On Fri, Aug 26, 2011 at 12:06:20AM +0530, Pedanekar, Hemant wrote: > Russell King - ARM Linux wrote on Thursday, August 25, 2011 3:53 PM: > > > On Thu, Aug 25, 2011 at 09:35:07AM +0530, Pedanekar, Hemant wrote: > >> E.g., on OMAP3 with mem=32M@0x80000000 mem=8M@0x87800000 > >> > >> (CASE 1) > >> Memory: 32MB 8MB = 40MB total > >> Memory: 28408k/28408k available, 12552k reserved, 0K highmem > >> Virtual kernel memory layout: > >> vector : 0xffff0000 - 0xffff1000 ( 4 kB) > >> fixmap : 0xfff00000 - 0xfffe0000 ( 896 kB) > >> DMA : 0xffc00000 - 0xffe00000 ( 2 MB) > >> vmalloc : 0xc8800000 - 0xf8000000 ( 760 MB) > >> lowmem : 0xc0000000 - 0xc8000000 ( 128 MB) > >> modules : 0xbf000000 - 0xc0000000 ( 16 MB) > >> .text : 0xc0008000 - 0xc05ac2c8 (5777 kB) > >> .init : 0xc05ad000 - 0xc05f8780 ( 302 kB) > >> .data : 0xc05fa000 - 0xc06838d0 ( 551 kB) > >> .bss : 0xc06838f4 - 0xc0bd8a14 (5461 kB) > >> > >> Is this expected? 88MB space between two 'mem's seems to have lost. > > > > Yes. The memory layout lines gives an overview of the virtual memory > > address space _regions_. > > > > What it's saying is that the virtual addresses from 0xc0000000 - 0xc8000000 > > are used for lowmem. That may not be fully populated, but that's what > > the address range is reserved for. > > So, larger the hole, more address space will be unusable - is that correct? Correct. > >> This also > >> means vmalloc space is lower compared to when a single mem=40M is passed. > > > > Huh. Either your maths is wrong or... > > > > Here's case 1: > >> vmalloc : 0xc8800000 - 0xf8000000 ( 760 MB) And case 2: > >> vmalloc : 0xc3000000 - 0xf8000000 ( 848 MB) > > > > Looks to me like case 1, vmalloc space is _higher_ not _lower_. That's > > expected because you told the kernel it had more memory in case 1. > > Sorry, my mistake - I actually meant "vmalloc space is _smaller_ compared to > when a single mem=40M is passed" though the actual physical RAM available is > same in both the cases. Again, that's expected. We require a 1:1 relationship between virtual and physical addresses for efficiency - having non-linear translation means we'd need a lookup table, and as these translations are heavily used, that will impact performance. -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
