On Fri, Dec 21, 2012 at 4:59 PM, Michel Lespinasse <walken@xxxxxxxxxx> wrote:
> On Fri, Dec 21, 2012 at 4:36 PM, Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote:
>> On Thu, Dec 20, 2012 at 4:49 PM, Michel Lespinasse <walken@xxxxxxxxxx> wrote:
>>> We have many vma manipulation functions that are fast in the typical case,
>>> but can optionally be instructed to populate an unbounded number of ptes
>>> within the region they work on:
>>> - mmap with MAP_POPULATE or MAP_LOCKED flags;
>>> - remap_file_pages() with MAP_NONBLOCK not set or when working on a
>>> VM_LOCKED vma;
>>> - mmap_region() and all its wrappers when mlock(MCL_FUTURE) is in effect;
>>> - brk() when mlock(MCL_FUTURE) is in effect.
>>>
>>
>> Something's buggy here. My evil test case is stuck with lots of
>> threads spinning at 100% system time. Stack traces look like:
>>
>> [<0000000000000000>] __mlock_vma_pages_range+0x66/0x70
>> [<0000000000000000>] __mm_populate+0xf9/0x150
>> [<0000000000000000>] vm_mmap_pgoff+0x9f/0xc0
>> [<0000000000000000>] sys_mmap_pgoff+0x7e/0x150
>> [<0000000000000000>] sys_mmap+0x22/0x30
>> [<0000000000000000>] system_call_fastpath+0x16/0x1b
>> [<0000000000000000>] 0xffffffffffffffff
>>
>> perf top says:
>>
>> 38.45% [kernel] [k] __mlock_vma_pages_range
>> 33.04% [kernel] [k] __get_user_pages
>> 28.18% [kernel] [k] __mm_populate
>>
>> The tasks in question use MCL_FUTURE but not MAP_POPULATE. These
>> tasks are immune to SIGKILL.
>
> Looking into it.
>
> There seems to be a problem with mlockall - the following program
> fails in an unkillable way even before my changes:
>
> #include <sys/mman.h>
> #include <stdio.h>
> #include <stdint.h>
>
> int main(void) {
> void *p = mmap(NULL, 0x100000000000,
> PROT_READ | PROT_WRITE,
> MAP_PRIVATE | MAP_ANON | MAP_NORESERVE,
> -1, 0);
> printf("p: %p\n", p);
> mlockall(MCL_CURRENT);
> return 0;
> }
>
> I think my changes propagate this existing problem so it now shows up
> in more places :/
Hmm. I'm using MCL_FUTURE with MAP_NORESERVE, but those mappings are
not insanely large. Should MAP_NORESERVE would negate MCL_FUTURE?
I'm doing MAP_NORESERVE, PROT_NONE to prevent pages from being
allocated in the future -- I have no intention of ever using them.
The other odd thing I do is use MAP_FIXED to replace MAP_NORESERVE pages.
--Andy
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@xxxxxxxxx. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>