On Mon, 13 Jun 2011 18:11:55 -0300 Rafael Aquini <aquini@xxxxxxxxx> wrote: > Howdy Andrew, > > Sorry, for this late reply. > > On Thu, Jun 09, 2011 at 04:44:08PM -0700, Andrew Morton wrote: > > On Thu, 2 Jun 2011 23:55:57 -0300 > > Rafael Aquini <aquini@xxxxxxxxx> wrote: > > > > > When 1GB hugepages are allocated on a system, free(1) reports > > > less available memory than what really is installed in the box. > > > Also, if the total size of hugepages allocated on a system is > > > over half of the total memory size, CommitLimit becomes > > > a negative number. > > > > > > The problem is that gigantic hugepages (order > MAX_ORDER) > > > can only be allocated at boot with bootmem, thus its frames > > > are not accounted to 'totalram_pages'. However, they are > > > accounted to hugetlb_total_pages() > > > > > > What happens to turn CommitLimit into a negative number > > > is this calculation, in fs/proc/meminfo.c: > > > > > > allowed = ((totalram_pages - hugetlb_total_pages()) > > > * sysctl_overcommit_ratio / 100) + total_swap_pages; > > > > > > A similar calculation occurs in __vm_enough_memory() in mm/mmap.c. > > > > > > Also, every vm statistic which depends on 'totalram_pages' will render > > > confusing values, as if system were 'missing' some part of its memory. > > > > Is this bug serious enough to justify backporting the fix into -stable > > kernels? > > Despite not having testing it, I can think the following scenario as > troublesome: > When gigantic hugepages are allocated and sysctl_overcommit_memory == OVERCOMMIT_NEVER. > In a such situation, __vm_enough_memory() goes through the mentioned 'allowed' > calculation and might end up mistakenly returning -ENOMEM, thus forcing > the system to start reclaiming pages earlier than it would be ususal, and this could > cause detrimental impact to overall system's performance, depending on the > workload. > > Besides the aforementioned scenario, I can only think of this causing annoyances > with memory reports from /proc/meminfo and free(1). > hm, OK, thanks. That sounds a bit thin, but the patch is really simple so I stuck the cc:stable onto its changelog. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>