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-rw-r--r--mm/readahead.c12
1 files changed, 12 insertions, 0 deletions
diff --git a/mm/readahead.c b/mm/readahead.c
index aa1aa23..033bc13 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -547,5 +547,17 @@ page_cache_async_readahead(struct address_space *mapping,
/* do read-ahead */
ondemand_readahead(mapping, ra, filp, true, offset, req_size);
+
+#ifdef CONFIG_BLOCK
+ /*
+ * Normally the current page is !uptodate and lock_page() will be
+ * immediately called to implicitly unplug the device. However this
+ * is not always true for RAID conifgurations, where data arrives
+ * not strictly in their submission order. In this case we need to
+ * explicitly kick off the IO.
+ */
+ if (PageUptodate(page))
+ blk_run_backing_dev(mapping->backing_dev_info, NULL);
+#endif
}
EXPORT_SYMBOL_GPL(page_cache_async_readahead);
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