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SubjectRe: PROBLEM + POSS FIX: kernel stack overflow, xfs, many disks, heavy write load, 8k stack, x86-64
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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