Re: [Qemu-devel] Fix refcounting in hugetlbfs quota handling

[Linus Torvalds]

On Wed, Aug 10, 2011 at 11:40 PM, David Gibson
<address@hidden> wrote:
>
> This patch, therefore, stores a pointer to the inode instead of the
> address_space in the page private data for hugepages.  More
> importantly it correctly adjusts the reference count on the inodes
> when they're added to the page private data.  This ensures that the
> inode (and therefore the super block) will not be freed before we use
> it from free_huge_page.

Looks sane, but I *really* want some acks from people who use/know
hugetlbfs. Who would that be? I'm adding random people who have
acked/signed-off patches to hugetlbfs recently..

             Linus

--- patch left quoted for new people ---
> Signed-off-by: David Gibson <address@hidden>
>
> Index: working-2.6/fs/hugetlbfs/inode.c
> ===================================================================
> --- working-2.6.orig/fs/hugetlbfs/inode.c       2011-08-10 16:45:47.864758406 
> +1000
> +++ working-2.6/fs/hugetlbfs/inode.c    2011-08-10 17:22:21.899638039 +1000
> @@ -874,10 +874,10 @@ out_free:
>        return -ENOMEM;
>  }
>
> -int hugetlb_get_quota(struct address_space *mapping, long delta)
> +int hugetlb_get_quota(struct inode *inode, long delta)
>  {
>        int ret = 0;
> -       struct hugetlbfs_sb_info *sbinfo = HUGETLBFS_SB(mapping->host->i_sb);
> +       struct hugetlbfs_sb_info *sbinfo = HUGETLBFS_SB(inode->i_sb);
>
>        if (sbinfo->free_blocks > -1) {
>                spin_lock(&sbinfo->stat_lock);
> @@ -891,9 +891,9 @@ int hugetlb_get_quota(struct address_spa
>        return ret;
>  }
>
> -void hugetlb_put_quota(struct address_space *mapping, long delta)
> +void hugetlb_put_quota(struct inode *inode, long delta)
>  {
> -       struct hugetlbfs_sb_info *sbinfo = HUGETLBFS_SB(mapping->host->i_sb);
> +       struct hugetlbfs_sb_info *sbinfo = HUGETLBFS_SB(inode->i_sb);
>
>        if (sbinfo->free_blocks > -1) {
>                spin_lock(&sbinfo->stat_lock);
> Index: working-2.6/include/linux/hugetlb.h
> ===================================================================
> --- working-2.6.orig/include/linux/hugetlb.h    2011-08-10 16:58:27.952527484 
> +1000
> +++ working-2.6/include/linux/hugetlb.h 2011-08-10 17:22:08.723572707 +1000
> @@ -171,8 +171,8 @@ extern const struct file_operations huge
>  extern const struct vm_operations_struct hugetlb_vm_ops;
>  struct file *hugetlb_file_setup(const char *name, size_t size, vm_flags_t 
> acct,
>                                struct user_struct **user, int creat_flags);
> -int hugetlb_get_quota(struct address_space *mapping, long delta);
> -void hugetlb_put_quota(struct address_space *mapping, long delta);
> +int hugetlb_get_quota(struct inode *inode, long delta);
> +void hugetlb_put_quota(struct inode *inode, long delta);
>
>  static inline int is_file_hugepages(struct file *file)
>  {
> Index: working-2.6/mm/hugetlb.c
> ===================================================================
> --- working-2.6.orig/mm/hugetlb.c       2011-08-10 16:44:12.212284092 +1000
> +++ working-2.6/mm/hugetlb.c    2011-08-10 17:21:49.603477888 +1000
> @@ -533,10 +533,12 @@ static void free_huge_page(struct page *
>         */
>        struct hstate *h = page_hstate(page);
>        int nid = page_to_nid(page);
> -       struct address_space *mapping;
> +       struct inode *inode;
>
> -       mapping = (struct address_space *) page_private(page);
> +       inode = (struct inode *) page_private(page);
>        set_page_private(page, 0);
> +       iput(inode);
> +
>        page->mapping = NULL;
>        BUG_ON(page_count(page));
>        BUG_ON(page_mapcount(page));
> @@ -551,8 +553,8 @@ static void free_huge_page(struct page *
>                enqueue_huge_page(h, page);
>        }
>        spin_unlock(&hugetlb_lock);
> -       if (mapping)
> -               hugetlb_put_quota(mapping, 1);
> +       if (inode)
> +               hugetlb_put_quota(inode, 1);
>  }
>
>  static void prep_new_huge_page(struct hstate *h, struct page *page, int nid)
> @@ -1035,7 +1037,7 @@ static struct page *alloc_huge_page(stru
>        if (chg < 0)
>                return ERR_PTR(-VM_FAULT_OOM);
>        if (chg)
> -               if (hugetlb_get_quota(inode->i_mapping, chg))
> +               if (hugetlb_get_quota(inode, chg))
>                        return ERR_PTR(-VM_FAULT_SIGBUS);
>
>        spin_lock(&hugetlb_lock);
> @@ -1045,12 +1047,12 @@ static struct page *alloc_huge_page(stru
>        if (!page) {
>                page = alloc_buddy_huge_page(h, NUMA_NO_NODE);
>                if (!page) {
> -                       hugetlb_put_quota(inode->i_mapping, chg);
> +                       hugetlb_put_quota(inode, chg);
>                        return ERR_PTR(-VM_FAULT_SIGBUS);
>                }
>        }
>
> -       set_page_private(page, (unsigned long) mapping);
> +       set_page_private(page, (unsigned long) igrab(inode));
>
>        vma_commit_reservation(h, vma, addr);
>
> @@ -2086,7 +2088,8 @@ static void hugetlb_vm_op_close(struct v
>
>                if (reserve) {
>                        hugetlb_acct_memory(h, -reserve);
> -                       hugetlb_put_quota(vma->vm_file->f_mapping, reserve);
> +                       hugetlb_put_quota(vma->vm_file->f_mapping->host,
> +                                         reserve);
>                }
>        }
>  }
> @@ -2884,7 +2887,7 @@ int hugetlb_reserve_pages(struct inode *
>                return chg;
>
>        /* There must be enough filesystem quota for the mapping */
> -       if (hugetlb_get_quota(inode->i_mapping, chg))
> +       if (hugetlb_get_quota(inode, chg))
>                return -ENOSPC;
>
>        /*
> @@ -2893,7 +2896,7 @@ int hugetlb_reserve_pages(struct inode *
>         */
>        ret = hugetlb_acct_memory(h, chg);
>        if (ret < 0) {
> -               hugetlb_put_quota(inode->i_mapping, chg);
> +               hugetlb_put_quota(inode, chg);
>                return ret;
>        }
>
> @@ -2922,7 +2925,7 @@ void hugetlb_unreserve_pages(struct inod
>        inode->i_blocks -= (blocks_per_huge_page(h) * freed);
>        spin_unlock(&inode->i_lock);
>
> -       hugetlb_put_quota(inode->i_mapping, (chg - freed));
> +       hugetlb_put_quota(inode, (chg - freed));
>        hugetlb_acct_memory(h, -(chg - freed));
>  }
>
>
> --
> David Gibson                    | I'll have my music baroque, and my code
> david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
>                                | _way_ _around_!
> http://www.ozlabs.org/~dgibson
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