Re: [Qemu-devel] [PATCH v3 24/25] tcg: Allocate a guard page after code_gen_buffer

[Richard Henderson <rth@twiddle.net>]

On 09/23/2015 01:37 PM, Peter Maydell wrote:
> On 23 September 2015 at 13:00, Richard Henderson <rth@twiddle.net> wrote:
>> I've wondered about over-allocating on the mmap path, so that we can choose the
>> hugepage aligned subregion.  But as far as I can tell, my kernel doesn't
>> allocate hugepages at all, no matter what we do.  So it seems a little silly to
>> go so far out of the way to get an aligned buffer.
>
> This raises the converse question of "why are we bothering with
> MADV_HUGEPAGE at all?" :-)

I beg your pardon -- I was merely looking in the wrong place for the info. 
/proc/pid/smap does show that nearly all of the area is using huge pages:

Main memory:
7fc130000000-7fc1b0000000 rw-p 00000000 00:00 0
Size:            2097152 kB
Rss:               88064 kB
Pss:               88064 kB
Shared_Clean:          0 kB
Shared_Dirty:          0 kB
Private_Clean:         0 kB
Private_Dirty:     88064 kB
Referenced:        88064 kB
Anonymous:         88064 kB
AnonHugePages:     88064 kB
Swap:                  0 kB
KernelPageSize:        4 kB
MMUPageSize:           4 kB
Locked:                0 kB

code_gen_buffer:
7fc1d76e6000-7fc1f76e6000 rwxp 00000000 00:00 0
Size:             524288 kB
Rss:               58472 kB
Pss:               58472 kB
Shared_Clean:          0 kB
Shared_Dirty:          0 kB
Private_Clean:         0 kB
Private_Dirty:     58472 kB
Referenced:        58472 kB
Anonymous:         58472 kB
AnonHugePages:     57344 kB
Swap:                  0 kB
KernelPageSize:        4 kB
MMUPageSize:           4 kB
Locked:                0 kB


r~