io_uring: increase IORING_MAX_ENTRIES to 32K

commit 5277deaab9f98229bdfb8d1e30019b6c25052708 upstream.

Some workloads can require far more than 4K oustanding entries. For
example memcached can have ~300K sockets over ~40 cores. Bumping the max
to 32K seems to work pretty well.
Reported-by: NDan Melnic <dmm@fb.com>
Signed-off-by: NDaniel Xu <dxu@dxuuu.xyz>
Signed-off-by: NJens Axboe <axboe@kernel.dk>
Signed-off-by: NJoseph Qi <joseph.qi@linux.alibaba.com>
Reviewed-by: NXiaoguang Wang <xiaoguang.wang@linux.alibaba.com>

fs/io_uring.c

@@ -75,7 +75,7 @@
 
 #include "internal.h"
 
-#define IORING_MAX_ENTRIES	4096
+#define IORING_MAX_ENTRIES	32768
 #define IORING_MAX_FIXED_FILES	1024
 
 struct io_uring {