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    Subject[patch 1/2] do_no_pfn handler (was: Re: [patch] mspec - special memory driver and do_no_pfn handler)
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    >>>>> "Andrew" == Andrew Morton <akpm@osdl.org> writes:

    Andrew> Jes Sorensen <jes@sgi.com> wrote:
    >> Hi,
    >>
    >> This is an updated version of the mspec driver (special memory
    >> support), formerly known as fetchop.
    >>
    >> With this version I have implemented a do_no_pfn() handler, similar
    >> to the do_no_page() handler but for pages which are not backed by a
    >> struct page.

    Andrew> hm. Is that a superset of ->nopage? Should we be looking at
    Andrew> migrating over to ->nopfn, retire ->nopage?

    Andrew> <looks at the ghastly stuff in do_no_page>

    It wasn't designed to handle all possible cases as a do_no_page
    replacement :) My initial thought was that adding an extra op to the
    vm_operations_struct was that it wouldn't be very expensive since we
    don't allocate all that many of them.

    >> Please let me know if there are any objections or comments etc. to
    >> this approach. If preferred I can split out the do_no_pfn part into
    >> a seperate patch.

    Andrew> That would probably be best.

    Here goes - if Linus comes back with a suggestion for how to do it in
    a different fashion it may obsolete this patch, but at least until
    then.

    The cleaned up version of the actual mspec driver will be in a
    seperate mail.

    Cheers,
    Jes

    Implement do_no_pfn() for handling mapping of memory without a struct
    page backing it.

    Signed-off-by: Jes Sorensen <jes@sgi.com>

    ---
    include/linux/mm.h | 1 +
    mm/memory.c | 51 ++++++++++++++++++++++++++++++++++++++++++++++++++-
    2 files changed, 51 insertions(+), 1 deletion(-)

    Index: linux-2.6/include/linux/mm.h
    ===================================================================
    --- linux-2.6.orig/include/linux/mm.h
    +++ linux-2.6/include/linux/mm.h
    @@ -199,6 +199,7 @@
    void (*open)(struct vm_area_struct * area);
    void (*close)(struct vm_area_struct * area);
    struct page * (*nopage)(struct vm_area_struct * area, unsigned long address, int *type);
    + long (*nopfn)(struct vm_area_struct * area, unsigned long address, int *type);
    int (*populate)(struct vm_area_struct * area, unsigned long address, unsigned long len, pgprot_t prot, unsigned long pgoff, int nonblock);
    #ifdef CONFIG_NUMA
    int (*set_policy)(struct vm_area_struct *vma, struct mempolicy *new);
    Index: linux-2.6/mm/memory.c
    ===================================================================
    --- linux-2.6.orig/mm/memory.c
    +++ linux-2.6/mm/memory.c
    @@ -2148,6 +2148,51 @@
    }

    /*
    + * do_no_pfn() tries to create a new page mapping for a page without
    + * a struct_page backing it
    + *
    + * As this is called only for pages that do not currently exist, we
    + * do not need to flush old virtual caches or the TLB.
    + *
    + * We enter with non-exclusive mmap_sem (to exclude vma changes,
    + * but allow concurrent faults), and pte mapped but not yet locked.
    + * We return with mmap_sem still held, but pte unmapped and unlocked.
    + *
    + * It is expected that the ->nopfn handler always returns the same pfn
    + * for a given virtual mapping.
    + */
    +static int do_no_pfn(struct mm_struct *mm, struct vm_area_struct *vma,
    + unsigned long address, pte_t *page_table, pmd_t *pmd,
    + int write_access)
    +{
    + spinlock_t *ptl;
    + pte_t entry;
    + long pfn;
    + int ret = VM_FAULT_MINOR;
    +
    + pte_unmap(page_table);
    + BUG_ON(!(vma->vm_flags & VM_PFNMAP));
    +
    + pfn = vma->vm_ops->nopfn(vma, address & PAGE_MASK, &ret);
    + if (pfn == -ENOMEM)
    + return VM_FAULT_OOM;
    + if (pfn == -EFAULT)
    + return VM_FAULT_SIGBUS;
    + if (pfn < 0)
    + return VM_FAULT_SIGBUS;
    +
    + page_table = pte_offset_map_lock(mm, pmd, address, &ptl);
    +
    + entry = pfn_pte(pfn, vma->vm_page_prot);
    + if (write_access)
    + entry = maybe_mkwrite(pte_mkdirty(entry), vma);
    + set_pte_at(mm, address, page_table, entry);
    +
    + pte_unmap_unlock(page_table, ptl);
    + return ret;
    +}
    +
    +/*
    * Fault of a previously existing named mapping. Repopulate the pte
    * from the encoded file_pte if possible. This enables swappable
    * nonlinear vmas.
    @@ -2209,9 +2254,13 @@
    old_entry = entry = *pte;
    if (!pte_present(entry)) {
    if (pte_none(entry)) {
    - if (!vma->vm_ops || !vma->vm_ops->nopage)
    + if (!vma->vm_ops ||
    + (!vma->vm_ops->nopage && !vma->vm_ops->nopfn))
    return do_anonymous_page(mm, vma, address,
    pte, pmd, write_access);
    + if (vma->vm_ops->nopfn)
    + return do_no_pfn(mm, vma, address,
    + pte, pmd, write_access);
    return do_no_page(mm, vma, address,
    pte, pmd, write_access);
    }
    -
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