mm: document why we don't set PageReadahead
If the page is already in cache, we don't set PageReadahead on it. Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Christoph Hellwig <hch@lst.de> Reviewed-by: William Kucharski <william.kucharski@oracle.com> Cc: Chao Yu <yuchao0@huawei.com> Cc: Cong Wang <xiyou.wangcong@gmail.com> Cc: Darrick J. Wong <darrick.wong@oracle.com> Cc: Dave Chinner <dchinner@redhat.com> Cc: Eric Biggers <ebiggers@google.com> Cc: Gao Xiang <gaoxiang25@huawei.com> Cc: Jaegeuk Kim <jaegeuk@kernel.org> Cc: John Hubbard <jhubbard@nvidia.com> Cc: Joseph Qi <joseph.qi@linux.alibaba.com> Cc: Junxiao Bi <junxiao.bi@oracle.com> Cc: Michal Hocko <mhocko@suse.com> Cc: Zi Yan <ziy@nvidia.com> Cc: Johannes Thumshirn <johannes.thumshirn@wdc.com> Cc: Miklos Szeredi <mszeredi@redhat.com> Link: http://lkml.kernel.org/r/20200414150233.24495-15-willy@infradead.org Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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@ -195,9 +195,12 @@ void page_cache_readahead_unbounded(struct address_space *mapping,
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if (page && !xa_is_value(page)) {
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/*
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* Page already present? Kick off the current batch of
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* contiguous pages before continuing with the next
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* batch.
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* Page already present? Kick off the current batch
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* of contiguous pages before continuing with the
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* next batch. This page may be the one we would
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* have intended to mark as Readahead, but we don't
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* have a stable reference to this page, and it's
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* not worth getting one just for that.
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*/
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read_pages(&rac, &page_pool, true);
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continue;
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