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    SubjectRe: [PATCH] HUGETLBFS: Align memory request to multiple of huge page size to avoid underallocating.
    On Mon, 27 Feb 2012 09:09:28 -0500
    Steven Truelove <steven.truelove@utoronto.ca> wrote:

    > When calling shmget with SHM_HUGETLB, shmget aligns the request size to PAGE_SIZE, but this is not sufficient. Modified hugetlb_file_setup to align requests to the huge page size.
    >
    > Signed-off-by: Steven Truelove <steven.truelove@utoronto.ca>
    > ---
    > fs/hugetlbfs/inode.c | 9 ++++++---
    > 1 files changed, 6 insertions(+), 3 deletions(-)
    >
    > diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
    > index 1e85a7a..6c23f09 100644
    > --- a/fs/hugetlbfs/inode.c
    > +++ b/fs/hugetlbfs/inode.c
    > @@ -938,6 +938,8 @@ struct file *hugetlb_file_setup(const char *name, size_t size,
    > struct path path;
    > struct dentry *root;
    > struct qstr quick_string;
    > + struct hstate *hstate;
    > + int num_pages;
    >
    > *user = NULL;
    > if (!hugetlbfs_vfsmount)
    > @@ -967,10 +969,11 @@ struct file *hugetlb_file_setup(const char *name, size_t size,
    > if (!inode)
    > goto out_dentry;
    >
    > + hstate = hstate_inode(inode);
    > + num_pages = (size + huge_page_size(hstate) - 1) >>
    > + huge_page_shift(hstate);
    > error = -ENOMEM;
    > - if (hugetlb_reserve_pages(inode, 0,
    > - size >> huge_page_shift(hstate_inode(inode)), NULL,
    > - acctflag))
    > + if (hugetlb_reserve_pages(inode, 0, num_pages, NULL, acctflag))
    > goto out_inode;
    >
    > d_instantiate(path.dentry, inode);

    A few things...

    - sys_mmap_pgoff() does the rounding up prior to calling
    hugetlb_file_setup(). ipc/shm.c:newseg() does not.

    We should be consistent here: do it in the caller or the callee,
    not both (or neither!). I guess doing it in the callee would be
    best.

    - The above code could/should have used ALIGN(). Or round_up(): the
    difference presently escapes me, even though it was so obvious that
    we left all these things undocumented.

    - What's the point in aligning the length if we don't also look at
    the start address? If that isn't a multiple of huge_page_size(), we
    will need an additional page.



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