On Thu, Jun 11, 2009 at 7:21 AM, Thomas Gleixner<tglx@xxxxxxxxxxxxx> wrote:
> On Thu, 11 Jun 2009, Andreas Herrmann wrote:
>
>> Commit c9690998ef48ffefeccb91c70a7739eebdea57f9
>> (x86: memtest: remove 64-bit division) introduced following compile warning:
>>
>> arch/x86/mm/memtest.c: In function 'memtest':
>> arch/x86/mm/memtest.c:56: warning: comparison of distinct pointer types lacks a cast
>> arch/x86/mm/memtest.c:58: warning: comparison of distinct pointer types lacks a cast
>>
>> Signed-off-by: Andreas Herrmann <andreas.herrmann3@xxxxxxx>
>> ---
>> arch/x86/mm/memtest.c | 4 ++--
>> 1 files changed, 2 insertions(+), 2 deletions(-)
>>
>> Sorry.
>> Please apply.
>
> I applied it already, but zapped it right away, as it is bad style to
> do the type casting in the loops. The proper fix is below.
>
> But aside of that this code is confusing.
>
> start_phys_aligned = ALIGN(start_phys, incr);
>
> Why do we have to fiddle with the alignment. Are you really seing e820
> entries which are not 8 byte aligned ?
>
> for (p = start; p < end; p++, start_phys_aligned += incr) {
> if (*p == pattern)
> continue;
> if (start_phys_aligned == last_bad + incr) {
> last_bad += incr;
> continue;
> }
> if (start_bad)
> reserve_bad_mem(pattern, start_bad, last_bad + incr);
> start_bad = last_bad = start_phys_aligned;
> }
> if (start_bad)
> reserve_bad_mem(pattern, start_bad, last_bad + incr);
>
> I really had to look more than once to understand what the heck
> start_phys_aligned and last_bad + incr are doing. Really non
> intuitive.
>
> But the reserve_bad_mem() semantics are even more scary:
>
> - if you hit flaky memory, which gives you bad and good results here
> and there, you call reserve_bad_mem() totally unbound which is
> likely to overflow the early reservation space and panics the
> machine. You need to keep track of those events somehow (e.g. in a
> bitmap) so you can detect such problems and mark the whole affected
> region bad in one go.
if one pass found bad, it is reserved.
second pass will use find_e820_area_size() to get new range, so bad
one will not be used.
>
> - you call reserve_early() which calls __reserve_early(....,
> overrun_ok = 0) so if you do the default multi pattern scan and each
> run sees the same region of broken memory you will trigger the
> "Overlapping early reservations" panic in __reserve_early() when you
> reserve that region the second time. Why do you run the test twice
> when the first one failed already ? Also there is no need to do the
> wipeout run in that case, which will trigger it as well!
current problem in that: we could run out of res_reserve array.
solution will be make res_reserve array dynamically.
when can not find slot, need use find_e820_area to get double sized,
and copy the old to new one.
then free the old one.
YH
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