On 2013/8/1 0:55, Dave Hansen wrote: > On 07/29/2013 11:49 PM, Xishi Qiu wrote: >> I think we can remove "BUG_ON(start_pfn >= end_pfn)" in __offline_pages(), >> because in memory_block_action() "nr_pages = PAGES_PER_SECTION * sections_per_block" >> is always greater than 0. > ... >> --- a/mm/memory_hotplug.c >> +++ b/mm/memory_hotplug.c >> @@ -1472,7 +1472,6 @@ static int __ref __offline_pages(unsigned long start_pfn, >> struct zone *zone; >> struct memory_notify arg; >> >> - BUG_ON(start_pfn >= end_pfn); >> /* at least, alignment against pageblock is necessary */ >> if (!IS_ALIGNED(start_pfn, pageblock_nr_pages)) >> return -EINVAL; > > I think you're saying that you don't see a way to hit this BUG_ON() in > practice. That does appear to be true, unless sections_per_block ended > up 0 or negative. The odds of getting in to this code if > 'sections_per_block' was bogus are pretty small. > Yes, I find there is an only to hit this BUG_ON() in v3.11, and "sections_per_block" seems to be always greater than 0. > Or, is this a theoretical thing that folks might run in to when adding > new features or developing? It's in a cold path and the cost of the > check is miniscule. The original author (cc'd) also saw a need to put > this in probably because he actually ran in to this. > In v2.6.32, If info->length==0, this way may hit this BUG_ON(). acpi_memory_disable_device() remove_memory(info->start_addr, info->length) offline_pages() Later Fujitsu's patch rename this function and the BUG_ON() is unnecessary. Thanks, Xishi Qiu > In any case, it looks fairly safe to me: > > Reviewed-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> > . > -- 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>