Re: [PATCH] readahead: initial method - expected read size - fix fastcall

Fengguang Wu
2006-06-06T02:57:12Z

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Voluspa,

Just updated the patch a little more, as attached :)

Would you test two simple commands by the way?

time (find / >/dev/null)
(repeat and drop the first result)

dd if=/dev/zero of=sparse bs=1M seek=5000 count=1

time cp sparse /dev/null
(repeat and drop the first result)

These commands measure the pure cpu(or software) overhead of the
readahead logics, without ever hitting the physical device. I have
no 64bit cpu numbers for them yet ;)

Thanks,
Wu

[-- Attachment #2: adaptive-readahead-2.6.17-rc5.patch --]
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--- linux-2.6.17-rc5.orig/Documentation/sysctl/vm.txt
+++ linux-2.6.17-rc5/Documentation/sysctl/vm.txt
@@ -29,6 +29,8 @@ Currently, these files are in /proc/sys/
- drop-caches
- zone_reclaim_mode
- zone_reclaim_interval
+- readahead_ratio
+- readahead_hit_rate

==============================================================

@@ -178,3 +180,38 @@ Time is set in seconds and set by defaul
Reduce the interval if undesired off node allocations occur. However, too
frequent scans will have a negative impact onoff node allocation performance.

+
+==============================================================
+
+readahead_ratio
+
+This limits readahead size to percent of the thrashing threshold.
+The thrashing threshold is dynamicly estimated from the _history_ read
+speed and system load, to deduce the _future_ readahead request size.
+
+Set it to a smaller value if you have not enough memory for all the
+concurrent readers, or the I/O loads fluctuate a lot. But if there's
+plenty of memory(>2MB per reader), a bigger value may help performance.
+
+readahead_ratio also selects the readahead logic:
+ VALUE CODE PATH
+ -------------------------------------------
+ 0 disable readahead totally
+ 1-9 select the stock readahead logic
+ 10-inf select the adaptive readahead logic
+
+The default value is 50. Reasonable values would be [50, 100].
+
+==============================================================
+
+readahead_hit_rate
+
+This is the max allowed value of (readahead-pages : accessed-pages).
+Useful only when (readahead_ratio >= 10). If the previous readahead
+request has bad hit rate, the kernel will be reluctant to do the next
+readahead.
+
+Larger values help catch more sparse access patterns. Be aware that
+readahead of the sparse patterns sacrifices memory for speed.
+
+The default value is 1. It is recommended to keep the value below 16.
--- linux-2.6.17-rc5.orig/block/ll_rw_blk.c
+++ linux-2.6.17-rc5/block/ll_rw_blk.c
@@ -249,9 +249,6 @@ 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;
- q->backing_dev_info.state = 0;
- q->backing_dev_info.capabilities = BDI_CAP_MAP_COPY;
blk_queue_max_sectors(q, SAFE_MAX_SECTORS);
blk_queue_hardsect_size(q, 512);
blk_queue_dma_alignment(q, 511);
@@ -1847,6 +1844,7 @@ request_queue_t *blk_alloc_queue_node(gf
q->kobj.ktype = &queue_ktype;
kobject_init(&q->kobj);

+ q->backing_dev_info = default_backing_dev_info;
q->backing_dev_info.unplug_io_fn = blk_backing_dev_unplug;
q->backing_dev_info.unplug_io_data = q;

@@ -3764,6 +3762,29 @@ queue_ra_store(struct request_queue *q,
return ret;
}

+static ssize_t queue_initial_ra_show(struct request_queue *q, char *page)
+{
+ int kb = q->backing_dev_info.ra_pages0 << (PAGE_CACHE_SHIFT - 10);
+
+ return queue_var_show(kb, (page));
+}
+
+static ssize_t
+queue_initial_ra_store(struct request_queue *q, const char *page, size_t count)
+{
+ unsigned long kb, ra;
+ ssize_t ret = queue_var_store(&kb, page, count);
+
+ ra = kb >> (PAGE_CACHE_SHIFT - 10);
+ q->backing_dev_info.ra_pages0 = ra;
+
+ ra = kb * 1024;
+ if (q->backing_dev_info.ra_expect_bytes > ra)
+ q->backing_dev_info.ra_expect_bytes = ra;
+
+ return ret;
+}
+
static ssize_t queue_max_sectors_show(struct request_queue *q, char *page)
{
int max_sectors_kb = q->max_sectors >> 1;
@@ -3821,6 +3842,12 @@ static struct queue_sysfs_entry queue_ra
.store = queue_ra_store,
};

+static struct queue_sysfs_entry queue_initial_ra_entry = {
+ .attr = {.name = "initial_ra_kb", .mode = S_IRUGO | S_IWUSR },
+ .show = queue_initial_ra_show,
+ .store = queue_initial_ra_store,
+};
+
static struct queue_sysfs_entry queue_max_sectors_entry = {
.attr = {.name = "max_sectors_kb", .mode = S_IRUGO | S_IWUSR },
.show = queue_max_sectors_show,
@@ -3841,6 +3868,7 @@ static struct queue_sysfs_entry queue_io
static struct attribute *default_attrs[] = {
&queue_requests_entry.attr,
&queue_ra_entry.attr,
+ &queue_initial_ra_entry.attr,
&queue_max_hw_sectors_entry.attr,
&queue_max_sectors_entry.attr,
&queue_iosched_entry.attr,
--- linux-2.6.17-rc5.orig/drivers/block/loop.c
+++ linux-2.6.17-rc5/drivers/block/loop.c
@@ -779,6 +779,12 @@ static int loop_set_fd(struct loop_devic
mapping = file->f_mapping;
inode = mapping->host;

+ /*
+ * The upper layer should already do proper look-ahead,
+ * one more look-ahead here only ruins the cache hit rate.
+ */
+ file->f_ra.flags |= RA_FLAG_NO_LOOKAHEAD;
+
if (!(file->f_mode & FMODE_WRITE))
lo_flags |= LO_FLAGS_READ_ONLY;

--- linux-2.6.17-rc5.orig/fs/file_table.c
+++ linux-2.6.17-rc5/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-rc5.orig/fs/mpage.c
+++ linux-2.6.17-rc5/fs/mpage.c
@@ -407,8 +407,10 @@ mpage_readpages(struct address_space *ma
&last_block_in_bio, &map_bh,
&first_logical_block,
get_block);
- if (!pagevec_add(&lru_pvec, page))
+ if (!pagevec_add(&lru_pvec, page)) {
+ cond_resched();
__pagevec_lru_add(&lru_pvec);
+ }
} else {
page_cache_release(page);
}
--- linux-2.6.17-rc5.orig/fs/nfsd/vfs.c
+++ linux-2.6.17-rc5/fs/nfsd/vfs.c
@@ -829,7 +829,10 @@ nfsd_vfs_read(struct svc_rqst *rqstp, st
#endif

/* Get readahead parameters */
- ra = nfsd_get_raparms(inode->i_sb->s_dev, inode->i_ino);
+ if (prefer_adaptive_readahead())
+ ra = NULL;
+ else
+ ra = nfsd_get_raparms(inode->i_sb->s_dev, inode->i_ino);

if (ra && ra->p_set)
file->f_ra = ra->p_ra;
--- linux-2.6.17-rc5.orig/include/linux/backing-dev.h
+++ linux-2.6.17-rc5/include/linux/backing-dev.h
@@ -24,6 +24,9 @@ typedef int (congested_fn)(void *, int);

struct backing_dev_info {
unsigned long ra_pages; /* max readahead in PAGE_CACHE_SIZE units */
+ unsigned long ra_pages0; /* recommended readahead on start of file */
+ unsigned long ra_expect_bytes; /* expected read size on start of file */
+ unsigned long ra_thrash_bytes; /* thrashing threshold */
unsigned long state; /* Always use atomic bitops on this */
unsigned int capabilities; /* Device capabilities */
congested_fn *congested_fn; /* Function pointer if device is md/dm */
--- linux-2.6.17-rc5.orig/include/linux/fs.h
+++ linux-2.6.17-rc5/include/linux/fs.h
@@ -613,21 +613,75 @@ struct fown_struct {

/*
* Track a single file's readahead state
+ *
+ * Diagram for the adaptive readahead logic:
+ *
+ * |--------- old chunk ------->|-------------- new chunk -------------->|
+ * +----------------------------+----------------------------------------+
+ * | # | # |
+ * +----------------------------+----------------------------------------+
+ * ^ ^ ^ ^
+ * file_ra_state.la_index .ra_index .lookahead_index .readahead_index
+ *
+ * Common used deduced sizes:
+ * |----------- readahead size ------------>|
+ * +----------------------------+----------------------------------------+
+ * | # | # |
+ * +----------------------------+----------------------------------------+
+ * |------- invoke interval ------>|-- lookahead size -->|
*/
struct file_ra_state {
- unsigned long start; /* Current window */
- unsigned long size;
- unsigned long flags; /* ra flags RA_FLAG_xxx*/
- unsigned long cache_hit; /* cache hit count*/
- unsigned long prev_page; /* Cache last read() position */
- unsigned long ahead_start; /* Ahead window */
- unsigned long ahead_size;
- unsigned long ra_pages; /* Maximum readahead window */
+ union {
+ struct { /* stock read-ahead */
+ unsigned long start; /* Current window */
+ unsigned long size;
+ unsigned long ahead_start; /* Ahead window */
+ unsigned long ahead_size;
+ unsigned long cache_hit; /* cache hit count */
+ };
+#ifdef CONFIG_ADAPTIVE_READAHEAD
+ struct { /* adaptive read-ahead */
+ pgoff_t la_index; /* old chunk */
+ pgoff_t ra_index;
+ pgoff_t lookahead_index; /* new chunk */
+ pgoff_t readahead_index;
+
+ /*
+ * Read-ahead hits.
+ * i.e. # of distinct read-ahead pages accessed.
+ *
+ * What is a read-ahead sequence?
+ * A collection of sequential read-ahead requests.
+ * To put it simple:
+ * Normally a seek starts a new sequence.
+ */
+ u16 hit0; /* for the current request */
+ u16 hit1; /* for the current sequence */
+ u16 hit2; /* for the previous sequence */
+ u16 hit3; /* for the prev-prev sequence */
+
+ /*
+ * Snapshot of the (node's) read-ahead aging value
+ * on time of I/O submission.
+ */
+ unsigned long age;
+ };
+#endif
+ };
+
+ /* mmap read-around */
unsigned long mmap_hit; /* Cache hit stat for mmap accesses */
unsigned long mmap_miss; /* Cache miss stat for mmap accesses */
+
+ unsigned long flags; /* RA_FLAG_xxx | ra_class_old | ra_class_new */
+ unsigned long prev_page; /* Cache last read() position */
+ unsigned long ra_pages; /* Maximum readahead window */
};
-#define RA_FLAG_MISS 0x01 /* a cache miss occured against this file */
-#define RA_FLAG_INCACHE 0x02 /* file is already in cache */
+#define RA_FLAG_MISS (1UL<<31) /* a cache miss occured against this file */
+#define RA_FLAG_INCACHE (1UL<<30) /* file is already in cache */
+#define RA_FLAG_MMAP (1UL<<29) /* mmaped page access */
+#define RA_FLAG_NO_LOOKAHEAD (1UL<<28) /* disable look-ahead */
+#define RA_FLAG_EOF (1UL<<27) /* readahead hits EOF */

struct file {
/*
--- linux-2.6.17-rc5.orig/include/linux/mm.h
+++ linux-2.6.17-rc5/include/linux/mm.h
@@ -955,7 +955,11 @@ extern int filemap_populate(struct vm_ar
int write_one_page(struct page *page, int wait);

/* readahead.c */
+#ifdef CONFIG_ADAPTIVE_READAHEAD
+#define VM_MAX_READAHEAD 1024 /* kbytes */
+#else
#define VM_MAX_READAHEAD 128 /* kbytes */
+#endif
#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 */
@@ -972,6 +976,33 @@ 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 readahead_close(struct file *file);
+unsigned long
+page_cache_readahead_adaptive(struct address_space *mapping,
+ struct file_ra_state *ra, struct file *filp,
+ struct page *prev_page, struct page *page,
+ pgoff_t first_index, pgoff_t index, pgoff_t last_index);
+void readahead_cache_hit(struct file_ra_state *ra, struct page *page);
+
+#ifdef CONFIG_ADAPTIVE_READAHEAD
+extern int readahead_ratio;
+#else
+#define readahead_ratio 1
+#endif /* CONFIG_ADAPTIVE_READAHEAD */
+
+static inline int prefer_adaptive_readahead(void)
+{
+ return readahead_ratio >= 10;
+}
+
+DECLARE_PER_CPU(unsigned long, readahead_aging);
+static inline void inc_readahead_aging(void)
+{
+#ifdef CONFIG_READAHEAD_SMOOTH_AGING
+ if (prefer_adaptive_readahead())
+ per_cpu(readahead_aging, raw_smp_processor_id())++;
+#endif
+}

/* Do stack extension */
extern int expand_stack(struct vm_area_struct *vma, unsigned long address);
--- linux-2.6.17-rc5.orig/include/linux/mmzone.h
+++ linux-2.6.17-rc5/include/linux/mmzone.h
@@ -162,6 +162,11 @@ struct zone {
unsigned long pages_scanned; /* since last reclaim */
int all_unreclaimable; /* All pages pinned */

+ /* The accumulated number of activities that may cause page aging,
+ * that is, make some pages closer to the tail of inactive_list.
+ */
+ unsigned long aging_total;
+
/* A count of how many reclaimers are scanning this zone */
atomic_t reclaim_in_progress;

@@ -328,6 +333,7 @@ void __get_zone_counts(unsigned long *ac
unsigned long *free, struct pglist_data *pgdat);
void get_zone_counts(unsigned long *active, unsigned long *inactive,
unsigned long *free);
+unsigned long nr_free_inactive_pages_node(int nid);
void build_all_zonelists(void);
void wakeup_kswapd(struct zone *zone, int order);
int zone_watermark_ok(struct zone *z, int order, unsigned long mark,
--- linux-2.6.17-rc5.orig/include/linux/page-flags.h
+++ linux-2.6.17-rc5/include/linux/page-flags.h
@@ -89,6 +89,7 @@
#define PG_buddy 19 /* Page is free, on buddy lists */

#define PG_uncached 20 /* Page has been mapped as uncached */
+#define PG_readahead 21 /* Reminder to do readahead */

/*
* Global page accounting. One instance per CPU. Only unsigned longs are
@@ -360,6 +361,10 @@ extern void __mod_page_state_offset(unsi
#define SetPageUncached(page) set_bit(PG_uncached, &(page)->flags)
#define ClearPageUncached(page) clear_bit(PG_uncached, &(page)->flags)

+#define PageReadahead(page) test_bit(PG_readahead, &(page)->flags)
+#define SetPageReadahead(page) set_bit(PG_readahead, &(page)->flags)
+#define TestClearPageReadahead(page) test_and_clear_bit(PG_readahead, &(page)->flags)
+
struct page; /* forward declaration */

int test_clear_page_dirty(struct page *page);
--- linux-2.6.17-rc5.orig/include/linux/pagemap.h
+++ linux-2.6.17-rc5/include/linux/pagemap.h
@@ -68,6 +68,8 @@ static inline struct page *page_cache_al

typedef int filler_t(void *, struct page *);

+extern int __probe_page(struct address_space *mapping, pgoff_t offset);
+extern int probe_page(struct address_space *mapping, pgoff_t offset);
extern struct page * find_get_page(struct address_space *mapping,
unsigned long index);
extern struct page * find_lock_page(struct address_space *mapping,
--- linux-2.6.17-rc5.orig/include/linux/radix-tree.h
+++ linux-2.6.17-rc5/include/linux/radix-tree.h
@@ -54,6 +54,10 @@ void *radix_tree_delete(struct radix_tre
unsigned int
radix_tree_gang_lookup(struct radix_tree_root *root, void **results,
unsigned long first_index, unsigned int max_items);
+unsigned long radix_tree_scan_hole_backward(struct radix_tree_root *root,
+ unsigned long index, unsigned long max_scan);
+unsigned long radix_tree_scan_hole(struct radix_tree_root *root,
+ unsigned long index, unsigned long max_scan);
int radix_tree_preload(gfp_t gfp_mask);
void radix_tree_init(void);
void *radix_tree_tag_set(struct radix_tree_root *root,
--- linux-2.6.17-rc5.orig/include/linux/sysctl.h
+++ linux-2.6.17-rc5/include/linux/sysctl.h
@@ -186,6 +186,8 @@ enum
VM_PERCPU_PAGELIST_FRACTION=30,/* int: fraction of pages in each percpu_pagelist */
VM_ZONE_RECLAIM_MODE=31, /* reclaim local zone memory before going off node */
VM_ZONE_RECLAIM_INTERVAL=32, /* time period to wait after reclaim failure */
+ VM_READAHEAD_RATIO=33, /* percent of read-ahead size to thrashing-threshold */
+ VM_READAHEAD_HIT_RATE=34, /* one accessed page legitimizes so many read-ahead pages */
};

--- linux-2.6.17-rc5.orig/include/linux/writeback.h
+++ linux-2.6.17-rc5/include/linux/writeback.h
@@ -85,6 +85,12 @@ void laptop_io_completion(void);
void laptop_sync_completion(void);
void throttle_vm_writeout(void);

+extern struct timer_list laptop_mode_wb_timer;
+static inline int laptop_spinned_down(void)
+{
+ return !timer_pending(&laptop_mode_wb_timer);
+}
+
/* These are exported to sysctl. */
extern int dirty_background_ratio;
extern int vm_dirty_ratio;
--- linux-2.6.17-rc5.orig/kernel/sysctl.c
+++ linux-2.6.17-rc5/kernel/sysctl.c
@@ -73,6 +73,12 @@ extern int pid_max_min, pid_max_max;
extern int sysctl_drop_caches;
extern int percpu_pagelist_fraction;

+#if defined(CONFIG_ADAPTIVE_READAHEAD)
+extern int readahead_ratio;
+extern int readahead_hit_rate;
+static int one = 1;
+#endif
+
#if defined(CONFIG_X86_LOCAL_APIC) && defined(CONFIG_X86)
int unknown_nmi_panic;
extern int proc_unknown_nmi_panic(ctl_table *, int, struct file *,
@@ -915,6 +921,28 @@ static ctl_table vm_table[] = {
.strategy = &sysctl_jiffies,
},
#endif
+#ifdef CONFIG_ADAPTIVE_READAHEAD
+ {
+ .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 = VM_READAHEAD_HIT_RATE,
+ .procname = "readahead_hit_rate",
+ .data = &readahead_hit_rate,
+ .maxlen = sizeof(readahead_hit_rate),
+ .mode = 0644,
+ .proc_handler = &proc_dointvec,
+ .strategy = &sysctl_intvec,
+ .extra1 = &one,
+ },
+#endif
{ .ctl_name = 0 }
};

--- linux-2.6.17-rc5.orig/lib/radix-tree.c
+++ linux-2.6.17-rc5/lib/radix-tree.c
@@ -504,6 +504,77 @@ int radix_tree_tag_get(struct radix_tree
EXPORT_SYMBOL(radix_tree_tag_get);
#endif

+static unsigned long radix_tree_scan_hole_dumb(struct radix_tree_root *root,
+ unsigned long index, unsigned long max_scan)
+{
+ unsigned long i;
+
+ for (i = 0; i < max_scan; i++) {
+ if (!radix_tree_lookup(root, index + i))
+ break;
+ if (index + i == ULONG_MAX)
+ break;
+ }
+
+ return index + i;
+}
+
+static unsigned long radix_tree_scan_hole_backward_dumb(
+ struct radix_tree_root *root,
+ unsigned long index, unsigned long max_scan)
+{
+ unsigned long i;
+
+ for (i = 0; i < max_scan; i++) {
+ if (!radix_tree_lookup(root, index - i))
+ break;
+ if (index - i == 0)
+ break;
+ }
+
+ return index - i;
+}
+
+/**
+ * radix_tree_scan_hole - scan for hole
+ * @root: radix tree root
+ * @index: index key
+ * @max_scan: advice on max items to scan (it may scan a little more)
+ *
+ * Scan forward from @index for a hole/empty item, stop when
+ * - hit hole
+ * - hit index ULONG_MAX
+ * - @max_scan or more items scanned
+ *
+ * One can be sure that (@returned_index >= @index).
+ */
+unsigned long radix_tree_scan_hole(struct radix_tree_root *root,
+ unsigned long index, unsigned long max_scan)
+{
+ return radix_tree_scan_hole_dumb(root, index, max_scan);
+}
+EXPORT_SYMBOL(radix_tree_scan_hole);
+
+/**
+ * radix_tree_scan_hole_backward - scan backward for hole
+ * @root: radix tree root
+ * @index: index key
+ * @max_scan: advice on max items to scan (it may scan a little more)
+ *
+ * Scan backward from @index for a hole/empty item, stop when
+ * - hit hole
+ * - hit index 0
+ * - @max_scan or more items scanned
+ *
+ * One can be sure that (@returned_index <= @index).
+ */
+unsigned long radix_tree_scan_hole_backward(struct radix_tree_root *root,
+ unsigned long index, unsigned long max_scan)
+{
+ return radix_tree_scan_hole_backward_dumb(root, index, max_scan);
+}
+EXPORT_SYMBOL(radix_tree_scan_hole_backward);
+
static unsigned int
__lookup(struct radix_tree_root *root, void **results, unsigned long index,
unsigned int max_items, unsigned long *next_index)
--- linux-2.6.17-rc5.orig/mm/Kconfig
+++ linux-2.6.17-rc5/mm/Kconfig
@@ -145,3 +145,65 @@ config MIGRATION
while the virtual addresses are not changed. This is useful for
example on NUMA systems to put pages nearer to the processors accessing
the page.
+
+#
+# Adaptive file readahead
+#
+config ADAPTIVE_READAHEAD
+ bool "Adaptive file readahead (EXPERIMENTAL)"
+ default y
+ depends on EXPERIMENTAL
+ help
+ Readahead is a technique employed by the kernel in an attempt
+ to improve file reading performance. If the kernel has reason
+ to believe that a particular file is being read sequentially,
+ it will attempt to read blocks from the file into memory before
+ the application requests them. When readahead works, it speeds
+ up the system's throughput, since the reading application does
+ not have to wait for its requests. When readahead fails, instead,
+ it generates useless I/O and occupies memory pages which are
+ needed for some other purpose.
+
+ The kernel already has a stock readahead logic that is well
+ understood and well tuned. This option enables a more complex and
+ feature rich one. It tries to be smart and memory efficient.
+ However, due to the great diversity of real world applications, it
+ might not fit everyone.
+
+ Please refer to Documentation/sysctl/vm.txt for tunable parameters.
+
+ It is known to work well for many desktops, file servers and
+ postgresql databases. Say Y to try it out for yourself.
+
+config DEBUG_READAHEAD
+ bool "Readahead debug and accounting"
+ default y
+ depends on ADAPTIVE_READAHEAD
+ select DEBUG_FS
+ help
+ This option injects extra code to dump detailed debug traces and do
+ readahead events accounting.
+
+ To actually get the data:
+
+ mkdir /debug
+ mount -t debug none /debug
+
+ After that you can do the following:
+
+ echo > /debug/readahead/events # reset the counters
+ cat /debug/readahead/events # check the counters
+
+ echo 1 > /debug/readahead/debug_level # start events accounting
+ echo 0 > /debug/readahead/debug_level # pause events accounting
+
+ echo 2 > /debug/readahead/debug_level # show printk traces
+ echo 3 > /debug/readahead/debug_level # show printk traces(verbose)
+ echo 1 > /debug/readahead/debug_level # stop filling my kern.log
+
+ Say N for production servers.
+
+config READAHEAD_SMOOTH_AGING
+ def_bool n if NUMA
+ default y if !NUMA
+ depends on ADAPTIVE_READAHEAD
--- linux-2.6.17-rc5.orig/mm/filemap.c
+++ linux-2.6.17-rc5/mm/filemap.c
@@ -45,6 +45,12 @@ static ssize_t
generic_file_direct_IO(int rw, struct kiocb *iocb, const struct iovec *iov,
loff_t offset, unsigned long nr_segs);

+#ifdef CONFIG_DEBUG_READAHEAD
+extern u32 debug_level;
+#else
+#define debug_level 0
+#endif /* CONFIG_DEBUG_READAHEAD */
+
/*
* Shared mappings implemented 30.11.1994. It's not fully working yet,
* though.
@@ -545,6 +551,28 @@ void fastcall __lock_page(struct page *p
EXPORT_SYMBOL(__lock_page);

/*
+ * Probing page existence.
+ */
+int __probe_page(struct address_space *mapping, pgoff_t offset)
+{
+ return !! radix_tree_lookup(&mapping->page_tree, offset);
+}
+
+/*
+ * Here we just do not bother to grab the page, it's meaningless anyway.
+ */
+int probe_page(struct address_space *mapping, pgoff_t offset)
+{
+ int exists;
+
+ read_lock_irq(&mapping->tree_lock);
+ exists = __probe_page(mapping, offset);
+ read_unlock_irq(&mapping->tree_lock);
+
+ return exists;
+}
+
+/*
* a rather lightweight function, finding and getting a reference to a
* hashed page atomically.
*/
@@ -809,10 +837,12 @@ void do_generic_mapping_read(struct addr
unsigned long prev_index;
loff_t isize;
struct page *cached_page;
+ struct page *prev_page;
int error;
struct file_ra_state ra = *_ra;

cached_page = NULL;
+ prev_page = NULL;
index = *ppos >> PAGE_CACHE_SHIFT;
next_index = index;
prev_index = ra.prev_page;
@@ -823,6 +853,10 @@ void do_generic_mapping_read(struct addr
if (!isize)
goto out;

+ if (debug_level >= 5)
+ printk(KERN_DEBUG "read-file(ino=%lu, req=%lu+%lu)\n",
+ inode->i_ino, index, last_index - index);
+
end_index = (isize - 1) >> PAGE_CACHE_SHIFT;
for (;;) {
struct page *page;
@@ -841,16 +875,47 @@ void do_generic_mapping_read(struct addr
nr = nr - offset;

cond_resched();
- if (index == next_index)
+
+ if (!prefer_adaptive_readahead() && index == next_index)
next_index = page_cache_readahead(mapping, &ra, filp,
index, last_index - index);

find_page:
page = find_get_page(mapping, index);
+ if (prefer_adaptive_readahead()) {
+ if (unlikely(page == NULL)) {
+ ra.prev_page = prev_index;
+ page_cache_readahead_adaptive(mapping, &ra,
+ filp, prev_page, NULL,
+ *ppos >> PAGE_CACHE_SHIFT,
+ index, last_index);
+ page = find_get_page(mapping, index);
+ } else if (PageReadahead(page)) {
+ ra.prev_page = prev_index;
+ page_cache_readahead_adaptive(mapping, &ra,
+ filp, prev_page, page,
+ *ppos >> PAGE_CACHE_SHIFT,
+ index, last_index);
+ }
+ }
if (unlikely(page == NULL)) {
- handle_ra_miss(mapping, &ra, index);
+ if (!prefer_adaptive_readahead())
+ handle_ra_miss(mapping, &ra, index);
goto no_cached_page;
}
+
+ if (prev_page)
+ page_cache_release(prev_page);
+ prev_page = page;
+
+ if (prefer_adaptive_readahead())
+ readahead_cache_hit(&ra, page);
+
+ if (debug_level >= 7)
+ printk(KERN_DEBUG "read-page(ino=%lu, idx=%lu, io=%s)\n",
+ inode->i_ino, index,
+ PageUptodate(page) ? "hit" : "miss");
+
if (!PageUptodate(page))
goto page_not_up_to_date;
page_ok:
@@ -885,7 +950,6 @@ page_ok:
index += offset >> PAGE_CACHE_SHIFT;
offset &= ~PAGE_CACHE_MASK;

- page_cache_release(page);
if (ret == nr && desc->count)
continue;
goto out;
@@ -897,7 +961,6 @@ page_not_up_to_date:
/* Did it get unhashed before we got the lock? */
if (!page->mapping) {
unlock_page(page);
- page_cache_release(page);
continue;
}

@@ -927,7 +990,6 @@ readpage:
* invalidate_inode_pages got it
*/
unlock_page(page);
- page_cache_release(page);
goto find_page;
}
unlock_page(page);
@@ -948,7 +1010,6 @@ readpage:
isize = i_size_read(inode);
end_index = (isize - 1) >> PAGE_CACHE_SHIFT;
if (unlikely(!isize || index > end_index)) {
- page_cache_release(page);
goto out;
}

@@ -957,7 +1018,6 @@ readpage:
if (index == end_index) {
nr = ((isize - 1) & ~PAGE_CACHE_MASK) + 1;
if (nr <= offset) {
- page_cache_release(page);
goto out;
}
}
@@ -967,7 +1027,6 @@ readpage:
readpage_error:
/* UHHUH! A synchronous read error occurred. Report it */
desc->error = error;
- page_cache_release(page);
goto out;

no_cached_page:
@@ -992,15 +1051,22 @@ no_cached_page:
}
page = cached_page;
cached_page = NULL;
+ if (prev_page)
+ page_cache_release(prev_page);
+ prev_page = page;
goto readpage;
}

out:
*_ra = ra;
+ if (prefer_adaptive_readahead())
+ _ra->prev_page = prev_index;

*ppos = ((loff_t) index << PAGE_CACHE_SHIFT) + offset;
if (cached_page)
page_cache_release(cached_page);
+ if (prev_page)
+ page_cache_release(prev_page);
if (filp)
file_accessed(filp);
}
@@ -1279,6 +1345,7 @@ struct page *filemap_nopage(struct vm_ar
unsigned long size, pgoff;
int did_readaround = 0, majmin = VM_FAULT_MINOR;

+ ra->flags |= RA_FLAG_MMAP;
pgoff = ((address-area->vm_start) >> PAGE_CACHE_SHIFT) + area->vm_pgoff;

retry_all:
@@ -1296,7 +1363,7 @@ retry_all:
*
* For sequential accesses, we use the generic readahead logic.
*/
- if (VM_SequentialReadHint(area))
+ if (!prefer_adaptive_readahead() && VM_SequentialReadHint(area))
page_cache_readahead(mapping, ra, file, pgoff, 1);

/*
@@ -1304,11 +1371,24 @@ retry_all:
*/
retry_find:
page = find_get_page(mapping, pgoff);
+ if (prefer_adaptive_readahead() && VM_SequentialReadHint(area)) {
+ if (!page) {
+ page_cache_readahead_adaptive(mapping, ra,
+ file, NULL, NULL,
+ pgoff, pgoff, pgoff + 1);
+ page = find_get_page(mapping, pgoff);
+ } else if (PageReadahead(page)) {
+ page_cache_readahead_adaptive(mapping, ra,
+ file, NULL, page,
+ pgoff, pgoff, pgoff + 1);
+ }
+ }
if (!page) {
unsigned long ra_pages;

if (VM_SequentialReadHint(area)) {
- handle_ra_miss(mapping, ra, pgoff);
+ if (!prefer_adaptive_readahead())
+ handle_ra_miss(mapping, ra, pgoff);
goto no_cached_page;
}
ra->mmap_miss++;
@@ -1345,6 +1425,16 @@ retry_find:
if (!did_readaround)
ra->mmap_hit++;

+ if (prefer_adaptive_readahead())
+ readahead_cache_hit(ra, page);
+
+ if (debug_level >= 6)
+ printk(KERN_DEBUG "read-mmap(ino=%lu, idx=%lu, hint=%s, io=%s)\n",
+ inode->i_ino, pgoff,
+ VM_RandomReadHint(area) ? "random" :
+ (VM_SequentialReadHint(area) ? "sequential" : "none"),
+ PageUptodate(page) ? "hit" : "miss");
+
/*
* Ok, found a page in the page cache, now we need to check
* that it's up-to-date.
@@ -1359,6 +1449,8 @@ success:
mark_page_accessed(page);
if (type)
*type = majmin;
+ if (prefer_adaptive_readahead())
+ ra->prev_page = page->index;
return page;

outside_data_content:
--- linux-2.6.17-rc5.orig/mm/page-writeback.c
+++ linux-2.6.17-rc5/mm/page-writeback.c
@@ -376,7 +376,7 @@ static void wb_timer_fn(unsigned long un
static void laptop_timer_fn(unsigned long unused);

static DEFINE_TIMER(wb_timer, wb_timer_fn, 0, 0);
-static DEFINE_TIMER(laptop_mode_wb_timer, laptop_timer_fn, 0, 0);
+DEFINE_TIMER(laptop_mode_wb_timer, laptop_timer_fn, 0, 0);

/*
* Periodic writeback of "old" data.
--- linux-2.6.17-rc5.orig/mm/page_alloc.c
+++ linux-2.6.17-rc5/mm/page_alloc.c
@@ -543,7 +543,7 @@ static int prep_new_page(struct page *pa
if (PageReserved(page))
return 1;

- page->flags &= ~(1 << PG_uptodate | 1 << PG_error |
+ page->flags &= ~(1 << PG_uptodate | 1 << PG_error | 1 << PG_readahead |
1 << PG_referenced | 1 << PG_arch_1 |
1 << PG_checked | 1 << PG_mappedtodisk);
set_page_private(page, 0);
@@ -1361,6 +1361,22 @@ void get_zone_counts(unsigned long *acti
}
}

+/*
+ * The node's effective length of inactive_list(s).
+ */
+unsigned long nr_free_inactive_pages_node(int nid)
+{
+ unsigned int i;
+ unsigned long sum = 0;
+ struct zone *zones = NODE_DATA(nid)->node_zones;
+
+ for (i = 0; i < MAX_NR_ZONES; i++)
+ sum += zones[i].nr_inactive +
+ zones[i].free_pages - zones[i].pages_low;
+
+ return sum;
+}
+
void si_meminfo(struct sysinfo *val)
{
val->totalram = totalram_pages;
--- linux-2.6.17-rc5.orig/mm/readahead.c
+++ linux-2.6.17-rc5/mm/readahead.c
@@ -5,6 +5,8 @@
*
* 09Apr2002 akpm@zip.com.au
* Initial version.
+ * 26May2006 Wu Fengguang <wfg@mail.ustc.edu.cn>
+ * Adaptive read-ahead framework.
*/

#include <linux/kernel.h>
@@ -14,6 +16,110 @@
#include <linux/blkdev.h>
#include <linux/backing-dev.h>
#include <linux/pagevec.h>
+#include <linux/writeback.h>
+#include <asm/div64.h>
+
+/*
+ * Convienent macros for min/max read-ahead pages.
+ * Note that MAX_RA_PAGES is rounded down, while MIN_RA_PAGES is rounded up.
+ * The latter is necessary for systems with large page size(i.e. 64k).
+ */
+#define DIV_ROUND_UP(n,d) (((n) + (d) - 1) / (d))
+#define MAX_RA_PAGES (VM_MAX_READAHEAD*1024 / PAGE_CACHE_SIZE)
+#define MIN_RA_PAGES DIV_ROUND_UP(VM_MIN_READAHEAD*1024, PAGE_CACHE_SIZE)
+
+/*
+ * Adaptive read-ahead parameters.
+ */
+
+/* Default max read-ahead size for the initial method. */
+#define INITIAL_RA_PAGES DIV_ROUND_UP(128*1024, PAGE_CACHE_SIZE)
+
+/* In laptop mode, poll delayed look-ahead on every ## pages read. */
+#define LAPTOP_POLL_INTERVAL 16
+
+/* Set look-ahead size to 1/# of the thrashing-threshold. */
+#define LOOKAHEAD_RATIO 8
+
+/* Set read-ahead size to ##% of the thrashing-threshold. */
+int readahead_ratio = 50;
+EXPORT_SYMBOL_GPL(readahead_ratio);
+
+/* Readahead as long as cache hit ratio keeps above 1/##. */
+int readahead_hit_rate = 1;
+
+/*
+ * Measures the aging process of inactive_list.
+ * Mainly increased on fresh page references to make it smooth.
+ */
+#ifdef CONFIG_READAHEAD_SMOOTH_AGING
+DEFINE_PER_CPU(unsigned long, readahead_aging);
+#endif
+
+/*
+ * Detailed classification of read-ahead behaviors.
+ */
+#define RA_CLASS_SHIFT 4
+#define RA_CLASS_MASK ((1 << RA_CLASS_SHIFT) - 1)
+enum ra_class {
+ RA_CLASS_ALL,
+ RA_CLASS_INITIAL,
+ RA_CLASS_STATE,
+ RA_CLASS_CONTEXT,
+ RA_CLASS_CONTEXT_AGGRESSIVE,
+ RA_CLASS_BACKWARD,
+ RA_CLASS_THRASHING,
+ RA_CLASS_SEEK,
+ RA_CLASS_NONE,
+ RA_CLASS_COUNT
+};
+
+#define DEBUG_READAHEAD_RADIXTREE
+
+/* Read-ahead events to be accounted. */
+enum ra_event {
+ RA_EVENT_CACHE_MISS, /* read cache misses */
+ RA_EVENT_RANDOM_READ, /* random reads */
+ RA_EVENT_IO_CONGESTION, /* i/o congestion */
+ RA_EVENT_IO_CACHE_HIT, /* canceled i/o due to cache hit */
+ RA_EVENT_IO_BLOCK, /* wait for i/o completion */
+
+ RA_EVENT_READAHEAD, /* read-ahead issued */
+ RA_EVENT_READAHEAD_HIT, /* read-ahead page hit */
+ RA_EVENT_LOOKAHEAD, /* look-ahead issued */
+ RA_EVENT_LOOKAHEAD_HIT, /* look-ahead mark hit */
+ RA_EVENT_LOOKAHEAD_NOACTION, /* look-ahead mark ignored */
+ RA_EVENT_READAHEAD_MMAP, /* read-ahead for mmap access */
+ RA_EVENT_READAHEAD_EOF, /* read-ahead reaches EOF */
+ RA_EVENT_READAHEAD_SHRINK, /* ra_size falls under previous la_size */
+ RA_EVENT_READAHEAD_THRASHING, /* read-ahead thrashing happened */
+ RA_EVENT_READAHEAD_MUTILATE, /* read-ahead mutilated by imbalanced aging */
+ RA_EVENT_READAHEAD_RESCUE, /* read-ahead rescued */
+
+ RA_EVENT_READAHEAD_CUBE,
+ RA_EVENT_COUNT
+};
+
+#ifdef CONFIG_DEBUG_READAHEAD
+u32 initial_ra_hit;
+u32 initial_ra_miss;
+u32 debug_level = 1;
+u32 disable_stateful_method = 0;
+static const char * const ra_class_name[];
+static void ra_account(struct file_ra_state *ra, enum ra_event e, int pages);
+# define debug_inc(var) do { var++; } while (0)
+# define debug_option(o) (o)
+#else
+# define ra_account(ra, e, pages) do { } while (0)
+# define debug_inc(var) do { } while (0)
+# define debug_option(o) (0)
+# define debug_level (0)
+#endif /* CONFIG_DEBUG_READAHEAD */
+
+#define dprintk(args...) \
+ do { if (debug_level >= 2) printk(KERN_DEBUG args); } while(0)
+#define ddprintk(args...) \
+ do { if (debug_level >= 3) printk(KERN_DEBUG args); } while(0)

void default_unplug_io_fn(struct backing_dev_info *bdi, struct page *page)
{
@@ -21,7 +127,10 @@ void default_unplug_io_fn(struct backing
EXPORT_SYMBOL(default_unplug_io_fn);

struct backing_dev_info default_backing_dev_info = {
- .ra_pages = (VM_MAX_READAHEAD * 1024) / PAGE_CACHE_SIZE,
+ .ra_pages = MAX_RA_PAGES,
+ .ra_pages0 = INITIAL_RA_PAGES,
+ .ra_expect_bytes = INITIAL_RA_PAGES * PAGE_CACHE_SIZE,
+ .ra_thrash_bytes = MAX_RA_PAGES * PAGE_CACHE_SIZE,
.state = 0,
.capabilities = BDI_CAP_MAP_COPY,
.unplug_io_fn = default_unplug_io_fn,
@@ -49,7 +158,7 @@ static inline unsigned long get_max_read

static inline unsigned long get_min_readahead(struct file_ra_state *ra)
{
- return (VM_MIN_READAHEAD * 1024) / PAGE_CACHE_SIZE;
+ return MIN_RA_PAGES;
}

static inline void reset_ahead_window(struct file_ra_state *ra)
@@ -145,8 +254,10 @@ int read_cache_pages(struct address_spac
continue;
}
ret = filler(data, page);
- if (!pagevec_add(&lru_pvec, page))
+ if (!pagevec_add(&lru_pvec, page)) {
+ cond_resched();
__pagevec_lru_add(&lru_pvec);
+ }
if (ret) {
while (!list_empty(pages)) {
struct page *victim;
@@ -184,8 +295,10 @@ static int read_pages(struct address_spa
page->index, GFP_KERNEL)) {
ret = mapping->a_ops->readpage(filp, page);
if (ret != AOP_TRUNCATED_PAGE) {
- if (!pagevec_add(&lru_pvec, page))
+ if (!pagevec_add(&lru_pvec, page)) {
+ cond_resched();
__pagevec_lru_add(&lru_pvec);
+ }
continue;
} /* else fall through to release */
}
@@ -268,7 +381,8 @@ out:
*/
static int
__do_page_cache_readahead(struct address_space *mapping, struct file *filp,
- pgoff_t offset, unsigned long nr_to_read)
+ pgoff_t offset, unsigned long nr_to_read,
+ unsigned long lookahead_size)
{
struct inode *inode = mapping->host;
struct page *page;
@@ -281,7 +395,7 @@ __do_page_cache_readahead(struct address
if (isize == 0)
goto out;

- end_index = ((isize - 1) >> PAGE_CACHE_SHIFT);
+ end_index = ((isize - 1) >> PAGE_CACHE_SHIFT);

/*
* Preallocate as many pages as we will need.
@@ -298,12 +412,15 @@ __do_page_cache_readahead(struct address
continue;

read_unlock_irq(&mapping->tree_lock);
+ cond_resched();
page = page_cache_alloc_cold(mapping);
read_lock_irq(&mapping->tree_lock);
if (!page)
break;
page->index = page_offset;
list_add(&page->lru, &page_pool);
+ if (page_idx == nr_to_read - lookahead_size)
+ SetPageReadahead(page);
ret++;
}
read_unlock_irq(&mapping->tree_lock);
@@ -340,7 +457,7 @@ int force_page_cache_readahead(struct ad
if (this_chunk > nr_to_read)
this_chunk = nr_to_read;
err = __do_page_cache_readahead(mapping, filp,
- offset, this_chunk);
+ offset, this_chunk, 0);
if (err < 0) {
ret = err;
break;
@@ -349,6 +466,9 @@ int force_page_cache_readahead(struct ad
offset += this_chunk;
nr_to_read -= this_chunk;
}
+
+ ra_account(NULL, RA_EVENT_READAHEAD, ret);
+
return ret;
}

@@ -384,10 +504,16 @@ static inline int check_ra_success(struc
int do_page_cache_readahead(struct address_space *mapping, struct file *filp,
pgoff_t offset, unsigned long nr_to_read)
{
+ unsigned long ret;
+
if (bdi_read_congested(mapping->backing_dev_info))
return -1;

- return __do_page_cache_readahead(mapping, filp, offset, nr_to_read);
+ ret = __do_page_cache_readahead(mapping, filp, offset, nr_to_read, 0);
+
+ ra_account(NULL, RA_EVENT_READAHEAD, ret);
+
+ return ret;
}

/*
@@ -407,7 +533,11 @@ blockable_page_cache_readahead(struct ad
if (!block && bdi_read_congested(mapping->backing_dev_info))
return 0;

- actual = __do_page_cache_readahead(mapping, filp, offset, nr_to_read);
+ actual = __do_page_cache_readahead(mapping, filp, offset, nr_to_read, 0);
+
+ ra_account(NULL, RA_EVENT_READAHEAD, actual);
+ dprintk("blockable-readahead(ino=%lu, ra=%lu+%lu) = %d\n",
+ mapping->host->i_ino, offset, nr_to_read, actual);

return check_ra_success(ra, nr_to_read, actual);
}
@@ -452,7 +582,7 @@ static int make_ahead_window(struct addr
* @req_size: hint: total size of the read which the caller is performing in
* PAGE_CACHE_SIZE units
*
- * page_cache_readahead() is the main function. If performs the adaptive
+ * page_cache_readahead() is the main function. It performs the adaptive
* readahead window size management and submits the readahead I/O.
*
* Note that @filp is purely used for passing on to the ->readpage[s]()
@@ -587,3 +717,1464 @@ unsigned long max_sane_readahead(unsigne
__get_zone_counts(&active, &inactive, &free, NODE_DATA(numa_node_id()));
return min(nr, (inactive + free) / 2);
}
+
+/*
+ * Adaptive read-ahead.
+ *
+ * Good read patterns are compact both in space and time. The read-ahead logic
+ * tries to grant larger read-ahead size to better readers under the constraint
+ * of system memory and load pressure.
+ *
+ * It employs two methods to estimate the max thrashing safe read-ahead size:
+ * 1. state based - the default one
+ * 2. context based - the failsafe one
+ * The integration of the dual methods has the merit of being agile and robust.
+ * It makes the overall design clean: special cases are handled in general by
+ * the stateless method, leaving the stateful one simple and fast.
+ *
+ * To improve throughput and decrease read delay, the logic 'looks ahead'.
+ * In most read-ahead chunks, one page will be selected and tagged with
+ * PG_readahead. Later when the page with PG_readahead is read, the logic
+ * will be notified to submit the next read-ahead chunk in advance.
+ *
+ * a read-ahead chunk
+ * +-----------------------------------------+
+ * | # PG_readahead |
+ * +-----------------------------------------+
+ * ^ When this page is read, notify me for the next read-ahead.
+ *
+ */
+
+#ifdef CONFIG_ADAPTIVE_READAHEAD
+
+/*
+ * Move pages in danger (of thrashing) to the head of inactive_list.
+ * Not expected to happen frequently.
+ */
+static unsigned long rescue_pages(struct page *page, unsigned long nr_pages)
+{
+ int pgrescue = 0;
+ pgoff_t index = page_index(page);
+ struct address_space *mapping = page_mapping(page);
+ struct page *grabbed_page = NULL;
+ struct zone *zone;
+
+ dprintk("rescue_pages(ino=%lu, index=%lu nr=%lu)\n",
+ mapping->host->i_ino, index, nr_pages);
+
+ for(;;) {
+ zone = page_zone(page);
+ spin_lock_irq(&zone->lru_lock);
+
+ if (!PageLRU(page))
+ goto out_unlock;
+
+ while (page_mapping(page) == mapping &&
+ page_index(page) == index) {
+ struct page *the_page = page;
+ page = list_entry((page)->lru.prev, struct page, lru);
+ if (!PageActive(the_page) &&
+ !PageLocked(the_page) &&
+ page_count(the_page) == 1) {
+ list_move(&the_page->lru, &zone->inactive_list);
+ pgrescue++;
+ }
+ index++;
+ if (!--nr_pages)
+ goto out_unlock;
+ }
+
+ spin_unlock_irq(&zone->lru_lock);
+ cond_resched();
+
+ if (grabbed_page)
+ page_cache_release(grabbed_page);
+ grabbed_page = page = find_get_page(mapping, index);
+ if (!page)
+ goto out;
+ }
+
+out_unlock:
+ spin_unlock_irq(&zone->lru_lock);
+out:
+ if (grabbed_page)
+ page_cache_release(grabbed_page);
+ ra_account(NULL, RA_EVENT_READAHEAD_RESCUE, pgrescue);
+ return nr_pages;
+}
+
+/*
+ * Set a new look-ahead mark at @new_index.
+ * Return 0 if the new mark is successfully set.
+ */
+static int renew_lookahead(struct address_space *mapping,
+ struct file_ra_state *ra,
+ pgoff_t index, pgoff_t new_index)
+{
+ struct page *page;
+
+ if (index == ra->lookahead_index &&
+ new_index >= ra->readahead_index)
+ return 1;
+
+ page = radix_tree_lookup(&mapping->page_tree, new_index);
+ if (!page)
+ return 1;
+
+ SetPageReadahead(page);
+ if (ra->lookahead_index == index)
+ ra->lookahead_index = new_index;
+
+ return 0;
+}
+
+/*
+ * Update `backing_dev_info.ra_thrash_bytes' to be a _biased_ average of
+ * read-ahead sizes. Which makes it an a-bit-risky(*) estimation of the
+ * _minimal_ read-ahead thrashing threshold on the device.
+ *
+ * (*) Note that being a bit risky can _help_ overall performance.
+ */
+static inline void update_ra_thrash_bytes(struct backing_dev_info *bdi,
+ unsigned long ra_size)
+{
+ ra_size <<= PAGE_CACHE_SHIFT;
+ bdi->ra_thrash_bytes = (bdi->ra_thrash_bytes < ra_size) ?
+ (ra_size + bdi->ra_thrash_bytes * 1023) / 1024:
+ (ra_size + bdi->ra_thrash_bytes * 7) / 8;
+}
+
+/*
+ * The node's accumulated aging activities.
+ */
+static unsigned long node_readahead_aging(void)
+{
+ unsigned long sum = 0;
+
+#ifdef CONFIG_READAHEAD_SMOOTH_AGING
+ unsigned long cpu;
+ cpumask_t mask = node_to_cpumask(numa_node_id());
+
+ for_each_cpu_mask(cpu, mask)
+ sum += per_cpu(readahead_aging, cpu);
+#else
+ unsigned int i;
+ struct zone *zones = NODE_DATA(numa_node_id())->node_zones;
+
+ for (i = 0; i < MAX_NR_ZONES; i++)
+ sum += zones[i].aging_total;
+#endif
+
+ return sum;
+}
+
+/*
+ * Some helpers for querying/building a read-ahead request.
+ *
+ * Diagram for some variable names used frequently:
+ *
+ * |<------- la_size ------>|
+ * +-----------------------------------------+
+ * | # |
+ * +-----------------------------------------+
+ * ra_index -->|<---------------- ra_size -------------->|
+ *
+ */
+
+static enum ra_class ra_class_new(struct file_ra_state *ra)
+{
+ return ra->flags & RA_CLASS_MASK;
+}
+
+static inline enum ra_class ra_class_old(struct file_ra_state *ra)
+{
+ return (ra->flags >> RA_CLASS_SHIFT) & RA_CLASS_MASK;
+}
+
+static unsigned long ra_readahead_size(struct file_ra_state *ra)
+{
+ return ra->readahead_index - ra->ra_index;
+}
+
+static unsigned long ra_lookahead_size(struct file_ra_state *ra)
+{
+ return ra->readahead_index - ra->lookahead_index;
+}
+
+static unsigned long ra_invoke_interval(struct file_ra_state *ra)
+{
+ return ra->lookahead_index - ra->la_index;
+}
+
+/*
+ * The read-ahead is deemed success if cache-hit-rate >= 1/readahead_hit_rate.
+ */
+static int ra_cache_hit_ok(struct file_ra_state *ra)
+{
+ return ra->hit0 * readahead_hit_rate >=
+ (ra->lookahead_index - ra->la_index);
+}
+
+/*
+ * Check if @index falls in the @ra request.
+ */
+static int ra_has_index(struct file_ra_state *ra, pgoff_t index)
+{
+ if (index < ra->la_index || index >= ra->readahead_index)
+ return 0;
+
+ if (index >= ra->ra_index)
+ return 1;
+ else
+ return -1;
+}
+
+/*
+ * Which method is issuing this read-ahead?
+ */
+static void ra_set_class(struct file_ra_state *ra,
+ enum ra_class ra_class)
+{
+ unsigned long flags_mask;
+ unsigned long flags;
+ unsigned long old_ra_class;
+
+ flags_mask = ~(RA_CLASS_MASK | (RA_CLASS_MASK << RA_CLASS_SHIFT));
+ flags = ra->flags & flags_mask;
+
+ old_ra_class = ra_class_new(ra) << RA_CLASS_SHIFT;
+
+ ra->flags = flags | old_ra_class | ra_class;
+
+ /*
+ * Add request-hit up to sequence-hit and reset the former.
+ */
+ ra->hit1 += ra->hit0;
+ ra->hit0 = 0;
+
+ /*
+ * Manage the read-ahead sequences' hit counts.
+ * - the stateful method continues any existing sequence;
+ * - all other methods starts a new one.
+ */
+ if (ra_class != RA_CLASS_STATE) {
+ ra->hit3 = ra->hit2;
+ ra->hit2 = ra->hit1;
+ ra->hit1 = 0;
+ }
+}
+
+/*
+ * Where is the old read-ahead and look-ahead?
+ */
+static void ra_set_index(struct file_ra_state *ra,
+ pgoff_t la_index, pgoff_t ra_index)
+{
+ ra->la_index = la_index;
+ ra->ra_index = ra_index;
+}
+
+/*
+ * Where is the new read-ahead and look-ahead?
+ */
+static void ra_set_size(struct file_ra_state *ra,
+ unsigned long ra_size, unsigned long la_size)
+{
+ ra->readahead_index = ra->ra_index + ra_size;
+ ra->lookahead_index = ra->readahead_index - la_size;
+}
+
+/*
+ * Submit IO for the read-ahead request in file_ra_state.
+ */
+static int ra_dispatch(struct file_ra_state *ra,
+ struct address_space *mapping, struct file *filp)
+{
+ unsigned long ra_size;
+ unsigned long la_size;
+ pgoff_t eof_index;
+ int actual;
+
+ eof_index = /* it's a past-the-end index! */
+ DIV_ROUND_UP(i_size_read(mapping->host), PAGE_CACHE_SIZE);
+
+ if (unlikely(ra->ra_index >= eof_index))
+ return 0;
+
+ /*
+ * Snap to EOF, if the request
+ * - crossed the EOF boundary;
+ * - is close to EOF(explained below).
+ *
+ * Imagine a file sized 18 pages, and we dicided to read-ahead the
+ * first 16 pages. It is highly possible that in the near future we
+ * will have to do another read-ahead for the remaining 2 pages,
+ * which is an unfavorable small I/O.
+ *
+ * So we prefer to take a bit risk to enlarge the current read-ahead,
+ * to eliminate possible future small I/O.
+ */
+ if (ra->readahead_index + ra_readahead_size(ra)/4 > eof_index) {
+ ra->readahead_index = eof_index;
+ if (ra->lookahead_index > eof_index)
+ ra->lookahead_index = eof_index;
+ if (eof_index > 1)
+ ra->flags |= RA_FLAG_EOF;
+ }
+
+ /* Disable look-ahead for loopback file. */
+ if (unlikely(ra->flags & RA_FLAG_NO_LOOKAHEAD))
+ ra->lookahead_index = ra->readahead_index;
+
+ /* Take down the current read-ahead aging value. */
+ ra->age = node_readahead_aging();
+
+ ra_size = ra_readahead_size(ra);
+ la_size = ra_lookahead_size(ra);
+ actual = __do_page_cache_readahead(mapping, filp,
+ ra->ra_index, ra_size, la_size);
+
+#ifdef CONFIG_DEBUG_READAHEAD
+ if (ra->flags & RA_FLAG_MMAP)
+ ra_account(ra, RA_EVENT_READAHEAD_MMAP, actual);
+ if (ra->readahead_index == eof_index)
+ ra_account(ra, RA_EVENT_READAHEAD_EOF, actual);
+ if (la_size)
+ ra_account(ra, RA_EVENT_LOOKAHEAD, la_size);
+ if (ra_size > actual)
+ ra_account(ra, RA_EVENT_IO_CACHE_HIT, ra_size - actual);
+ ra_account(ra, RA_EVENT_READAHEAD, actual);
+
+ if (!ra->ra_index && filp->f_dentry->d_inode) {
+ char *fn;
+ static char path[1024];
+ unsigned long size;
+
+ size = (i_size_read(filp->f_dentry->d_inode)+1023)/1024;
+ fn = d_path(filp->f_dentry, filp->f_vfsmnt, path, 1000);
+ if (!IS_ERR(fn))
+ ddprintk("ino %lu is %s size %luK by %s(%d)\n",
+ filp->f_dentry->d_inode->i_ino,
+ fn, size,
+ current->comm, current->pid);
+ }
+
+ dprintk("readahead-%s(ino=%lu, index=%lu, ra=%lu+%lu-%lu) = %d\n",
+ ra_class_name[ra_class_new(ra)],
+ mapping->host->i_ino, ra->la_index,
+ ra->ra_index, ra_size, la_size, actual);
+#endif /* CONFIG_DEBUG_READAHEAD */
+
+ return actual;
+}
+
+/*
+ * Deduce the read-ahead/look-ahead size from primitive values.
+ *
+ * Input:
+ * - @ra_size stores the estimated thrashing-threshold.
+ * - @la_size stores the look-ahead size of previous request.
+ */
+static int adjust_rala(unsigned long ra_max,
+ unsigned long *ra_size, unsigned long *la_size)
+{
+ /*
+ * Substract the old look-ahead to get real safe size for the next
+ * read-ahead request.
+ */
+ if (*ra_size > *la_size)
+ *ra_size -= *la_size;
+ else {
+ ra_account(NULL, RA_EVENT_READAHEAD_SHRINK, *ra_size);
+ return 0;
+ }
+
+ /*
+ * Set new la_size according to the (still large) ra_size.
+ */
+ *la_size = *ra_size / LOOKAHEAD_RATIO;
+
+ return 1;
+}
+
+static void limit_rala(unsigned long ra_max, unsigned long la_old,
+ unsigned long *ra_size, unsigned long *la_size)
+{
+ unsigned long stream_shift;
+
+ /*
+ * Apply basic upper limits.
+ */
+ if (*ra_size > ra_max)
+ *ra_size = ra_max;
+ if (*la_size > *ra_size)
+ *la_size = *ra_size;
+
+ /*
+ * Make sure stream_shift is not too small.
+ * (So that the next global_shift will not be too small.)
+ */
+ stream_shift = la_old + (*ra_size - *la_size);
+ if (stream_shift < *ra_size / 4)
+ *la_size -= (*ra_size / 4 - stream_shift);
+}
+
+/*
+ * The function estimates two values:
+ * 1. thrashing-threshold for the current stream
+ * It is returned to make the next read-ahead request.
+ * 2. the remained safe space for the current chunk
+ * It will be checked to ensure that the current chunk is safe.
+ *
+ * The computation will be pretty accurate under heavy load, and will vibrate
+ * more on light load(with small global_shift), so the grow speed of ra_size
+ * must be limited, and a moderate large stream_shift must be insured.
+ *
+ * This figure illustrates the formula used in the function:
+ * While the stream reads stream_shift pages inside the chunks,
+ * the chunks are shifted global_shift pages inside inactive_list.
+ *
+ * chunk A chunk B
+ * |<=============== global_shift ================|
+ * +-------------+ +-------------------+ |
+ * | # | | # | inactive_list |
+ * +-------------+ +-------------------+ head |
+ * |---->| |---------->|
+ * | |
+ * +-- stream_shift --+
+ */
+static unsigned long compute_thrashing_threshold(struct file_ra_state *ra,
+ unsigned long *remain)
+{
+ unsigned long global_size;
+ unsigned long global_shift;
+ unsigned long stream_shift;
+ unsigned long ra_size;
+ uint64_t ll;
+
+ global_size = nr_free_inactive_pages_node(numa_node_id());
+ global_shift = node_readahead_aging() - ra->age;
+ global_shift |= 1UL;
+ stream_shift = ra_invoke_interval(ra);
+
+ /* future safe space */
+ ll = (uint64_t) stream_shift * (global_size >> 9) * readahead_ratio * 5;
+ do_div(ll, global_shift);
+ ra_size = ll;
+
+ /* remained safe space */
+ if (global_size > global_shift) {
+ ll = (uint64_t) stream_shift * (global_size - global_shift);
+ do_div(ll, global_shift);
+ *remain = ll;
+ } else
+ *remain = 0;
+
+ ddprintk("compute_thrashing_threshold: "
+ "at %lu ra %lu=%lu*%lu/%lu, remain %lu for %lu\n",
+ ra->readahead_index, ra_size,
+ stream_shift, global_size, global_shift,
+ *remain, ra_lookahead_size(ra));
+
+ return ra_size;
+}
+
+/*
+ * Main function for file_ra_state based read-ahead.
+ */
+static unsigned long
+state_based_readahead(struct address_space *mapping, struct file *filp,
+ struct file_ra_state *ra,
+ struct page *page, pgoff_t index,
+ unsigned long req_size, unsigned long ra_max)
+{
+ unsigned long ra_old, ra_size;
+ unsigned long la_old, la_size;
+ unsigned long remain_space;
+ unsigned long growth_limit;
+
+ la_old = la_size = ra->readahead_index - index;
+ ra_old = ra_readahead_size(ra);
+ ra_size = compute_thrashing_threshold(ra, &remain_space);
+
+ if (page && remain_space <= la_size && la_size > 1) {
+ rescue_pages(page, la_size);
+ return 0;
+ }
+
+ growth_limit = req_size;
+ growth_limit += ra_max / 16;
+ growth_limit += (2 + readahead_ratio / 64) * ra_old;
+ if (growth_limit > ra_max)
+ growth_limit = ra_max;
+
+ if (!adjust_rala(growth_limit, &ra_size, &la_size))
+ return 0;
+
+ limit_rala(growth_limit, la_old, &ra_size, &la_size);
+
+ /* ra_size in its _steady_ state reflects thrashing threshold */
+ if (page && ra_old + ra_old / 8 >= ra_size)
+ update_ra_thrash_bytes(mapping->backing_dev_info, ra_size);
+
+ ra_set_class(ra, RA_CLASS_STATE);
+ ra_set_index(ra, index, ra->readahead_index);
+ ra_set_size(ra, ra_size, la_size);
+
+ return ra_dispatch(ra, mapping, filp);
+}
+
+/*
+ * Page cache context based estimation of read-ahead/look-ahead size/index.
+ *
+ * The logic first looks around to find the start point of next read-ahead,
+ * and then, if necessary, looks backward in the inactive_list to get an
+ * estimation of the thrashing-threshold.
+ *
+ * The estimation theory can be illustrated with figure:
+ *
+ * chunk A chunk B chunk C head
+ *
+ * l01 l11 l12 l21 l22
+ *| |-->|-->| |------>|-->| |------>|
+ *| +-------+ +-----------+ +-------------+ |
+ *| | # | | # | | # | |
+ *| +-------+ +-----------+ +-------------+ |
+ *| |<==============|<===========================|<============================|
+ * L0 L1 L2
+ *
+ * Let f(l) = L be a map from
+ * l: the number of pages read by the stream
+ * to
+ * L: the number of pages pushed into inactive_list in the mean time
+ * then
+ * f(l01) <= L0
+ * f(l11 + l12) = L1
+ * f(l21 + l22) = L2
+ * ...
+ * f(l01 + l11 + ...) <= Sum(L0 + L1 + ...)
+ * <= Length(inactive_list) = f(thrashing-threshold)
+ *
+ * So the count of countinuous history pages left in the inactive_list is always
+ * a lower estimation of the true thrashing-threshold.
+ */
+
+#if PG_active < PG_referenced
+# error unexpected page flags order
+#endif
+
+#define PAGE_REFCNT_0 0
+#define PAGE_REFCNT_1 (1 << PG_referenced)
+#define PAGE_REFCNT_2 (1 << PG_active)
+#define PAGE_REFCNT_3 ((1 << PG_active) | (1 << PG_referenced))
+#define PAGE_REFCNT_MASK PAGE_REFCNT_3
+
+/*
+ * STATUS REFERENCE COUNT TYPE
+ * __ 0 fresh
+ * _R PAGE_REFCNT_1 stale
+ * A_ PAGE_REFCNT_2 disturbed once
+ * AR PAGE_REFCNT_3 disturbed twice
+ *
+ * A/R: Active / Referenced
+ */
+static inline unsigned long page_refcnt(struct page *page)
+{
+ return page->flags & PAGE_REFCNT_MASK;
+}
+
+/*
+ * Now that revisited pages are put into active_list immediately,
+ * we cannot get an accurate estimation of
+ *
+ * len(inactive_list) / speed(leader)
+ *
+ * on the situation of two sequential readers that come close enough:
+ *
+ * chunk 1 chunk 2 chunk 3
+ * ========== =============------- --------------------
+ * follower ^ leader ^
+ *
+ * In this case, using inactive_page_refcnt() in the context based method yields
+ * conservative read-ahead size, while page_refcnt() yields aggressive size.
+ */
+static inline unsigned long inactive_page_refcnt(struct page *page)
+{
+ if (!page || PageActive(page))
+ return 0;
+
+ return page_refcnt(page);
+}
+
+/*
+ * Find past-the-end index of the segment at @index.
+ *
+ * Segment is defined as a full range of cached pages in a file.
+ * (Whereas a chunk refers to a range of cached pages that are brought in
+ * by read-ahead in one shot.)
+ */
+static pgoff_t find_segtail(struct address_space *mapping,
+ pgoff_t index, unsigned long max_scan)
+{
+ pgoff_t ra_index;
+
+ cond_resched();
+ read_lock_irq(&mapping->tree_lock);
+ ra_index = radix_tree_scan_hole(&mapping->page_tree, index, max_scan);
+#ifdef DEBUG_READAHEAD_RADIXTREE
+ BUG_ON(!__probe_page(mapping, index));
+ WARN_ON(ra_index < index);
+ if (ra_index != index && !__probe_page(mapping, ra_index - 1))
+ printk(KERN_ERR "radix_tree_scan_hole(index=%lu ra_index=%lu "
+ "max_scan=%lu nrpages=%lu) fooled!\n",
+ index, ra_index, max_scan, mapping->nrpages);
+ if (ra_index != ~0UL && ra_index - index < max_scan)
+ WARN_ON(__probe_page(mapping, ra_index));
+#endif
+ read_unlock_irq(&mapping->tree_lock);
+
+ if (ra_index <= index + max_scan)
+ return ra_index;
+ else
+ return 0;
+}
+
+/*
+ * Find past-the-end index of the segment before @index.
+ */
+static pgoff_t find_segtail_backward(struct address_space *mapping,
+ pgoff_t index, unsigned long max_scan)
+{
+ pgoff_t origin = index;
+
+ if (max_scan > index)
+ max_scan = index;
+
+ /*
+ * Poor man's radix_tree_scan_data_backward() implementation.
+ * Acceptable because max_scan won't be large.
+ */
+ read_lock_irq(&mapping->tree_lock);
+ for (; origin - index < max_scan;)
+ if (__probe_page(mapping, --index)) {
+ read_unlock_irq(&mapping->tree_lock);
+ return index + 1;
+ }
+ read_unlock_irq(&mapping->tree_lock);
+
+ return 0;
+}
+
+/*
+ * Count/estimate cache hits in range [first_index, last_index].
+ * The estimation is simple and optimistic.
+ */
+#define CACHE_HIT_HASH_KEY 29 /* some prime number */
+static int count_cache_hit(struct address_space *mapping,
+ pgoff_t first_index, pgoff_t last_index)
+{
+ struct page *page;
+ int size = last_index - first_index + 1;
+ int count = 0;
+ int i;
+
+ /*
+ * The first page may well is chunk head and has been accessed,
+ * so it is index 0 that makes the estimation optimistic. This
+ * behavior guarantees a readahead when (size < ra_max) and
+ * (readahead_hit_rate >= 16).
+ */
+ for (i = 0; i < 16;) {
+ page = radix_tree_lookup(&mapping->page_tree, first_index +
+ size * ((i++ * CACHE_HIT_HASH_KEY) & 15) / 16);
+ if (inactive_page_refcnt(page) >= PAGE_REFCNT_1 && ++count >= 2)
+ break;
+ }
+
+ return size * count / i;
+}
+
+/*
+ * Look back and check history pages to estimate thrashing-threshold.
+ */
+static unsigned long query_page_cache_segment(struct address_space *mapping,
+ struct file_ra_state *ra,
+ unsigned long *remain, pgoff_t offset,
+ unsigned long ra_min, unsigned long ra_max)
+{
+ pgoff_t index;
+ unsigned long count;
+ unsigned long nr_lookback;
+
+ /*
+ * Scan backward and check the near @ra_max pages.
+ * The count here determines ra_size.
+ */
+ cond_resched();
+ read_lock_irq(&mapping->tree_lock);
+ index = radix_tree_scan_hole_backward(&mapping->page_tree,
+ offset - 1, ra_max);
+#ifdef DEBUG_READAHEAD_RADIXTREE
+ WARN_ON(index > offset - 1);
+ if (index != offset - 1)
+ WARN_ON(!__probe_page(mapping, index + 1));
+ if (index && offset - 1 - index < ra_max)
+ WARN_ON(__probe_page(mapping, index));
+#endif
+
+ *remain = (offset - 1) - index;
+
+ if (offset == ra->readahead_index && ra_cache_hit_ok(ra))
+ count = *remain;
+ else if (count_cache_hit(mapping, index + 1, offset) *
+ readahead_hit_rate >= *remain)
+ count = *remain;
+ else
+ count = ra_min;
+
+ /*
+ * Unnecessary to count more?
+ */
+ if (count < ra_max)
+ goto out_unlock;
+
+ if (unlikely(ra->flags & RA_FLAG_NO_LOOKAHEAD))
+ goto out_unlock;
+
+ /*
+ * Check the far pages coarsely.
+ * The enlarged count here helps increase la_size.
+ */
+ nr_lookback = ra_max * (LOOKAHEAD_RATIO + 1) *
+ 100 / (readahead_ratio | 1);
+
+ for (count += ra_max; count < nr_lookback; count += ra_max)
+ if (!__probe_page(mapping, offset - count))
+ break;
+
+out_unlock:
+ read_unlock_irq(&mapping->tree_lock);
+
+ /*
+ * For sequential read that extends from index 0, the counted value
+ * may well be far under the true threshold, so return it unmodified
+ * for further processing in adjust_rala_aggressive().
+ */
+ if (count >= offset)
+ count = offset;
+ else
+ count = max(ra_min, count * readahead_ratio / 100);
+
+ ddprintk("query_page_cache_segment: "
+ "ino=%lu, idx=%lu, count=%lu, remain=%lu\n",
+ mapping->host->i_ino, offset, count, *remain);
+
+ return count;
+}
+
+/*
+ * Determine the request parameters for context based read-ahead that extends
+ * from start of file.
+ *
+ * One major weakness of stateless method is the slow scaling up of ra_size.
+ * The logic tries to make up for this in the important case of sequential
+ * reads that extend from start of file. In this case, the ra_size is not
+ * chosen to make the whole next chunk safe (as in normal ones). Only part of
+ * which is safe: the tailing look-ahead part is 'unsafe'. However it will be
+ * safeguarded by rescue_pages() when the previous chunks are lost.
+ */
+static int adjust_rala_aggressive(unsigned long ra_max,
+ unsigned long *ra_size, unsigned long *la_size)
+{
+ pgoff_t index = *ra_size;
+
+ *ra_size -= min(*ra_size, *la_size);
+ *ra_size = *ra_size * readahead_ratio / 100;
+ *la_size = index * readahead_ratio / 100;
+ *ra_size += *la_size;
+
+ return 1;
+}
+
+/*
+ * Main function for page context based read-ahead.
+ *
+ * RETURN VALUE HINT
+ * 1 @ra contains a valid ra-request, please submit it
+ * 0 no seq-pattern discovered, please try the next method
+ * -1 please don't do _any_ readahead
+ */
+static int
+try_context_based_readahead(struct address_space *mapping,
+ struct file_ra_state *ra, struct page *prev_page,
+ struct page *page, pgoff_t index,
+ unsigned long ra_min, unsigned long ra_max)
+{
+ pgoff_t ra_index;
+ unsigned long ra_size;
+ unsigned long la_size;
+ unsigned long remain_pages;
+
+ /* Where to start read-ahead?
+ * NFSv3 daemons may process adjacent requests in parallel,
+ * leading to many locally disordered, globally sequential reads.
+ * So do not require nearby history pages to be present or accessed.
+ */
+ if (page) {
+ ra_index = find_segtail(mapping, index, ra_max * 5 / 4);
+ if (!ra_index)
+ return -1;
+ } else if (prev_page || probe_page(mapping, index - 1)) {
+ ra_index = index;
+ } else if (readahead_hit_rate > 1) {
+ ra_index = find_segtail_backward(mapping, index,
+ readahead_hit_rate + ra_min);
+ if (!ra_index)
+ return 0;
+ ra_min += 2 * (index - ra_index);
+ index = ra_index; /* pretend the request starts here */
+ } else
+ return 0;
+
+ ra_size = query_page_cache_segment(mapping, ra, &remain_pages,
+ index, ra_min, ra_max);
+
+ la_size = ra_index - index;
+ if (page && remain_pages <= la_size &&
+ remain_pages < index && la_size > 1) {
+ rescue_pages(page, la_size);
+ return -1;
+ }
+
+ if (ra_size == index) {
+ if (!adjust_rala_aggressive(ra_max, &ra_size, &la_size))
+ return -1;
+ ra_set_class(ra, RA_CLASS_CONTEXT_AGGRESSIVE);
+ } else {
+ if (!adjust_rala(ra_max, &ra_size, &la_size))
+ return -1;
+ ra_set_class(ra, RA_CLASS_CONTEXT);
+ }
+
+ limit_rala(ra_max, ra_index - index, &ra_size, &la_size);
+
+ ra_set_index(ra, index, ra_index);
+ ra_set_size(ra, ra_size, la_size);
+
+ return 1;
+}
+
+/*
+ * Read-ahead on start of file.
+ *
+ * We want to be as aggressive as possible, _and_
+ * - do not ruin the hit rate for file-head-peekers
+ * - do not lead to thrashing for memory tight systems
+ */
+static unsigned long
+initial_readahead(struct address_space *mapping, struct file *filp,
+ struct file_ra_state *ra, unsigned long req_size)
+{
+ struct backing_dev_info *bdi = mapping->backing_dev_info;
+ unsigned long thrash_pages = bdi->ra_thrash_bytes >> PAGE_CACHE_SHIFT;
+ unsigned long expect_pages = bdi->ra_expect_bytes >> PAGE_CACHE_SHIFT;
+ unsigned long ra_size;
+ unsigned long la_size;
+
+ ra_size = req_size;
+
+ /* be aggressive if the system tends to read more */
+ if (ra_size < expect_pages)
+ ra_size = expect_pages;
+
+ /* no read-ahead thrashing */
+ if (ra_size > thrash_pages)
+ ra_size = thrash_pages;
+
+ /* do look-ahead on large(>= 32KB) read-ahead */
+ la_size = ra_size / LOOKAHEAD_RATIO;
+
+ ra_set_class(ra, RA_CLASS_INITIAL);
+ ra_set_index(ra, 0, 0);
+ ra_set_size(ra, ra_size, la_size);
+
+ return ra_dispatch(ra, mapping, filp);
+}
+
+/*
+ * Backward prefetching.
+ *
+ * No look-ahead and thrashing safety guard: should be unnecessary.
+ *
+ * Important for certain scientific arenas(i.e. structural analysis).
+ */
+static int
+try_read_backward(struct file_ra_state *ra, pgoff_t begin_index,
+ unsigned long ra_size, unsigned long ra_max)
+{
+ pgoff_t end_index;
+
+ /* Are we reading backward? */
+ if (begin_index > ra->prev_page)
+ return 0;
+
+ if ((ra->flags & RA_CLASS_MASK) == RA_CLASS_BACKWARD &&
+ ra_has_index(ra, ra->prev_page)) {
+ ra_size += 2 * ra->hit0;
+ end_index = ra->la_index;
+ } else {
+ ra_size += ra_size + ra_size * (readahead_hit_rate - 1) / 2;
+ end_index = ra->prev_page;
+ }
+
+ if (ra_size > ra_max)
+ ra_size = ra_max;
+
+ /* Read traces close enough to be covered by the prefetching? */
+ if (end_index > begin_index + ra_size)
+ return 0;
+
+ begin_index = end_index - ra_size;
+
+ ra_set_class(ra, RA_CLASS_BACKWARD);
+ ra_set_index(ra, begin_index, begin_index);
+ ra_set_size(ra, ra_size, 0);
+
+ return 1;
+}
+
+/*
+ * If there is a previous sequential read, it is likely to be another
+ * sequential read at the new position.
+ *
+ * i.e. detect the following sequences:
+ * seek(), 5*read(); seek(), 6*read(); seek(), 4*read(); ...
+ *
+ * Databases are known to have this seek-and-read-N-pages pattern.
+ */
+static int
+try_readahead_on_seek(struct file_ra_state *ra, pgoff_t index,
+ unsigned long ra_size, unsigned long ra_max)
+{
+ unsigned long hit0 = ra->hit0;
+ unsigned long hit1 = ra->hit1 + hit0;
+ unsigned long hit2 = ra->hit2;
+ unsigned long hit3 = ra->hit3;
+
+ /* There's a previous read-ahead request? */
+ if (!ra_has_index(ra, ra->prev_page))
+ return 0;
+
+ /* The previous read-ahead sequences have similiar sizes? */
+ if (!(ra_size < hit1 && hit1 > hit2 / 2 &&
+ hit2 > hit3 / 2 &&
+ hit3 > hit1 / 2))
+ return 0;
+
+ hit1 = max(hit1, hit2);
+
+ /* Follow the same prefetching direction. */
+ if ((ra->flags & RA_CLASS_MASK) == RA_CLASS_BACKWARD)
+ index = ((index > hit1 - ra_size) ? index - hit1 + ra_size : 0);
+
+ ra_size = min(hit1, ra_max);
+
+ ra_set_class(ra, RA_CLASS_SEEK);
+ ra_set_index(ra, index, index);
+ ra_set_size(ra, ra_size, 0);
+
+ return 1;
+}
+
+/*
+ * Readahead thrashing recovery.
+ */
+static unsigned long
+thrashing_recovery_readahead(struct address_space *mapping,
+ struct file *filp, struct file_ra_state *ra,
+ pgoff_t index, unsigned long ra_max)
+{
+ unsigned long ra_size;
+
+ if (probe_page(mapping, index - 1))
+ ra_account(ra, RA_EVENT_READAHEAD_MUTILATE,
+ ra->readahead_index - index);
+ ra_account(ra, RA_EVENT_READAHEAD_THRASHING,
+ ra->readahead_index - index);
+
+ /*
+ * Some thrashing occur in (ra_index, la_index], in which case the
+ * old read-ahead chunk is lost soon after the new one is allocated.
+ * Ensure that we recover all needed pages in the old chunk.
+ */
+ if (index < ra->ra_index)
+ ra_size = ra->ra_index - index;
+ else {
+ /* After thrashing, we know the exact thrashing-threshold. */
+ ra_size = ra->hit0;
+ update_ra_thrash_bytes(mapping->backing_dev_info, ra_size);
+
+ /* And we'd better be a bit conservative. */
+ ra_size = ra_size * 3 / 4;
+ }
+
+ if (ra_size > ra_max)
+ ra_size = ra_max;
+
+ ra_set_class(ra, RA_CLASS_THRASHING);
+ ra_set_index(ra, index, index);
+ ra_set_size(ra, ra_size, ra_size / LOOKAHEAD_RATIO);
+
+ return ra_dispatch(ra, mapping, filp);
+}
+
+/*
+ * ra_min is mainly determined by the size of cache memory. Reasonable?
+ *
+ * Table of concrete numbers for 4KB page size:
+ * inactive + free (MB): 4 8 16 32 64 128 256 512 1024
+ * ra_min (KB): 16 16 16 16 20 24 32 48 64
+ */
+static inline void get_readahead_bounds(struct file_ra_state *ra,
+ unsigned long *ra_min,
+ unsigned long *ra_max)
+{
+ unsigned long pages;
+
+ pages = max_sane_readahead((1<<30) / PAGE_CACHE_SIZE);
+ *ra_max = min(min(pages, 0xFFFFUL), ra->ra_pages);
+ *ra_min = min(min(MIN_RA_PAGES + (pages >> 13),
+ (128*1024) / PAGE_CACHE_SIZE), *ra_max / 2);
+}
+
+/**
+ * page_cache_readahead_adaptive - thrashing safe adaptive read-ahead
+ * @mapping, @ra, @filp: the same as page_cache_readahead()
+ * @prev_page: the page at @index-1, may be NULL to let the function find it
+ * @page: the page at @index, or NULL if non-present
+ * @begin_index, @index, @end_index: offsets into @mapping
+ * [@begin_index, @end_index) is the read the caller is performing
+ * @index indicates the page to be read now
+ *
+ * page_cache_readahead_adaptive() is the entry point of the adaptive
+ * read-ahead logic. It tries a set of methods in turn to determine the
+ * appropriate readahead action and submits the readahead I/O.
+ *
+ * The caller is expected to point ra->prev_page to the previously accessed
+ * page, and to call it on two conditions:
+ * 1. @page == NULL
+ * A cache miss happened, some pages have to be read in
+ * 2. @page != NULL && PageReadahead(@page)
+ * A look-ahead mark encountered, this is set by a previous read-ahead
+ * invocation to instruct the caller to give the function a chance to
+ * check up and do next read-ahead in advance.
+ */
+unsigned long
+page_cache_readahead_adaptive(struct address_space *mapping,
+ struct file_ra_state *ra, struct file *filp,
+ struct page *prev_page, struct page *page,
+ pgoff_t begin_index, pgoff_t index, pgoff_t end_index)
+{
+ unsigned long size;
+ unsigned long ra_min;
+ unsigned long ra_max;
+ int ret;
+
+ might_sleep();
+
+ if (page) {
+ if(!TestClearPageReadahead(page))
+ return 0;
+ if (bdi_read_congested(mapping->backing_dev_info)) {
+ ra_account(ra, RA_EVENT_IO_CONGESTION,
+ end_index - index);
+ return 0;
+ }
+ if (laptop_mode && laptop_spinned_down()) {
+ if (!renew_lookahead(mapping, ra, index,
+ index + LAPTOP_POLL_INTERVAL))
+ return 0;
+ }
+ }
+
+ if (page)
+ ra_account(ra, RA_EVENT_LOOKAHEAD_HIT,
+ ra->readahead_index - ra->lookahead_index);
+ else if (index)
+ ra_account(ra, RA_EVENT_CACHE_MISS, end_index - begin_index);
+
+ size = end_index - index;
+ get_readahead_bounds(ra, &ra_min, &ra_max);
+
+ /* readahead disabled? */
+ if (unlikely(!ra_max || !readahead_ratio)) {
+ size = max_sane_readahead(size);
+ goto readit;
+ }
+
+ /*
+ * Start of file.
+ */
+ if (index == 0)
+ return initial_readahead(mapping, filp, ra, size);
+
+ /*
+ * State based sequential read-ahead.
+ */
+ if (!debug_option(disable_stateful_method) &&
+ index == ra->lookahead_index && ra_cache_hit_ok(ra))
+ return state_based_readahead(mapping, filp, ra, page,
+ index, size, ra_max);
+
+ /*
+ * Recover from possible thrashing.
+ */
+ if (!page && index == ra->prev_page + 1 && ra_has_index(ra, index))
+ return thrashing_recovery_readahead(mapping, filp, ra,
+ index, ra_max);
+
+ /*
+ * Backward read-ahead.
+ */
+ if (!page && begin_index == index &&
+ try_read_backward(ra, index, size, ra_max))
+ return ra_dispatch(ra, mapping, filp);
+
+ /*
+ * Context based sequential read-ahead.
+ */
+ ret = try_context_based_readahead(mapping, ra, prev_page, page,
+ index, ra_min, ra_max);
+ if (ret > 0)
+ return ra_dispatch(ra, mapping, filp);
+ if (ret < 0)
+ return 0;
+
+ /* No action on look ahead time? */
+ if (page) {
+ ra_account(ra, RA_EVENT_LOOKAHEAD_NOACTION,
+ ra->readahead_index - index);
+ return 0;
+ }
+
+ /*
+ * Random read that follows a sequential one.
+ */
+ if (try_readahead_on_seek(ra, index, size, ra_max))
+ return ra_dispatch(ra, mapping, filp);
+
+ /*
+ * Random read.
+ */
+ if (size > ra_max)
+ size = ra_max;
+
+readit:
+ size = __do_page_cache_readahead(mapping, filp, index, size, 0);
+
+ ra_account(ra, RA_EVENT_RANDOM_READ, size);
+ dprintk("random_read(ino=%lu, pages=%lu, index=%lu-%lu-%lu) = %lu\n",
+ mapping->host->i_ino, mapping->nrpages,
+ begin_index, index, end_index, size);
+
+ return size;
+}
+
+/**
+ * readahead_cache_hit - adaptive read-ahead feedback function
+ * @ra: file_ra_state which holds the readahead state
+ * @page: the page just accessed
+ *
+ * readahead_cache_hit() is the feedback route of the adaptive read-ahead
+ * logic. It must be called on every access on the read-ahead pages.
+ */
+void readahead_cache_hit(struct file_ra_state *ra, struct page *page)
+{
+ if (PageActive(page) || PageReferenced(page))
+ return;
+
+ if (!PageUptodate(page))
+ ra_account(ra, RA_EVENT_IO_BLOCK, 1);
+
+ if (!ra_has_index(ra, page->index))
+ return;
+
+ ra->hit0++;
+
+ if (page->index >= ra->ra_index)
+ ra_account(ra, RA_EVENT_READAHEAD_HIT, 1);
+ else
+ ra_account(ra, RA_EVENT_READAHEAD_HIT, -1);
+}
+
+/*
+ * 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 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; /* supposed to be small */
+ unsigned long pgrahit = file->f_ra.hit0;
+ unsigned long pgcached = mapping->nrpages;
+ unsigned long pgaccess;
+
+ if (!pos) /* pread */
+ return;
+
+ if (pgcached > bdi->ra_pages0) /* excessive reads */
+ return;
+
+ pgaccess = max(pgrahit, 1 + pos / PAGE_CACHE_SIZE);
+ 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 */
+
+/*
+ * Read-ahead events accounting.
+ */
+#ifdef CONFIG_DEBUG_READAHEAD
+
+#include <linux/init.h>
+#include <linux/jiffies.h>
+#include <linux/debugfs.h>
+#include <linux/seq_file.h>
+
+static const char * const ra_class_name[] = {
+ "total",
+ "initial",
+ "state",
+ "context",
+ "contexta",
+ "backward",
+ "onthrash",
+ "onseek",
+ "none"
+};
+
+static const char * const ra_event_name[] = {
+ "cache_miss",
+ "random_read",
+ "io_congestion",
+ "io_cache_hit",
+ "io_block",
+ "readahead",
+ "readahead_hit",
+ "lookahead",
+ "lookahead_hit",
+ "lookahead_ignore",
+ "readahead_mmap",
+ "readahead_eof",
+ "readahead_shrink",
+ "readahead_thrash",
+ "readahead_mutilt",
+ "readahead_rescue"
+};
+
+static unsigned long ra_events[RA_CLASS_COUNT][RA_EVENT_COUNT][2];
+
+static void ra_account(struct file_ra_state *ra, enum ra_event e, int pages)
+{
+ enum ra_class c;
+
+ if (!debug_level)
+ return;
+
+ if (e == RA_EVENT_READAHEAD_HIT && pages < 0) {
+ c = ra_class_old(ra);
+ pages = -pages;
+ } else if (ra)
+ c = ra_class_new(ra);
+ else
+ c = RA_CLASS_NONE;
+
+ if (!c)
+ c = RA_CLASS_NONE;
+
+ ra_events[c][e][0] += 1;
+ ra_events[c][e][1] += pages;
+
+ if (e == RA_EVENT_READAHEAD)
+ ra_events[c][RA_EVENT_READAHEAD_CUBE][1] += pages * pages;
+}
+
+static int ra_events_show(struct seq_file *s, void *_)
+{
+ int i;
+ int c;
+ int e;
+ static const char event_fmt[] = "%-16s";
+ static const char class_fmt[] = "%10s";
+ static const char item_fmt[] = "%10lu";
+ static const char percent_format[] = "%9lu%%";
+ static const char * const table_name[] = {
+ "[table requests]",
+ "[table pages]",
+ "[table summary]"};
+
+ for (i = 0; i <= 1; i++) {
+ for (e = 0; e < RA_EVENT_COUNT; e++) {
+ ra_events[RA_CLASS_ALL][e][i] = 0;
+ for (c = RA_CLASS_INITIAL; c < RA_CLASS_NONE; c++)
+ ra_events[RA_CLASS_ALL][e][i] += ra_events[c][e][i];
+ }
+
+ seq_printf(s, event_fmt, table_name[i]);
+ for (c = 0; c < RA_CLASS_COUNT; c++)
+ seq_printf(s, class_fmt, ra_class_name[c]);
+ seq_puts(s, "\n");
+
+ for (e = 0; e < RA_EVENT_COUNT; e++) {
+ if (e == RA_EVENT_READAHEAD_CUBE)
+ continue;
+ if (e == RA_EVENT_READAHEAD_HIT && i == 0)
+ continue;
+ if (e == RA_EVENT_IO_BLOCK && i == 1)
+ continue;
+
+ seq_printf(s, event_fmt, ra_event_name[e]);
+ for (c = 0; c < RA_CLASS_COUNT; c++)
+ seq_printf(s, item_fmt, ra_events[c][e][i]);
+ seq_puts(s, "\n");
+ }
+ seq_puts(s, "\n");
+ }
+
+ seq_printf(s, event_fmt, table_name[2]);
+ for (c = 0; c < RA_CLASS_COUNT; c++)
+ seq_printf(s, class_fmt, ra_class_name[c]);
+ seq_puts(s, "\n");
+
+ seq_printf(s, event_fmt, "random_rate");
+ for (c = 0; c < RA_CLASS_COUNT; c++)
+ seq_printf(s, percent_format,
+ (ra_events[c][RA_EVENT_RANDOM_READ][0] * 100) /
+ ((ra_events[c][RA_EVENT_RANDOM_READ][0] +
+ ra_events[c][RA_EVENT_READAHEAD][0]) | 1));
+ seq_puts(s, "\n");
+
+ seq_printf(s, event_fmt, "ra_hit_rate");
+ for (c = 0; c < RA_CLASS_COUNT; c++)
+ seq_printf(s, percent_format,
+ (ra_events[c][RA_EVENT_READAHEAD_HIT][1] * 100) /
+ (ra_events[c][RA_EVENT_READAHEAD][1] | 1));
+ seq_puts(s, "\n");
+
+ seq_printf(s, event_fmt, "la_hit_rate");
+ for (c = 0; c < RA_CLASS_COUNT; c++)
+ seq_printf(s, percent_format,
+ (ra_events[c][RA_EVENT_LOOKAHEAD_HIT][0] * 100) /
+ (ra_events[c][RA_EVENT_LOOKAHEAD][0] | 1));
+ seq_puts(s, "\n");
+
+ seq_printf(s, event_fmt, "var_ra_size");
+ for (c = 0; c < RA_CLASS_COUNT; c++)
+ seq_printf(s, item_fmt,
+ (ra_events[c][RA_EVENT_READAHEAD_CUBE][1] -
+ ra_events[c][RA_EVENT_READAHEAD][1] *
+ (ra_events[c][RA_EVENT_READAHEAD][1] /
+ (ra_events[c][RA_EVENT_READAHEAD][0] | 1))) /
+ (ra_events[c][RA_EVENT_READAHEAD][0] | 1));
+ seq_puts(s, "\n");
+
+ seq_printf(s, event_fmt, "avg_ra_size");
+ for (c = 0; c < RA_CLASS_COUNT; c++)
+ seq_printf(s, item_fmt,
+ (ra_events[c][RA_EVENT_READAHEAD][1] +
+ ra_events[c][RA_EVENT_READAHEAD][0] / 2) /
+ (ra_events[c][RA_EVENT_READAHEAD][0] | 1));
+ seq_puts(s, "\n");
+
+ seq_printf(s, event_fmt, "avg_la_size");
+ for (c = 0; c < RA_CLASS_COUNT; c++)
+ seq_printf(s, item_fmt,
+ (ra_events[c][RA_EVENT_LOOKAHEAD][1] +
+ ra_events[c][RA_EVENT_LOOKAHEAD][0] / 2) /
+ (ra_events[c][RA_EVENT_LOOKAHEAD][0] | 1));
+ seq_puts(s, "\n");
+
+ return 0;
+}
+
+static int ra_events_open(struct inode *inode, struct file *file)
+{
+ return single_open(file, ra_events_show, NULL);
+}
+
+static ssize_t ra_events_write(struct file *file, const char __user *buf,
+ size_t size, loff_t *offset)
+{
+ memset(ra_events, 0, sizeof(ra_events));
+ return 1;
+}
+
+struct file_operations ra_events_fops = {
+ .owner = THIS_MODULE,
+ .open = ra_events_open,
+ .write = ra_events_write,
+ .read = seq_read,
+ .llseek = seq_lseek,
+ .release = single_release,
+};
+
+#define READAHEAD_DEBUGFS_ENTRY_U32(var) \
+ debugfs_create_u32(__stringify(var), 0644, root, &var)
+
+#define READAHEAD_DEBUGFS_ENTRY_BOOL(var) \
+ debugfs_create_bool(__stringify(var), 0644, root, &var)
+
+static int __init readahead_init(void)
+{
+ struct dentry *root;
+
+ root = debugfs_create_dir("readahead", NULL);
+
+ debugfs_create_file("events", 0644, root, NULL, &ra_events_fops);
+
+ READAHEAD_DEBUGFS_ENTRY_U32(initial_ra_hit);
+ READAHEAD_DEBUGFS_ENTRY_U32(initial_ra_miss);
+
+ READAHEAD_DEBUGFS_ENTRY_U32(debug_level);
+ READAHEAD_DEBUGFS_ENTRY_BOOL(disable_stateful_method);
+
+ return 0;
+}
+
+module_init(readahead_init)
+
+#endif /* CONFIG_DEBUG_READAHEAD */
--- linux-2.6.17-rc5.orig/mm/swap.c
+++ linux-2.6.17-rc5/mm/swap.c
@@ -127,6 +127,8 @@ void fastcall mark_page_accessed(struct
ClearPageReferenced(page);
} else if (!PageReferenced(page)) {
SetPageReferenced(page);
+ if (PageLRU(page))
+ inc_readahead_aging();
}
}

--- linux-2.6.17-rc5.orig/mm/vmscan.c
+++ linux-2.6.17-rc5/mm/vmscan.c
@@ -439,6 +439,9 @@ static unsigned long shrink_page_list(st
if (PageWriteback(page))
goto keep_locked;

+ if (!PageReferenced(page))
+ inc_readahead_aging();
+
referenced = page_referenced(page, 1);
/* In active use or really unfreeable? Activate it. */
if (referenced && page_mapping_inuse(page))
@@ -637,6 +640,7 @@ static unsigned long shrink_inactive_lis
&page_list, &nr_scan);
zone->nr_inactive -= nr_taken;
zone->pages_scanned += nr_scan;
+ zone->aging_total += nr_scan;
spin_unlock_irq(&zone->lru_lock);

nr_scanned += nr_scan;