On 27.4.2015 13:26, Kirill A. Shutemov wrote:
> PageTrans* helpers are always-false if THP is disabled compile-time.
> It means the fucntion will fail to detect hugetlb pages in this case.
>
> Let's use PageCompound() instead. With small tweak to how we calculate
> next low_pfn it will make function ready to see tail pages.
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
> ---
> mm/compaction.c | 25 +++++++++++++------------
> 1 file changed, 13 insertions(+), 12 deletions(-)
>
> diff --git a/mm/compaction.c b/mm/compaction.c
> index 018f08da99a2..6ef2fdf1d6b6 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -732,18 +732,18 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
> * splitting and collapsing (collapsing has already happened
> * if PageLRU is set) but the lock is not necessarily taken
> * here and it is wasteful to take it just to check transhuge.
> - * Check TransHuge without lock and skip the whole pageblock if
> - * it's either a transhuge or hugetlbfs page, as calling
> + * Check PageCompound without lock and skip the whole pageblock
> + * if it's either a transhuge or hugetlbfs page, as calling
> * compound_order() without preventing THP from splitting the
> * page underneath us may return surprising results.
> */
> - if (PageTransHuge(page)) {
> - if (!locked)
> - low_pfn = ALIGN(low_pfn + 1,
> - pageblock_nr_pages) - 1;
> + if (PageCompound(page)) {
> + int nr;
> + if (locked)
> + nr = 1 << compound_order(page);
> else
> - low_pfn += (1 << compound_order(page)) - 1;
> -
> + nr = pageblock_nr_pages;
> + low_pfn = ALIGN(low_pfn + 1, nr) - 1;
> continue;
> }
>
> @@ -763,11 +763,12 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
> if (!locked)
> break;
>
> - /* Recheck PageLRU and PageTransHuge under lock */
> + /* Recheck PageLRU and PageCompound under lock */
> if (!PageLRU(page))
> continue;
> - if (PageTransHuge(page)) {
> - low_pfn += (1 << compound_order(page)) - 1;
> + if (PageCompound(page)) {
> + int nr = 1 << compound_order(page);
> + low_pfn = ALIGN(low_pfn + 1, nr) - 1;
> continue;
> }
> }
> @@ -778,7 +779,7 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
> if (__isolate_lru_page(page, isolate_mode) != 0)
> continue;
>
> - VM_BUG_ON_PAGE(PageTransCompound(page), page);
> + VM_BUG_ON_PAGE(PageCompound(page), page);
>
> /* Successfully isolated */
> del_page_from_lru_list(page, lruvec, page_lru(page));
>
--
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