- new entry in /proc/sys/vm/readahead_ratio;
- limit loopdev file read-ahead size to 32kb;
- limit mmap read-around size to 256kb;
- dynamic read-ahead min/max bound.
Signed-off-by: Wu Fengguang <[email protected]>
---
Documentation/sysctl/vm.txt | 14 ++++++++++++++
drivers/block/loop.c | 5 +++++
include/linux/mm.h | 5 ++++-
include/linux/sysctl.h | 1 +
kernel/sysctl.c | 11 +++++++++++
mm/filemap.c | 7 +++++++
mm/readahead.c | 31 +++++++++++++++++++++++++++++++
7 files changed, 73 insertions(+), 1 deletion(-)
--- linux-2.6.14-rc5-mm1.orig/Documentation/sysctl/vm.txt
+++ linux-2.6.14-rc5-mm1/Documentation/sysctl/vm.txt
@@ -27,6 +27,7 @@ Currently, these files are in /proc/sys/
- laptop_mode
- block_dump
- swap_prefetch
+- readahead_ratio
==============================================================
@@ -114,3 +115,16 @@ except when laptop_mode is enabled and t
Setting it to 0 disables prefetching entirely.
The default value is dependant on ramsize.
+
+==============================================================
+
+readahead_ratio
+
+This limits read-ahead size to percent of the thrashing-threshold.
+The thrashing-threshold is dynamicly estimated according to the
+_history_ read speed and system load, and used to limit the
+_future_ read-ahead request size. So you should set it to a low
+value if you have not enough memory to counteract the I/O load
+fluctuation.
+
+The default value is 50.
--- linux-2.6.14-rc5-mm1.orig/include/linux/mm.h
+++ linux-2.6.14-rc5-mm1/include/linux/mm.h
@@ -927,11 +927,14 @@ extern int filemap_populate(struct vm_ar
int write_one_page(struct page *page, int wait);
/* readahead.c */
-#define VM_MAX_READAHEAD 128 /* kbytes */
+#define VM_MAX_READAHEAD 1024 /* kbytes */
#define VM_MIN_READAHEAD 16 /* kbytes (includes current page) */
#define VM_MAX_CACHE_HIT 256 /* max pages in a row in cache before
* turning readahead off */
+/* turn on read-ahead thrashing protection if (readahead_ratio >= ##) */
+#define VM_READAHEAD_PROTECT_RATIO 80
+
int do_page_cache_readahead(struct address_space *mapping, struct file *filp,
unsigned long offset, unsigned long nr_to_read);
int force_page_cache_readahead(struct address_space *mapping, struct file *filp,
--- linux-2.6.14-rc5-mm1.orig/include/linux/sysctl.h
+++ linux-2.6.14-rc5-mm1/include/linux/sysctl.h
@@ -182,6 +182,7 @@ enum
VM_LEGACY_VA_LAYOUT=27, /* legacy/compatibility virtual address space layout */
VM_SWAP_TOKEN_TIMEOUT=28, /* default time for token time out */
VM_SWAP_PREFETCH=29, /* int: amount to swap prefetch */
+ VM_READAHEAD_RATIO=30, /* percent of read-ahead size to thrashing-threshold */
};
--- linux-2.6.14-rc5-mm1.orig/kernel/sysctl.c
+++ linux-2.6.14-rc5-mm1/kernel/sysctl.c
@@ -67,6 +67,7 @@ extern int min_free_kbytes;
extern int printk_ratelimit_jiffies;
extern int printk_ratelimit_burst;
extern int pid_max_min, pid_max_max;
+extern int readahead_ratio;
#if defined(CONFIG_X86_LOCAL_APIC) && defined(CONFIG_X86)
int unknown_nmi_panic;
@@ -869,6 +870,16 @@ static ctl_table vm_table[] = {
},
#endif
#endif
+ {
+ .ctl_name = VM_READAHEAD_RATIO,
+ .procname = "readahead_ratio",
+ .data = &readahead_ratio,
+ .maxlen = sizeof(readahead_ratio),
+ .mode = 0644,
+ .proc_handler = &proc_dointvec,
+ .strategy = &sysctl_intvec,
+ .extra1 = &zero,
+ },
{ .ctl_name = 0 }
};
--- linux-2.6.14-rc5-mm1.orig/drivers/block/loop.c
+++ linux-2.6.14-rc5-mm1/drivers/block/loop.c
@@ -768,6 +768,11 @@ static int loop_set_fd(struct loop_devic
mapping = file->f_mapping;
inode = mapping->host;
+ /*
+ * The upper layer should already do proper read-ahead,
+ * unlimited read-ahead here only ruins the cache hit rate.
+ */
+ file->f_ra.ra_pages = 32 >> (PAGE_CACHE_SHIFT - 10);
if (!(file->f_mode & FMODE_WRITE))
lo_flags |= LO_FLAGS_READ_ONLY;
--- linux-2.6.14-rc5-mm1.orig/mm/filemap.c
+++ linux-2.6.14-rc5-mm1/mm/filemap.c
@@ -1312,6 +1312,13 @@ retry_find:
if (ra_pages) {
pgoff_t start = 0;
+ /*
+ * Max read-around should be much smaller than
+ * max read-ahead.
+ * How about adding a tunable parameter for this?
+ */
+ if (ra_pages > 64)
+ ra_pages = 64;
if (pgoff > ra_pages / 2)
start = pgoff - ra_pages / 2;
do_page_cache_readahead(mapping, file, start, ra_pages);
--- linux-2.6.14-rc5-mm1.orig/mm/readahead.c
+++ linux-2.6.14-rc5-mm1/mm/readahead.c
@@ -15,6 +15,13 @@
#include <linux/backing-dev.h>
#include <linux/pagevec.h>
+/* Set look-ahead size to 1/8 of the thrashing-threshold. */
+#define LOOKAHEAD_RATIO 8
+
+/* Set read-ahead size to ##% of the thrashing-threshold. */
+int readahead_ratio = 0;
+EXPORT_SYMBOL(readahead_ratio);
+
/* Detailed classification of read-ahead behaviors. */
#define RA_CLASS_SHIFT 3
#define RA_CLASS_MASK ((1 << RA_CLASS_SHIFT) - 1)
@@ -742,6 +749,30 @@ out:
}
/*
+ * ra_size is mainly determined by:
+ * 1. sequential-start: min(KB(16 + mem_mb/16), KB(64))
+ * 2. sequential-max: min(KB(64 + mem_mb*64), KB(2048))
+ * 3. sequential: (thrashing-threshold) * readahead_ratio / 100
+ *
+ * Table of concrete numbers for 4KB page size:
+ * (inactive + free) (in MB): 4 8 16 32 64 128 256 512 1024
+ * initial ra_size (in KB): 16 16 16 16 20 24 32 48 64
+ * max ra_size (in KB): 320 576 1088 2048 2048 2048 2048 2048 2048
+ */
+static inline void get_readahead_bounds(struct file_ra_state *ra,
+ unsigned long *ra_min,
+ unsigned long *ra_max)
+{
+ unsigned long mem_mb;
+
+#define KB(size) (((size) * 1024) / PAGE_CACHE_SIZE)
+ mem_mb = nr_free_inactive() * PAGE_CACHE_SIZE / 1024 / 1024;
+ *ra_max = min(min(KB(64 + mem_mb*64), KB(2048)), ra->ra_pages);
+ *ra_min = min(min(KB(VM_MIN_READAHEAD + mem_mb/16), KB(128)), *ra_max/2);
+#undef KB
+}
+
+/*
* This is the entry point of the adaptive read-ahead logic.
*
* It is only called on two conditions:
--
-
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