Hi Subbu, On Mon, Jun 25, 2012 at 7:45 PM, Subramaniam Appadodharana <c.a.subramaniam@xxxxxxxxx> wrote: ...snip... >> However, if you call vmalloc and lets suppose that vmalloc just >> happens to return 0xE0000000. The physical address of the first page >> might be 0xD2345000. >> >> What's important is that the physical pages which back up the vmalloc >> area all come from the kernel direct mapped area. They won't ever be >> backed by pages from high-memory. So the physical addresses will all >> be in the range 0x40000000 thru 0x5FFFFFFF. >> > This is the one that I had a completely wrong understanding of!!!!!!! > I understand from the above statement that the vmalloc'ed virtual address > will _ALWAYS_ correspond to a physical address from the lowmem region! I > was under the impression that the carved out region for the vmalloc, > is the one that would back any vmalloc'ed virtual address, which is > absolutely wrong by what you are saying. Actually, I was the one that was wrong. vmalloc pages can come from low or highmem. > Now this also means that increasing vmalloc inadvertently reduces lowmem. > Why is this designed such a way? It may or may not depending on the amount of physical memory and the size of the vmalloc space. vmalloc space will normally increase vmalloc_end, which won't reduce lowmem. If the end can't advance any further, then I believe that the start can be reduced. This will reduce lowmem, if the lowmem overlaps with vmalloc memory. > Essentially, the idea that we increase vmalloc is because we expect more > memory to be consumed via vmalloc > calls, and hence we might need more physical address backing. But increasing > vmalloc decreases low mem, which would also mean that we have less backing. > Am I missing something here too :)? No - that was my mistake. -- Dave Hylands Shuswap, BC, Canada http://www.davehylands.com _______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
