- Accumulate sizes for management PGs
+local accumulative_management_pg = (total_port - port_count_400g) * lossypg_reserved + port_count_400g * lossypg_reserved_400g
+accumulative_occupied_buffer = accumulative_occupied_buffer + accumulative_management_pg
+
 -- Accumulate sizes for egress mirror and management pool
 local accumulative_egress_mirror_overhead = total_port * egress_mirror_headroom
 accumulative_occupied_buffer = accumulative_occupied_buffer + accumulative_egress_mirror_overhead + mgmt_pool_size
@@ -228,8 +238,9 @@ table.insert(result, "debug:accumulative size:" .. accumulative_occupied_buffer)
 for i = 1, #statistics do
     table.insert(result, "debug:" .. statistics[i][1] .. ":" .. statistics[i][2] .. ":" .. statistics[i][3])
 end
-table.insert(result, "debug:extra_400g:" .. (lossypg_reserved_400g - lossypg_reserved) .. ":" .. lossypg_400g)
+table.insert(result, "debug:extra_400g:" .. (lossypg_reserved_400g - lossypg_reserved) .. ":" .. lossypg_400g .. ":" .. port_count_400g)
 table.insert(result, "debug:mgmt_pool:" .. mgmt_pool_size)
+table.insert(result, "debug:accumulative_mgmt_pg:" .. accumulative_management_pg)
 table.insert(result, "debug:egress_mirror:" .. accumulative_egress_mirror_overhead)
 table.insert(result, "debug:shp_enabled:" .. tostring(shp_enabled))
 table.insert(result, "debug:shp_size:" .. shp_size)