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    SubjectRe: [PATCH -mm -V3 03/21] mm, THP, swap: Support PMD swap mapping in swap_duplicate()
    Hi,

    The series up to and including this patch doesn't build. For this patch we
    need:

    diff --git a/mm/swap_state.c b/mm/swap_state.c
    index c6b3eab73fde..2f2d07627113 100644
    --- a/mm/swap_state.c
    +++ b/mm/swap_state.c
    @@ -433,7 +433,7 @@ struct page *__read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
    /*
    * Swap entry may have been freed since our caller observed it.
    */
    - err = swapcache_prepare(entry);
    + err = swapcache_prepare(entry, false);
    if (err == -EEXIST) {
    radix_tree_preload_end();
    /*

    On Wed, May 23, 2018 at 04:26:07PM +0800, Huang, Ying wrote:
    > @@ -3516,11 +3512,39 @@ static int __swap_duplicate(swp_entry_t entry, unsigned char usage)

    Two comments about this part of __swap_duplicate as long as you're moving it to
    another function:

    } else if (count || has_cache) {
    if ((count & ~COUNT_CONTINUED) < SWAP_MAP_MAX) /* #1 */
    count += usage;
    else if ((count & ~COUNT_CONTINUED) > SWAP_MAP_MAX) /* #2 */
    err = -EINVAL;
    #1: __swap_duplicate_locked might use

    VM_BUG_ON(usage != SWAP_HAS_CACHE && usage != 1);

    to document the unstated assumption that usage is 1 (otherwise count could
    overflow).

    #2: We've masked off SWAP_HAS_CACHE and COUNT_CONTINUED, and already checked
    for SWAP_MAP_BAD, so I think condition #2 always fails and can just be removed.

    > +#ifdef CONFIG_THP_SWAP
    > +static int __swap_duplicate_cluster(swp_entry_t *entry, unsigned char usage)
    ...
    > + } else {
    > + for (i = 0; i < SWAPFILE_CLUSTER; i++) {
    > +retry:
    > + err = __swap_duplicate_locked(si, offset + i, 1);

    I guess usage is assumed to be 1 at this point (__swap_duplicate_locked makes
    the same assumption). Maybe make this explicit with

    err = __swap_duplicate_locked(si, offset + i, usage);

    , use 'usage' in cluster_set_count and __swap_entry_free too, and then
    earlier have a

    VM_BUG_ON(usage != SWAP_HAS_CACHE && usage != 1);

    ?

    > +#else
    > +static inline int __swap_duplicate_cluster(swp_entry_t *entry,

    This doesn't need inline.


    Not related to your changes, but while we're here, the comment with
    SWAP_HAS_CONT in swap_count() could be deleted: I don't think there ever was a
    SWAP_HAS_CONT.

    The rest looks ok up to this point.

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