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Subject[PATCH 20/33] readahead: initial method - expected read size
backing_dev_info.ra_expect_bytes is dynamicly updated to be the expected
read pages on start-of-file. It allows the initial readahead to be more
aggressive and hence efficient.


Signed-off-by: Wu Fengguang <wfg@mail.ustc.edu.cn>
---
fs/file_table.c | 7 ++++++
include/linux/mm.h | 1
mm/readahead.c | 55 +++++++++++++++++++++++++++++++++++++++++++++++++++++
3 files changed, 63 insertions(+)
--- linux-2.6.17-rc4-mm3.orig/include/linux/mm.h
+++ linux-2.6.17-rc4-mm3/include/linux/mm.h
@@ -1032,6 +1032,7 @@ unsigned long page_cache_readahead(struc
void handle_ra_miss(struct address_space *mapping,
struct file_ra_state *ra, pgoff_t offset);
unsigned long max_sane_readahead(unsigned long nr);
+void fastcall readahead_close(struct file *file);

#ifdef CONFIG_ADAPTIVE_READAHEAD
extern int readahead_ratio;
--- linux-2.6.17-rc4-mm3.orig/fs/file_table.c
+++ linux-2.6.17-rc4-mm3/fs/file_table.c
@@ -12,6 +12,7 @@
#include <linux/init.h>
#include <linux/module.h>
#include <linux/smp_lock.h>
+#include <linux/mm.h>
#include <linux/fs.h>
#include <linux/security.h>
#include <linux/eventpoll.h>
@@ -160,6 +161,12 @@ void fastcall __fput(struct file *file)
might_sleep();

fsnotify_close(file);
+
+#ifdef CONFIG_ADAPTIVE_READAHEAD
+ if (file->f_ra.flags & RA_FLAG_EOF)
+ readahead_close(file);
+#endif
+
/*
* The function eventpoll_release() should be the first called
* in the file cleanup chain.
--- linux-2.6.17-rc4-mm3.orig/mm/readahead.c
+++ linux-2.6.17-rc4-mm3/mm/readahead.c
@@ -1555,6 +1555,61 @@ static inline void get_readahead_bounds(
PAGES_KB(128)), *ra_max / 2);
}

+/*
+ * When closing a normal readonly file,
+ * - on cache hit: increase `backing_dev_info.ra_expect_bytes' slowly;
+ * - on cache miss: decrease it rapidly.
+ *
+ * The resulted `ra_expect_bytes' answers the question of:
+ * How many pages are expected to be read on start-of-file?
+ */
+void fastcall readahead_close(struct file *file)
+{
+ struct inode *inode = file->f_dentry->d_inode;
+ struct address_space *mapping = inode->i_mapping;
+ struct backing_dev_info *bdi = mapping->backing_dev_info;
+ unsigned long pos = file->f_pos;
+ unsigned long pgrahit = file->f_ra.cache_hits;
+ unsigned long pgaccess = 1 + pos / PAGE_CACHE_SIZE;
+ unsigned long pgcached = mapping->nrpages;
+
+ if (!pos) /* pread */
+ return;
+
+ if (pgcached > bdi->ra_pages0) /* excessive reads */
+ return;
+
+ if (pgaccess >= pgcached) {
+ if (bdi->ra_expect_bytes < bdi->ra_pages0 * PAGE_CACHE_SIZE)
+ bdi->ra_expect_bytes += pgcached * PAGE_CACHE_SIZE / 8;
+
+ debug_inc(initial_ra_hit);
+ dprintk("initial_ra_hit on file %s size %lluK "
+ "pos %lu by %s(%d)\n",
+ file->f_dentry->d_name.name,
+ i_size_read(inode) / 1024,
+ pos,
+ current->comm, current->pid);
+ } else {
+ unsigned long missed;
+
+ missed = (pgcached - pgaccess) * PAGE_CACHE_SIZE;
+ if (bdi->ra_expect_bytes >= missed / 2)
+ bdi->ra_expect_bytes -= missed / 2;
+
+ debug_inc(initial_ra_miss);
+ dprintk("initial_ra_miss on file %s "
+ "size %lluK cached %luK hit %luK "
+ "pos %lu by %s(%d)\n",
+ file->f_dentry->d_name.name,
+ i_size_read(inode) / 1024,
+ pgcached << (PAGE_CACHE_SHIFT - 10),
+ pgrahit << (PAGE_CACHE_SHIFT - 10),
+ pos,
+ current->comm, current->pid);
+ }
+}
+
#endif /* CONFIG_ADAPTIVE_READAHEAD */

/*
--
-
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