Adam Litke <[email protected]> wrote:
>
> Initial Post (Thu, 18 Aug 2005)
>
> Basic overcommit checking for hugetlb_file_map() based on an implementation
> used with demand faulting in SLES9.
>
> Since demand faulting can't guarantee the availability of pages at mmap time,
> this patch implements a basic sanity check to ensure that the number of huge
> pages required to satisfy the mmap are currently available. Despite the
> obvious race, I think it is a good start on doing proper accounting. I'd like
> to work towards an accounting system that mimics the semantics of normal pages
> (especially for the MAP_PRIVATE/COW case). That work is underway and builds on
> what this patch starts.
>
> Huge page shared memory segments are simpler and still maintain their commit on
> shmget semantics.
>
> Diffed against 2.6.14-rc2-git6
>
> Signed-off-by: Adam Litke <[email protected]>
> ---
> inode.c | 47 +++++++++++++++++++++++++++++++++++++++++++++++
> 1 files changed, 47 insertions(+)
> diff -upN reference/fs/hugetlbfs/inode.c current/fs/hugetlbfs/inode.c
> --- reference/fs/hugetlbfs/inode.c
> +++ current/fs/hugetlbfs/inode.c
> @@ -45,9 +45,51 @@ static struct backing_dev_info hugetlbfs
>
> int sysctl_hugetlb_shm_group;
>
> +static void huge_pagevec_release(struct pagevec *pvec);
nit: personally I prefer to move the helper function to the top of the file
rather than having to forward-declare it.
> +unsigned long
> +huge_pages_needed(struct address_space *mapping, struct vm_area_struct *vma)
> +{
What does this function do? Seems to count all the present pages within a
vma which are backed by a particular hugetlbfs file? Or something?
If so, the chosen name seems strange. And it definitely needs a decent
comment.
> + int i;
> + struct pagevec pvec;
> + unsigned long start = vma->vm_start;
> + unsigned long end = vma->vm_end;
> + unsigned long hugepages = (end - start) >> HPAGE_SHIFT;
`hugepages' is the size of the vma
> + pgoff_t next = vma->vm_pgoff;
> + pgoff_t endpg = next + ((end - start) >> PAGE_SHIFT);
> + struct inode *inode = vma->vm_file->f_dentry->d_inode;
> +
> + /*
> + * Shared memory segments are accounted for at shget time,
> + * not at shmat (when the mapping is actually created) so
> + * check here if the memory has already been accounted for.
> + */
> + if (inode->i_blocks != 0)
> + return 0;
> +
> + pagevec_init(&pvec, 0);
> + while (next < endpg) {
> + if (!pagevec_lookup(&pvec, mapping, next, PAGEVEC_SIZE))
> + break;
> + for (i = 0; i < pagevec_count(&pvec); i++) {
> + struct page *page = pvec.pages[i];
> + if (page->index > next)
> + next = page->index;
> + if (page->index >= endpg)
> + break;
> + next++;
> + hugepages--;
And we subtract one from it for each present page.
> + }
> + huge_pagevec_release(&pvec);
> + }
> + return hugepages << HPAGE_SHIFT;
> +}
So it seems to be returning the number of bytes which are still unpopulated
within this vma?
Think you can rework this code to reduce my perplexity?
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