D32249.id96185.diff
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	diff --git a/stand/common/bcache.c b/stand/common/bcache.c
	--- a/stand/common/bcache.c
	+++ b/stand/common/bcache.c
	@@ -238,17 +238,27 @@
	if (BCACHE_LOOKUP(bc, (daddr_t)(blk + i))) {
	bcache_misses += (nblk - i);
	complete = 0;
	- if (nblk - i > BCACHE_MINREADAHEAD && bc->ra > BCACHE_MINREADAHEAD)
	- bc->ra >>= 1; /* reduce read ahead */
	break;
	} else {
	bcache_hits++;
	}
	}

	- if (complete) { /* whole set was in cache, return it */
	+ /*
	+ * Adjust read-ahead size if appropriate. Subject to the requirement
	+ * that bc->ra must stay in between MINREADAHEAD and READAHEAD, we
	+ * increase it when we notice that readahead was useful and decrease
	+ * it when we notice that readahead was not useful.
	+ */
	+ if (complete) {
	if (bc->ra < BCACHE_READAHEAD)
	- bc->ra <<= 1; /* increase read ahead */
	+ bc->ra <<= 1; /* increase read ahead */
	+ } else {
	+ if (nblk - i > BCACHE_MINREADAHEAD && bc->ra > BCACHE_MINREADAHEAD)
	+ bc->ra >>= 1; /* reduce read ahead */
	+ }
	+
	+ if (complete) { /* whole set was in cache, return it */
	bcopy(bc->bcache_data + (bcache_blksize * BHASH(bc, blk)), buf, size);
	goto done;
	}