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Subject[PATCH 3/3] readahead: scale max readahead size depending on memory size
Scale the default max readahead size with the system memory size.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
---
block/ll_rw_blk.c | 2 +-
include/linux/fs.h | 1 +
mm/readahead.c | 32 ++++++++++++++++++++++++++++++++
3 files changed, 34 insertions(+), 1 deletion(-)
Index: linux-2.6/block/ll_rw_blk.c
===================================================================
--- linux-2.6.orig/block/ll_rw_blk.c
+++ linux-2.6/block/ll_rw_blk.c
@@ -208,7 +208,7 @@ void blk_queue_make_request(request_queu
blk_queue_max_phys_segments(q, MAX_PHYS_SEGMENTS);
blk_queue_max_hw_segments(q, MAX_HW_SEGMENTS);
q->make_request_fn = mfn;
- q->backing_dev_info.ra_pages = (VM_MAX_READAHEAD * 1024) / PAGE_CACHE_SIZE;
+ bdi_ra_init(&q->backing_dev_info);
q->backing_dev_info.state = 0;
q->backing_dev_info.capabilities = BDI_CAP_MAP_COPY;
blk_queue_max_sectors(q, SAFE_MAX_SECTORS);
Index: linux-2.6/include/linux/fs.h
===================================================================
--- linux-2.6.orig/include/linux/fs.h
+++ linux-2.6/include/linux/fs.h
@@ -1696,6 +1696,7 @@ extern long do_splice_direct(struct file

extern void
file_ra_state_init(struct file_ra_state *ra, struct address_space *mapping);
+extern void bdi_ra_init(struct backing_dev_info *bdi);
extern loff_t no_llseek(struct file *file, loff_t offset, int origin);
extern loff_t generic_file_llseek(struct file *file, loff_t offset, int origin);
extern loff_t remote_llseek(struct file *file, loff_t offset, int origin);
Index: linux-2.6/mm/readahead.c
===================================================================
--- linux-2.6.orig/mm/readahead.c
+++ linux-2.6/mm/readahead.c
@@ -42,6 +42,38 @@ file_ra_state_init(struct file_ra_state
}
EXPORT_SYMBOL_GPL(file_ra_state_init);

+static unsigned long ra_pages;
+
+static __init int readahead_init(void)
+{
+ /*
+ * Scale the max readahead window with system memory
+ *
+ * 64M: 128K
+ * 128M: 180K
+ * 256M: 256K
+ * 512M: 360K
+ * 1G: 512K
+ * 2G: 724K
+ * 4G: 1024K
+ * 8G: 1448K
+ * 16G: 2048K
+ */
+ ra_pages = int_sqrt(totalram_pages/16);
+ if (ra_pages > (2 << (20 - PAGE_SHIFT)))
+ ra_pages = 2 << (20 - PAGE_SHIFT);
+
+ return 0;
+}
+
+subsys_initcall(readahead_init);
+
+void bdi_ra_init(struct backing_dev_info *bdi)
+{
+ bdi->ra_pages = ra_pages;
+}
+EXPORT_SYMBOL(bdi_ra_init);
+
#define list_to_page(head) (list_entry((head)->prev, struct page, lru))

/**
--

-
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