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    Subject[PATCH] SwapMig: Switch error handling in migrate_pages to use -Exx
    Use -Exxx instead of numeric return codes and cleanup the code
    in migrate_pages() using -Exx error codes.

    Signed-off-by: Christoph Lameter <clameter@sgi.com>

    Index: linux-2.6.15-rc1-mm2/mm/vmscan.c
    ===================================================================
    --- linux-2.6.15-rc1-mm2.orig/mm/vmscan.c 2005-11-18 10:04:05.000000000 -0800
    +++ linux-2.6.15-rc1-mm2/mm/vmscan.c 2005-11-18 10:12:01.000000000 -0800
    @@ -608,10 +608,6 @@ int putback_lru_pages(struct list_head *
    /*
    * swapout a single page
    * page is locked upon entry, unlocked on exit
    - *
    - * return codes:
    - * 0 = complete
    - * 1 = retry
    */
    static int swap_page(struct page *page)
    {
    @@ -652,7 +648,7 @@ unlock_retry:
    unlock_page(page);

    retry:
    - return 1;
    + return -EAGAIN;
    }
    /*
    * migrate_pages
    @@ -671,6 +667,8 @@ retry:
    * is only swapping out pages and never touches the second
    * list. The direct migration patchset
    * extends this function to avoid the use of swap.
    + *
    + * Return: Number of pages not migrated when "to" ran empty.
    */
    int migrate_pages(struct list_head *from, struct list_head *to,
    struct list_head *moved, struct list_head *failed)
    @@ -681,6 +679,7 @@ int migrate_pages(struct list_head *from
    struct page *page;
    struct page *page2;
    int swapwrite = current->flags & PF_SWAPWRITE;
    + int rc;

    if (!swapwrite)
    current->flags |= PF_SWAPWRITE;
    @@ -702,11 +701,12 @@ redo:
    * use lock_page() to have a higher chance of acquiring the
    * lock.
    */
    + rc = -EAGAIN;
    if (pass > 2)
    lock_page(page);
    else
    if (TestSetPageLocked(page))
    - goto retry_later;
    + goto next;

    /*
    * Only wait on writeback if we have already done a pass where
    @@ -715,18 +715,19 @@ redo:
    if (pass > 0) {
    wait_on_page_writeback(page);
    } else {
    - if (PageWriteback(page)) {
    - unlock_page(page);
    - goto retry_later;
    - }
    + if (PageWriteback(page))
    + goto unlock_page;
    }

    + /*
    + * Anonymous pages must have swap cache references otherwise
    + * the information contained in the page maps cannot be
    + * preserved.
    + */
    if (PageAnon(page) && !PageSwapCache(page)) {
    if (!add_to_swap(page, GFP_KERNEL)) {
    - unlock_page(page);
    - list_move(&page->lru, failed);
    - nr_failed++;
    - continue;
    + rc = -ENOMEM;
    + goto unlock_page;
    }
    }

    @@ -738,8 +739,19 @@ redo:
    list_move(&page->lru, moved);
    continue;
    }
    -retry_later:
    - retry++;
    +
    +unlock_page:
    + unlock_page(page);
    +
    +next:
    + if (rc == -EAGAIN)
    + retry++;
    +
    + else if (rc) {
    + /* Permanent failure to migrate the page */
    + list_move(&page->lru, failed);
    + nr_failed++;
    + }
    }
    if (retry && pass++ < 10)
    goto redo;
    -
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