Chris Mason wrote:
shrink_zone on my box isn't 500 bytes, but lets try the easy stuff
first. This is against .34, if you have any trouble applying to .32,
just add the word noinline after the word static on the function
definitions.
This makes shrink_zone disappear from my check_stack.pl output.
Basically I think the compiler is inlining the shrink_active_zone and
shrink_inactive_zone code into shrink_zone.
Hi Chris,
I hadn't seen the followup discussion on lkml until today, but this message:
http://marc.info/?l=linux-mm&m=127122143303771&w=2
allowed me to look at stack usage in our build environment. If I've
understood correctly, it seems that a build with gcc-4.4 and gcc-4.3
have very different stack usages for shrink_zone(): 0x88 versus 0x1d8.
(details below).
The reason appears to be the -fconserve-stack compilation option
specified when using 4.4, since running the cmdline from mm/.vmscan.cmd
with gcc-4.4 but *without* -fconserve-stack gives the same result as
with 4.3.
According to the discussion when the flag was added,
http://www.gossamer-threads.com/lists/linux/kernel/1131612
this flag seems to primarily affects inlining, so I double-checked the
noinline patch you sent to the list and discovered that it had been
incorrectly applied to the build tree. Correctly applying that patch to
mm/vmscan.c (and using gcc-4.3) gives a
sub $0x78,%rsp
line. I'm very sorry that this test or ours wasn't correct and I'm sorry
for sending bad info to the list.
We're currently building a kernel with gcc-4.4 and will let you know if
it blows the 8k limit or not.
Thanks for your help.
regards,
jb
$ gcc-4.3 --version
gcc-4.3 (Ubuntu 4.3.4-5ubuntu1) 4.3.4
$ gcc-4.4 --version
gcc-4.4 (Ubuntu 4.4.1-4ubuntu9) 4.4.1
$ make CC=gcc-4.4 mm/vmscan.o
$ objdump -d mm/vmscan.o | less +/shrink_zone
0000000000002830 <shrink_zone>:
2830: 55 push %rbp
2831: 48 89 e5 mov %rsp,%rbp
2834: 41 57 push %r15
2836: 41 56 push %r14
2838: 41 55 push %r13
283a: 41 54 push %r12
283c: 53 push %rbx
283d: 48 81 ec 88 00 00 00 sub $0x88,%rsp
2844: e8 00 00 00 00 callq 2849 <shrink_zone+0x19>
$ make clean
$ make CC=gcc-4.3 mm/vmscan.o
$ objdump -d mm/vmscan.o | less +/shrink_zone
0000000000001ca0 <shrink_zone>:
1ca0: 55 push %rbp
1ca1: 48 89 e5 mov %rsp,%rbp
1ca4: 41 57 push %r15
1ca6: 41 56 push %r14
1ca8: 41 55 push %r13
1caa: 41 54 push %r12
1cac: 53 push %rbx
1cad: 48 81 ec d8 01 00 00 sub $0x1d8,%rsp
1cb4: e8 00 00 00 00 callq 1cb9 <shrink_zone+0x19>
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