Difference between p_vmspace quota between stable/11 and stable/10

[Konstantin Belousov]

On Thu, May 25, 2017 at 01:13:39AM -0700, Shrikanth Kamath wrote:
> Thanks for the reply Konstantin, I captured the procstat -v snapshots
> for the forked process (got the readings for both stable/10 vs
> stable/11). I am still trying to figure how to interpret these
> mappings,
> 
> In stable/11 the first few lines of procstat -v show
> 
>   PID              START                END PRT  RES PRES REF SHD FLAG TP PATH
> 
> 19933          0x8048000          0x877e000 r-x  933 1003   2   1 CN--
> vn /packages/mnt/junos-platform/sbin/dcd
> 19933          0x877e000          0x87f2000 rw-   70    0   1   0 C---
> vn /packages/mnt/junos-platform/sbin/dcd
> 19933          0x87f2000          0x8a73000 rw-   59   59   1   0 C--- df
> 19933         0xc8797000         0xc87a1000 rw-   10   10   1   0 CN-- df
> 
> The same for stable/10 show
> 
>   PID              START                END PRT  RES PRES REF SHD   FL TP PATH
> 
> 43678          0x8048000          0x8779000 r-x  943 1014   2   1 CN--
> vn /packages/mnt/junos-platform/sbin/dcd
> 43678          0x8779000          0x87ed000 rw-   70    0   1   0 C---
> vn /packages/mnt/junos-platform/sbin/dcd
> 43678          0x87ed000         0x2cc00000 rw- 145872 145872   1   0 C-S- df
> 43678         0xc8792000         0xc879c000 rw-   10   10   1   0 C--- df
> 
> 
> The third entry in two cases show a stark difference, does this
> indicated the space that was setup was much lower compared to
> stable/10?
> 
I am not sure what you mean by 'the space that was setup was much lower'.

Right after the mapping for the program' initialized data segment, follows a
BSS segment which grows into the sbrk segment.  The mapping in stable/10
map which starts at address 0x87ed000 looks like grown sbrk segment due
to this.  System does not mmap() something there, unless mmap is explicitely
asked to, by the 'address' argument, and perhaps MAP_FIXED flag.

Note that even in stable/10, jemalloc(3) uses mmap and not sbrk, so I
have no idea what that mapping is.  Either you reconfigured jemalloc()
to use sbrk, or called sbrk in the program explicitely, or called mmap()
with the address hint in sbrk area.

You should ktrace your program to see what caused creation of the mapping.