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    SubjectRe: [PATCH] Tight check of pfn_valid on sparsemem - v4
    On Fri, Jul 30, 2010 at 07:48:00AM -0500, Christoph Lameter wrote:
    > On Thu, 29 Jul 2010, Dave Hansen wrote:
    > > SPARSEMEM_EXTREME would be a bit different. It's a 2-level lookup.
    > > You'd have 16 "section roots", each representing 256MB of address space.
    > > Each time we put memory under one of those roots, we'd fill in a
    > > 512-section second-level table, which is designed to always fit into one
    > > page. If you start at 256MB, you won't waste all those entries.
    > That is certain a solution to the !MMU case and it would work very much
    > like a page table. If you have an MMU then the vmemmap sparsemem
    > configuration can take advantage of of that to avoid the 2 level lookup.

    Looking at vmemmap sparsemem, we need to fix it as the page table
    allocation in there bypasses the arch defined page table setup.

    This causes a problem if you have 256-entry L2 page tables with no
    room for the additional Linux VM PTE support bits (such as young,
    dirty, etc), and need to glue two 256-entry L2 hardware page tables
    plus a Linux version to store its accounting in each page. See

    So this causes a problem with vmemmap:

    pte_t entry;
    void *p = vmemmap_alloc_block_buf(PAGE_SIZE, node);
    if (!p)
    return NULL;
    entry = pfn_pte(__pa(p) >> PAGE_SHIFT, PAGE_KERNEL);

    Are you willing for this stuff to be replaced by architectures as

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      Last update: 2010-07-31 17:33    [W:0.022 / U:39.572 seconds]
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