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    SubjectRe: [PATCH 6/9] readahead: clean up and simplify the code for filemap page fault readahead
    From
    2009/4/11 Andrew Morton <akpm@linux-foundation.org>:
    > On Fri, 10 Apr 2009 14:10:03 +0800
    > Wu Fengguang <fengguang.wu@intel.com> wrote:
    >
    >> @@ -1553,18 +1581,18 @@ retry_find:
    >>       if (unlikely(!PageUptodate(page)))
    >>               goto page_not_uptodate;
    >>
    >> -     /* Must recheck i_size under page lock */
    >> +     /*
    >> +      * Found the page and have a reference on it.
    >> +      * We must recheck i_size under page lock.
    >> +      */
    >>       size = (i_size_read(inode) + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
    >> -     if (unlikely(vmf->pgoff >= size)) {
    >> +     if (unlikely(offset >= size)) {
    >>               unlock_page(page);
    >>               page_cache_release(page);
    >>               return VM_FAULT_SIGBUS;
    >>       }
    >
    > This hunk broke
    > mm-update_page_reclaim_stat-is-called-from-page-fault-path.patch.
    >
    >
    > I fixed it thusly:
    >
    >        /*
    >         * Found the page and have a reference on it.
    >         * We must recheck i_size under page lock.
    >         */
    >        size = (i_size_read(inode) + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
    >        if (unlikely(offset >= size)) {
    >                unlock_page(page);
    >                page_cache_release(page);
    >                return VM_FAULT_SIGBUS;
    >        }
    > +       update_page_reclaim_stat(page);
    >        ra->prev_pos = (loff_t)offset << PAGE_CACHE_SHIFT;
    >        vmf->page = page;
    >        return ret | VM_FAULT_LOCKED;
    >
    > which seems logical to me.
    >
    > Although now I look at it, it seems that
    > mm-update_page_reclaim_stat-is-called-from-page-fault-path.patch should
    > go into 2.6.30?

    I haven't see this patch detail and I don't think
    mm-update_page_reclaim_stat-is-called-from-page-fault-path.patch
    should go into 2.6.30, but I have one question.


    > Ah.  But I have a note here that I didn't like it, because it adds lots
    > of new spinlocking to fastpaths.  So I'll leave things as they stand
    > until we have had a little talk about that.

    add?

    old code: grab zone->lru_lock via mark_page_accessed()
    new code: grab zone->lru_lock via update_reclaim_stat()

    one remove, one add.

    But I agree its lock can be removed maybe..
    I'm sorry my late work.
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