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    SubjectRe: [PATCH v17 03/21] mm/compaction: correct the comments of compact_defer_shift
    On Sat, Jul 25, 2020 at 6:00 AM Alex Shi <alex.shi@linux.alibaba.com> wrote:
    >
    > There is no compact_defer_limit. It should be compact_defer_shift in
    > use. and add compact_order_failed explanation.
    >
    > Signed-off-by: Alex Shi <alex.shi@linux.alibaba.com>
    > Cc: Andrew Morton <akpm@linux-foundation.org>
    > Cc: linux-mm@kvack.org
    > Cc: linux-kernel@vger.kernel.org
    > ---
    > include/linux/mmzone.h | 1 +
    > mm/compaction.c | 2 +-
    > 2 files changed, 2 insertions(+), 1 deletion(-)
    >
    > diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
    > index f6f884970511..14c668b7e793 100644
    > --- a/include/linux/mmzone.h
    > +++ b/include/linux/mmzone.h
    > @@ -512,6 +512,7 @@ struct zone {
    > * On compaction failure, 1<<compact_defer_shift compactions
    > * are skipped before trying again. The number attempted since
    > * last failure is tracked with compact_considered.
    > + * compact_order_failed is the minimum compaction failed order.
    > */
    > unsigned int compact_considered;
    > unsigned int compact_defer_shift;
    > diff --git a/mm/compaction.c b/mm/compaction.c
    > index 86375605faa9..cd1ef9e5e638 100644
    > --- a/mm/compaction.c
    > +++ b/mm/compaction.c
    > @@ -136,7 +136,7 @@ void __ClearPageMovable(struct page *page)
    >
    > /*
    > * Compaction is deferred when compaction fails to result in a page
    > - * allocation success. 1 << compact_defer_limit compactions are skipped up
    > + * allocation success. compact_defer_shift++, compactions are skipped up
    > * to a limit of 1 << COMPACT_MAX_DEFER_SHIFT
    > */
    > void defer_compaction(struct zone *zone, int order)

    So this doesn't read right. I wouldn't keep the "++," in the
    explanation, and if we are going to refer to a limit of "1 <<
    COMPACT_MAX_DEFER_SHIFT" then maybe this should be left as "1 <<
    compact_defer_shift".

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