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    SubjectRE: FW: [PATCH 0/3] Demand faulting for huge pages
    Date
    Rohit Seth wrote on Friday, October 07, 2005 2:29 PM
    > On Fri, 2005-10-07 at 10:47 -0700, Adam Litke wrote:
    > > If I were to spend time coding up a patch to remove truncation
    > > support for hugetlbfs, would it be something other people would
    > > want to see merged as well?
    >
    > In its current form, there is very little use of huegtlb truncate
    > functionality. Currently it only allows reducing the size of hugetlb
    > backing file.
    >
    > IMO it will be useful to keep and enhance this capability so that
    > apps can dynamically reduce or increase the size of backing files
    > (for example based on availability of memory at any time).

    Yup, here is a patch to enhance that capability. It is more of bring
    ftruncate on hugetlbfs file a step closer to the same semantics for
    file on other file systems.


    ---
    Add expanding ftruncate to hugetlbfs.

    Signed-off-by: Ken Chen <kenneth.w.chen@intel.com>

    --- linux-2.6.14-rc3/fs/hugetlbfs/inode.c.orig 2005-10-07 18:07:38.131373873 -0700
    +++ linux-2.6.14-rc3/fs/hugetlbfs/inode.c 2005-10-08 00:31:15.951404405 -0700
    @@ -327,20 +327,20 @@ hugetlb_vmtruncate_list(struct prio_tree
    }
    }

    -/*
    - * Expanding truncates are not allowed.
    - */
    static int hugetlb_vmtruncate(struct inode *inode, loff_t offset)
    {
    unsigned long pgoff;
    struct address_space *mapping = inode->i_mapping;
    -
    - if (offset > inode->i_size)
    - return -EINVAL;
    + struct vm_area_struct *vma;
    + struct prio_tree_iter iter;
    + int ret = 0;

    BUG_ON(offset & ~HPAGE_MASK);
    pgoff = offset >> HPAGE_SHIFT;

    + if (offset > inode->i_size)
    + goto do_expand;
    +
    inode->i_size = offset;
    spin_lock(&mapping->i_mmap_lock);
    if (!prio_tree_empty(&mapping->i_mmap))
    @@ -348,6 +348,18 @@ static int hugetlb_vmtruncate(struct ino
    spin_unlock(&mapping->i_mmap_lock);
    truncate_hugepages(mapping, offset);
    return 0;
    +
    +do_expand:
    + spin_lock(&mapping->i_mmap_lock);
    + vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, ULONG_MAX) {
    + ret = hugetlb_prefault(mapping, vma);
    + if (ret == 0)
    + inode->i_size = offset;
    + else
    + break;
    + }
    + spin_unlock(&mapping->i_mmap_lock);
    + return ret;
    }

    static int hugetlbfs_setattr(struct dentry *dentry, struct iattr *attr)
    --- linux-2.6.14-rc3/mm/hugetlb.c.orig 2005-10-07 23:16:42.789349826 -0700
    +++ linux-2.6.14-rc3/mm/hugetlb.c 2005-10-07 23:25:04.175085872 -0700
    @@ -340,7 +340,7 @@ void zap_hugepage_range(struct vm_area_s

    int hugetlb_prefault(struct address_space *mapping, struct vm_area_struct *vma)
    {
    - struct mm_struct *mm = current->mm;
    + struct mm_struct *mm = vma->vm_mm;
    unsigned long addr;
    int ret = 0;

    @@ -360,6 +360,8 @@ int hugetlb_prefault(struct address_spac
    ret = -ENOMEM;
    goto out;
    }
    + if (pte_present(*pte))
    + continue;

    idx = ((addr - vma->vm_start) >> HPAGE_SHIFT)
    + (vma->vm_pgoff >> (HPAGE_SHIFT - PAGE_SHIFT));
    -
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