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    SubjectRe: [PATCH v6 10/11] mm, compaction: require only min watermarks for non-costly orders
    On Tue, Aug 16, 2016 at 08:36:12AM +0200, Vlastimil Babka wrote:
    > On 08/16/2016 08:16 AM, Joonsoo Kim wrote:
    > >On Wed, Aug 10, 2016 at 11:12:25AM +0200, Vlastimil Babka wrote:
    > >>diff --git a/mm/page_alloc.c b/mm/page_alloc.c
    > >>index 621e4211ce16..a5c0f914ec00 100644
    > >>--- a/mm/page_alloc.c
    > >>+++ b/mm/page_alloc.c
    > >>@@ -2492,7 +2492,7 @@ int __isolate_free_page(struct page *page, unsigned int order)
    > >>
    > >> if (!is_migrate_isolate(mt)) {
    > >> /* Obey watermarks as if the page was being allocated */
    > >>- watermark = low_wmark_pages(zone) + (1 << order);
    > >>+ watermark = min_wmark_pages(zone) + (1UL << order);
    > >
    > >This '1 << order' also needs some comment. Why can't we use
    > >compact_gap() in this case?
    >
    > This is just short-cutting the high-order watermark check to check
    > only order-0, because we already know the high-order page exists.
    > We can't use compact_gap() as that's too high to use for a single
    > allocation watermark, since we can be already holding some free
    > pages on the list. So it would defeat the gap purpose.

    Oops. I missed that. Thanks for clarifying it.

    Thanks.

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