On Tue, Jun 26, 2012 at 12:41 AM, Dave Hylands <dhyla...@gmail.com> wrote:
> Hi Subbu, > > On Mon, Jun 25, 2012 at 7:45 PM, Subramaniam Appadodharana > <c.a.subraman...@gmail.com> 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. > Thanks for clarifying! Not a problem. > > > 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. > > Okay! got that! > > 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. > > No problem again. Thanks for correcting it! > -- > Dave Hylands > Shuswap, BC, Canada > http://www.davehylands.com >
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