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    Subject[PATCH v10 14/25] mm: Document why we don't set PageReadahead
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    From: "Matthew Wilcox (Oracle)" <willy@infradead.org>

    If the page is already in cache, we don't set PageReadahead on it.

    Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
    Reviewed-by: Christoph Hellwig <hch@lst.de>
    Reviewed-by: William Kucharski <william.kucharski@oracle.com>
    ---
    mm/readahead.c | 9 ++++++---
    1 file changed, 6 insertions(+), 3 deletions(-)

    diff --git a/mm/readahead.c b/mm/readahead.c
    index ae231a5312cb..73cb59ed5cff 100644
    --- a/mm/readahead.c
    +++ b/mm/readahead.c
    @@ -195,9 +195,12 @@ void page_cache_readahead_unbounded(struct address_space *mapping,

    if (page && !xa_is_value(page)) {
    /*
    - * Page already present? Kick off the current batch of
    - * contiguous pages before continuing with the next
    - * batch.
    + * Page already present? Kick off the current batch
    + * of contiguous pages before continuing with the
    + * next batch. This page may be the one we would
    + * have intended to mark as Readahead, but we don't
    + * have a stable reference to this page, and it's
    + * not worth getting one just for that.
    */
    read_pages(&rac, &page_pool, true);
    continue;
    --
    2.25.1
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