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    SubjectRe: [PATCH 08/11] nfs: disable data cache revalidation for swapfiles
    On Mon, Apr 16, 2012 at 09:10:04AM -0400, Fred Isaman wrote:
    > > <SNIP>
    > > -static struct nfs_page *nfs_page_find_request_locked(struct page *page)
    > > +static struct nfs_page *
    > > +nfs_page_find_request_locked(struct nfs_inode *nfsi, struct page *page)
    > >  {
    > >        struct nfs_page *req = NULL;
    > >
    > > -       if (PagePrivate(page)) {
    > > +       if (PagePrivate(page))
    > >                req = (struct nfs_page *)page_private(page);
    > > -               if (req != NULL)
    > > -                       kref_get(&req->wb_kref);
    > > +       else if (unlikely(PageSwapCache(page))) {
    > > +               struct nfs_page *freq, *t;
    > > +
    > > +               /* Linearly search the commit list for the correct req */
    > > +               list_for_each_entry_safe(freq, t, &nfsi->commit_list, wb_list) {
    > > +                       if (freq->wb_page == page) {
    > > +                               req = freq;
    > > +                               break;
    > > +                       }
    > > +               }
    > > +
    > > +               BUG_ON(req == NULL);
    >
    > I suspect I am missing something, but why is it guaranteed that the
    > req is on the commit list?
    >

    It's a fair question and a statement about what I expected to happen.
    The commit list replaces the nfs_page_tree radix tree that used to exist
    and my understanding was that the req would exist in the radix tree until
    the swap IO was completed. I expected it to be the same for the commit
    list and the BUG_ON was based on that expectation. Are there cases where
    the req would not be found?

    Thanks.

    --
    Mel Gorman
    SUSE Labs
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