On 27/10/14 14:17, Tejun Heo wrote: > Hello, > > On Thu, Oct 23, 2014 at 12:18:40PM -0700, Andrew Morton wrote: >> On Thu, 23 Oct 2014 17:56:53 +0100 Zubair Lutfullah Kakakhel <Zubair.Kakakhel@xxxxxxxxxx> wrote: >> >>> The default region counts are set to 1 with a comment saying empty >>> dummy entry. >>> >>> If this is a dummy entry, should this be changed to 0? > > My memory is hazy now but I'm pretty sure there's a bunch of stuff > assuming that the array is never empty. > >>> We have faced this in mips/kernel/setup.c arch_mem_init. >>> >>> cma uses memblock. But even with cma disabled. >>> The for_each_memblock(reserved, reg) goes inside the loop. >>> Even without any reserved regions. > > Does that matter? It's a zero-length reservation. > >>> Traced it to the following, when the macro >>> for_each_memblock(memblock_type, region) is used. >>> >>> It expands to add the cnt variable. >>> >>> for (region = memblock.memblock_type.regions; \ >>> region < (memblock.memblock_type.regions + memblock.memblock_type.cnt); \ >>> region++) >>> >>> In the corner case, that there are no reserved regions. >>> Due to the default 1 value of cnt. >>> The loop under for_each_memblock still runs once. >>> >>> Even when there is no reserved region. >>> >>> Is this by design? or unintentional? > > It's by design. > >>> It might be that this loop runs an extra time every instance out there? > > The first actual entry replaces the dummy one and the last removal > makes the entry dummy again, so the dummy one exists iff that's the > only entry. I don't recall the exact details right now but the choice > was an intentional one. > > Thanks. > Thank-you for clarifying. Regards ZubairLK -- 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>