[PATCH] mm: add config for readahead window

[Wei Wang <wvw@google.com>]

From: Wei Wang <wvw@google.com>

Change VM_MAX_READAHEAD value from the default 128KB to a configurable
value. This will allow the readahead window to grow to a maximum size
bigger than 128KB during boot, which could benefit to sequential read
throughput and thus boot performance.

Signed-off-by: Wei Wang <wvw@google.com>
---
 include/linux/mm.h | 2 +-
 mm/Kconfig         | 8 ++++++++
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index ad06d42adb1a..d7dc6125833e 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2291,7 +2291,7 @@ int __must_check write_one_page(struct page *page);
 void task_dirty_inc(struct task_struct *tsk);
 
 /* readahead.c */
-#define VM_MAX_READAHEAD	128	/* kbytes */
+#define VM_MAX_READAHEAD	CONFIG_VM_MAX_READAHEAD_KB
 #define VM_MIN_READAHEAD	16	/* kbytes (includes current page) */
 
 int force_page_cache_readahead(struct address_space *mapping, struct file *filp,
diff --git a/mm/Kconfig b/mm/Kconfig
index c782e8fb7235..da9ff543bdb9 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -760,3 +760,11 @@ config GUP_BENCHMARK
 	  performance of get_user_pages_fast().
 
 	  See tools/testing/selftests/vm/gup_benchmark.c
+
+config VM_MAX_READAHEAD_KB
+	int "Default max readahead window size in Kilobytes"
+	default 128
+	help
+	  This sets the VM_MAX_READAHEAD value to allow the readahead window
+	  to grow to a maximum size of configured. Increasing this value will
+	  benefit sequential read throughput.
-- 
2.16.2.804.g6dcf76e118-goog