Re: Why store pointers for some functions in malloc.c?
From: Otto Moerbeek
Date: Wed, 18 Oct 2023 07:28:47 +0200
> On Wed, Oct 18, 2023 at 09:23:49AM +0900, Masato Asou wrote:
>
>> Hello tech@ and otto,
>>
>> Why do only some calling functions store the pinttes in region_info as
>> below:
>>
>> static void *
>> malloc_bytes(struct dir_info *d, size_t size, void *f)
>> {
>>
>> found:
>> if (i == 0 && k == 0 && DO_STATS) {
>> struct region_info *r = find(d, bp->page);
>> STATS_SETF(r, f);
>> }
>>
>> I found following mail from otto:
>> https://marc.info/?l=openbsd-tech=168171382927798=2
>> > The null "f" values (call sites) are due to the sampling nature of
>> > small allocations. Recording all call sites of all potential leaks
>> > introduces too much overhead.
>>
>> Is this the answer to my question?
>> --
>> ASOU Masato
>
> Yes.
>
> The reason is that (in the existing code) there's only one pointer per
> region_info available to store callers. So for a chunk page (which has
> many small alocations) ony slot 0 gets recorded.
OK.
> But there's a diff I posted last week on tech@ that will change this
> so that all call sites are recorded (in a different location and only
> if D is used). It will also report more details when a write of a free
> chunk is detected. That diff could use some review/testing.
I'll checkt the your posted diff.
Thank your for your information!
--
ASOU Masato
Re: Why store pointers for some functions in malloc.c?
On Wed, Oct 18, 2023 at 09:23:49AM +0900, Masato Asou wrote:
> Hello tech@ and otto,
>
> Why do only some calling functions store the pinttes in region_info as
> below:
>
> static void *
> malloc_bytes(struct dir_info *d, size_t size, void *f)
> {
>
> found:
> if (i == 0 && k == 0 && DO_STATS) {
> struct region_info *r = find(d, bp->page);
> STATS_SETF(r, f);
> }
>
> I found following mail from otto:
> https://marc.info/?l=openbsd-tech=168171382927798=2
> > The null "f" values (call sites) are due to the sampling nature of
> > small allocations. Recording all call sites of all potential leaks
> > introduces too much overhead.
>
> Is this the answer to my question?
> --
> ASOU Masato
Yes.
The reason is that (in the existing code) there's only one pointer per
region_info available to store callers. So for a chunk page (which has
many small alocations) ony slot 0 gets recorded.
But there's a diff I posted last week on tech@ that will change this
so that all call sites are recorded (in a different location and only
if D is used). It will also report more details when a write of a free
chunk is detected. That diff could use some review/testing.
-Otto
Why store pointers for some functions in malloc.c?
Hello tech@ and otto,
Why do only some calling functions store the pinttes in region_info as
below:
static void *
malloc_bytes(struct dir_info *d, size_t size, void *f)
{
found:
if (i == 0 && k == 0 && DO_STATS) {
struct region_info *r = find(d, bp->page);
STATS_SETF(r, f);
}
I found following mail from otto:
https://marc.info/?l=openbsd-tech=168171382927798=2
> The null "f" values (call sites) are due to the sampling nature of
> small allocations. Recording all call sites of all potential leaks
> introduces too much overhead.
Is this the answer to my question?
--
ASOU Masato
