On 04/17/14 at 04:01am, Atsushi Kumagai wrote: > Hello Baoquan, > > >Hi Atsushi, > > > >I have got the test machine where bug reported and did a test. The > >changed code can make elf dump successful. > > Great, thanks for your help! > However, I still have questions. > > First, what is the difference between yours and mine? > > http://lists.infradead.org/pipermail/kexec/2014-April/011535.html Yeah, you are right, it's the same on changing the code bug. I mush haven't read your patch carefully. > > My patch includes renaming some values, but the purpose looks > the same as yours. > Further, you described as below, > > >On 04/14/14 at 04:02pm, Baoquan He wrote: > >> In case elf dump, the code to calculate the cyclic buffer size is > >> not correct. Since elf need bitmap1/2, so the needed memory for > >> bufsize_cyclic need be double. Hence free size should be 40% of > >> free memory, however the needed_size which free_size is compared > >> with should be info->max_mapnr / BITPERBYTE, but not 2 times of it. > >> > >> Because of this, in case of free memory in 2nd kernel is not too much, > >> OOM will happen very often. > > but I still don't think this bug causes OOM. > Even if needed_size is calculated as so much size wrongly, bufsize_cyclic > will not exceed 40% of free memory by the check below: > > info->bufsize_cyclic = (free_size <= needed_size) ? free_size : needed_size; > > So it looks that bitmap1(40%) and bitmap2(40%) will fit in 80% of free > memory in any case. > > I may misunderstand something since your patch has an effect on this > issue in practice, could you correct me? It definitely will cause OOM. On my test machine, it has 100G memory. So per old code, its needed_size is 3200K*2 == 6.4M, if currently free memory is only 15M left, the free_size will be 15M*0.4 which is 6M. So info->bufsize_cyclic is assigned to be 6M. and only 3M is left for other use, e.g page cache, dynamic allocation. OOM will happen. > > > Thanks > Atsushi Kumagai > > >> Signed-off-by: Baoquan He <bhe at redhat.com> > >> --- > >> makedumpfile.c | 2 +- > >> 1 file changed, 1 insertion(+), 1 deletion(-) > >> > >> diff --git a/makedumpfile.c b/makedumpfile.c > >> index 75092a8..01ec516 100644 > >> --- a/makedumpfile.c > >> +++ b/makedumpfile.c > >> @@ -9010,7 +9010,7 @@ calculate_cyclic_buffer_size(void) { > >> */ > >> if (info->flag_elf_dumpfile) { > >> free_size = get_free_memory_size() * 0.4; > >> - needed_size = (info->max_mapnr * 2) / BITPERBYTE; > >> + needed_size = info->max_mapnr / BITPERBYTE; > >> } else { > >> free_size = get_free_memory_size() * 0.8; > >> needed_size = info->max_mapnr / BITPERBYTE; > >> -- > >> 1.8.5.3 > >> > >> > >> _______________________________________________ > >> kexec mailing list > >> kexec at lists.infradead.org > >> http://lists.infradead.org/mailman/listinfo/kexec
