* [PATCH 00/12] Adaptive read-ahead V10
@ 2005-12-16 13:07 Wu Fengguang
2005-12-16 13:07 ` [PATCH 01/12] radixtree: look-aside cache Wu Fengguang
` (11 more replies)
0 siblings, 12 replies; 15+ messages in thread
From: Wu Fengguang @ 2005-12-16 13:07 UTC (permalink / raw)
To: linux-kernel; +Cc: Andrew Morton
The current read-ahead logic uses an inflexible algorithm with 128KB
VM_MAX_READAHEAD. Less memory leads to thrashing, more memory helps no
throughput. The new logic is simply safer and faster. It makes sure
every single read-ahead request is safe for the current load. Memory
tight systems are expected to benefit a lot: no thrashing any more.
It can also help boost I/O throughput for large memory systems, for
VM_MAX_READAHEAD now defaults to 1MB. The value is no longer tightly
coupled with the thrashing problem, and therefore constrainted by it.
Changelog
=========
V10 2005-12-16
- remove delayed page activation
- remove live page protection
- revert mmap readaround to old behavior
- default to original readahead logic
- default to original readahead size
- merge comment fixes from Andreas Mohr
- merge radixtree cleanups from Christoph Lameter
- reduce sizeof(struct file_ra_state) by unnamed union
- stateful method cleanups
- account other read-ahead paths
V9 2005-12-3
- standalone mmap read-around code, a little more smart and tunable
- make stateful method sensible of request size
- decouple readahead_ratio from live pages protection
- let readahead_ratio contribute to ra_size grow speed in stateful method
- account variance of ra_size
V8 2005-11-25
- balance zone aging only in page relaim paths and do it right
- do the aging of slabs in the same way as zones
- add debug code to dump the detailed page reclaim steps
- undo exposing of struct radix_tree_node and uninline related functions
- work better with nfsd
- generalize accelerated context based read-ahead
- account smooth read-ahead aging based on page referenced/activate bits
- avoid divide error in compute_thrashing_threshold()
- more low lantency efforts
- update some comments
- rebase debug actions on debugfs entries instead of magic readahead_ratio values
V7 2005-11-09
- new tunable parameters: readahead_hit_rate/readahead_live_chunk
- support sparse sequential accesses
- delay look-ahead if drive is spinned down in laptop mode
- disable look-ahead for loopback file
- make mandatory thrashing protection more simple and robust
- attempt to improve responsiveness on large read-ahead size
V6 2005-11-01
- cancel look-ahead in laptop mode
- increase read-ahead limit to 0xFFFF pages
V5 2005-10-28
- rewrite context based method to make it clean and robust
- improved accuracy of stateful thrashing threshold estimation
- make page aging equal to the number of code pages scanned
- sort out the thrashing protection logic
- enhanced debug/accounting facilities
V4 2005-10-15
- detect and save live chunks on page reclaim
- support database workload
- support reading backward
- radix tree lookup look-aside cache
V3 2005-10-06
- major code reorganization and documention
- stateful estimation of thrashing-threshold
- context method with accelerated grow up phase
- adaptive look-ahead
- early detection and rescue of pages in danger
- statitics data collection
- synchronized page aging between zones
V2 2005-09-15
- delayed page activation
- look-ahead: towards pipelined read-ahead
V1 2005-09-13
Initial release which features:
o stateless (for now)
o adapts to available memory / read speed
o free of thrashing (in theory)
And handles:
o large number of slow streams (FTP server)
o open/read/close access patterns (NFS server)
o multiple interleaved, sequential streams in one file
(multithread / multimedia / database)
Thanks,
Wu Fengguang
--
Dept. Automation University of Science and Technology of China
^ permalink raw reply [flat|nested] 15+ messages in thread
* [PATCH 01/12] radixtree: look-aside cache
2005-12-16 13:07 [PATCH 00/12] Adaptive read-ahead V10 Wu Fengguang
@ 2005-12-16 13:07 ` Wu Fengguang
2005-12-16 13:07 ` [PATCH 02/12] readahead: some preparation Wu Fengguang
` (10 subsequent siblings)
11 siblings, 0 replies; 15+ messages in thread
From: Wu Fengguang @ 2005-12-16 13:07 UTC (permalink / raw)
To: linux-kernel; +Cc: Andrew Morton, Nick Piggin, Christoph Lameter, Wu Fengguang
[-- Attachment #1: radixtree-lookaside-cache.patch --]
[-- Type: text/plain, Size: 12280 bytes --]
This introduces a set of lookup functions to radix tree for the read-ahead
logic. Other access patterns with high locality may also benefit from them.
- radix_tree_lookup_node(root, index, level)
Perform partial lookup, return the @level'th parent of the slot at
@index.
- radix_tree_cache_xxx()
Init/Query the cache.
- radix_tree_cache_lookup(root, cache, index)
Perform lookup with the aid of a look-aside cache.
For sequential scans, it has a time complexity of 64*O(1) + 1*O(logn).
Typical usage:
void func() {
+ struct radix_tree_cache cache;
+
+ radix_tree_cache_init(&cache);
read_lock_irq(&mapping->tree_lock);
for(;;) {
- page = radix_tree_lookup(&mapping->page_tree, index);
+ page = radix_tree_cache_lookup(&mapping->page_tree, &cache, index);
}
read_unlock_irq(&mapping->tree_lock);
}
- radix_tree_lookup_head(root, index, max_scan)
- radix_tree_lookup_tail(root, index, max_scan)
Assume [head, tail) to be a segment with continuous pages. The two
functions search for the head and tail index of the segment at @index.
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Wu Fengguang <wfg@mail.ustc.edu.cn>
---
include/linux/radix-tree.h | 80 ++++++++++++++++-
lib/radix-tree.c | 208 +++++++++++++++++++++++++++++++++++++++------
2 files changed, 259 insertions(+), 29 deletions(-)
--- linux.orig/include/linux/radix-tree.h
+++ linux/include/linux/radix-tree.h
@@ -23,12 +23,24 @@
#include <linux/preempt.h>
#include <linux/types.h>
+#define RADIX_TREE_MAP_SHIFT 6
+#define RADIX_TREE_MAP_SIZE (1UL << RADIX_TREE_MAP_SHIFT)
+#define RADIX_TREE_MAP_MASK (RADIX_TREE_MAP_SIZE-1)
+
struct radix_tree_root {
unsigned int height;
gfp_t gfp_mask;
struct radix_tree_node *rnode;
};
+/*
+ * Support access patterns with strong locality.
+ */
+struct radix_tree_cache {
+ unsigned long first_index;
+ struct radix_tree_node *tree_node;
+};
+
#define RADIX_TREE_INIT(mask) { \
.height = 0, \
.gfp_mask = (mask), \
@@ -46,9 +58,18 @@ do { \
} while (0)
int radix_tree_insert(struct radix_tree_root *, unsigned long, void *);
-void *radix_tree_lookup(struct radix_tree_root *, unsigned long);
-void **radix_tree_lookup_slot(struct radix_tree_root *, unsigned long);
+void *radix_tree_lookup_node(struct radix_tree_root *, unsigned long,
+ unsigned int);
+void **radix_tree_lookup_slot(struct radix_tree_root *root, unsigned long);
void *radix_tree_delete(struct radix_tree_root *, unsigned long);
+int radix_tree_cache_count(struct radix_tree_cache *cache);
+void *radix_tree_cache_lookup_node(struct radix_tree_root *root,
+ struct radix_tree_cache *cache,
+ unsigned long index, unsigned int level);
+unsigned long radix_tree_lookup_head(struct radix_tree_root *root,
+ unsigned long index, unsigned int max_scan);
+unsigned long radix_tree_lookup_tail(struct radix_tree_root *root,
+ unsigned long index, unsigned int max_scan);
unsigned int
radix_tree_gang_lookup(struct radix_tree_root *root, void **results,
unsigned long first_index, unsigned int max_items);
@@ -70,4 +91,59 @@ static inline void radix_tree_preload_en
preempt_enable();
}
+/**
+ * radix_tree_lookup - perform lookup operation on a radix tree
+ * @root: radix tree root
+ * @index: index key
+ *
+ * Lookup the item at the position @index in the radix tree @root.
+ */
+static inline void *radix_tree_lookup(struct radix_tree_root *root,
+ unsigned long index)
+{
+ return radix_tree_lookup_node(root, index, 0);
+}
+
+/**
+ * radix_tree_cache_init - init the cache
+ * @cache: look-aside cache
+ *
+ * Init the @cache.
+ */
+static inline void radix_tree_cache_init(struct radix_tree_cache *cache)
+{
+ cache->first_index = RADIX_TREE_MAP_MASK;
+ cache->tree_node = NULL;
+}
+
+/**
+ * radix_tree_cache_lookup - cached lookup page
+ * @root: radix tree root
+ * @cache: look-aside cache
+ * @index: index key
+ *
+ * Lookup the item at the position @index in the radix tree @root.
+ */
+static inline void *radix_tree_cache_lookup(struct radix_tree_root *root,
+ struct radix_tree_cache *cache,
+ unsigned long index)
+{
+ return radix_tree_cache_lookup_node(root, cache, index, 0);
+}
+
+static inline int radix_tree_cache_size(struct radix_tree_cache *cache)
+{
+ return RADIX_TREE_MAP_SIZE;
+}
+
+static inline int radix_tree_cache_full(struct radix_tree_cache *cache)
+{
+ return radix_tree_cache_count(cache) == radix_tree_cache_size(cache);
+}
+
+static inline int radix_tree_cache_first_index(struct radix_tree_cache *cache)
+{
+ return cache->first_index;
+}
+
#endif /* _LINUX_RADIX_TREE_H */
--- linux.orig/lib/radix-tree.c
+++ linux/lib/radix-tree.c
@@ -32,16 +32,7 @@
#include <linux/bitops.h>
-#ifdef __KERNEL__
-#define RADIX_TREE_MAP_SHIFT 6
-#else
-#define RADIX_TREE_MAP_SHIFT 3 /* For more stressful testing */
-#endif
#define RADIX_TREE_TAGS 2
-
-#define RADIX_TREE_MAP_SIZE (1UL << RADIX_TREE_MAP_SHIFT)
-#define RADIX_TREE_MAP_MASK (RADIX_TREE_MAP_SIZE-1)
-
#define RADIX_TREE_TAG_LONGS \
((RADIX_TREE_MAP_SIZE + BITS_PER_LONG - 1) / BITS_PER_LONG)
@@ -287,32 +278,86 @@ int radix_tree_insert(struct radix_tree_
}
EXPORT_SYMBOL(radix_tree_insert);
-static inline void **__lookup_slot(struct radix_tree_root *root,
- unsigned long index)
+/**
+ * radix_tree_lookup_node - low level lookup routine
+ * @root: radix tree root
+ * @index: index key
+ * @level: stop at that many levels from bottom
+ *
+ * Lookup the item at the position @index in the radix tree @root.
+ * The return value is:
+ * @level == 0: page at @index;
+ * @level == 1: the corresponding bottom level tree node;
+ * @level < height: (height - @level)th level tree node;
+ * @level >= height: root node.
+ */
+void *radix_tree_lookup_node(struct radix_tree_root *root,
+ unsigned long index, unsigned int level)
{
unsigned int height, shift;
- struct radix_tree_node **slot;
+ struct radix_tree_node *slot;
height = root->height;
if (index > radix_tree_maxindex(height))
return NULL;
shift = (height-1) * RADIX_TREE_MAP_SHIFT;
- slot = &root->rnode;
+ slot = root->rnode;
- while (height > 0) {
- if (*slot == NULL)
+ while (height > level) {
+ if (slot == NULL)
return NULL;
- slot = (struct radix_tree_node **)
- ((*slot)->slots +
- ((index >> shift) & RADIX_TREE_MAP_MASK));
+ slot = slot->slots[(index >> shift) & RADIX_TREE_MAP_MASK];
shift -= RADIX_TREE_MAP_SHIFT;
height--;
}
- return (void **)slot;
+ return slot;
}
+EXPORT_SYMBOL(radix_tree_lookup_node);
+
+/**
+ * radix_tree_cache_lookup_node - cached lookup node
+ * @root: radix tree root
+ * @cache: look-aside cache
+ * @index: index key
+ *
+ * Lookup the item at the position @index in the radix tree @root,
+ * and return the node @level levels from the bottom in the search path.
+ * @cache stores the last accessed upper level tree node by this
+ * function, and is always checked first before searching in the tree.
+ * It can improve speed for access patterns with strong locality.
+ * NOTE:
+ * - The cache becomes invalid on leaving the lock;
+ * - Do not intermix calls with different @level.
+ */
+void *radix_tree_cache_lookup_node(struct radix_tree_root *root,
+ struct radix_tree_cache *cache,
+ unsigned long index, unsigned int level)
+{
+ struct radix_tree_node *node;
+ unsigned long i;
+ unsigned long mask;
+
+ if (level >= root->height)
+ return root->rnode;
+
+ i = ((index >> (level * RADIX_TREE_MAP_SHIFT)) & RADIX_TREE_MAP_MASK);
+ mask = ~((RADIX_TREE_MAP_SIZE << (level * RADIX_TREE_MAP_SHIFT)) - 1);
+
+ if ((index & mask) == cache->first_index)
+ return cache->tree_node->slots[i];
+
+ node = radix_tree_lookup_node(root, index, level + 1);
+ if (!node)
+ return 0;
+
+ cache->tree_node = node;
+ cache->first_index = (index & mask);
+ return node->slots[i];
+}
+EXPORT_SYMBOL(radix_tree_cache_lookup_node);
/**
* radix_tree_lookup_slot - lookup a slot in a radix tree
@@ -324,25 +369,134 @@ static inline void **__lookup_slot(struc
*/
void **radix_tree_lookup_slot(struct radix_tree_root *root, unsigned long index)
{
- return __lookup_slot(root, index);
+ struct radix_tree_node *node;
+
+ node = radix_tree_lookup_node(root, index, 1);
+ return node->slots + (index & RADIX_TREE_MAP_MASK);
}
EXPORT_SYMBOL(radix_tree_lookup_slot);
/**
- * radix_tree_lookup - perform lookup operation on a radix tree
+ * radix_tree_cache_count - items in the cached node
+ * @cache: radix tree look-aside cache
+ *
+ * Query the number of items contained in the cached node.
+ */
+int radix_tree_cache_count(struct radix_tree_cache *cache)
+{
+ if (!(cache->first_index & RADIX_TREE_MAP_MASK))
+ return cache->tree_node->count;
+ else
+ return 0;
+}
+EXPORT_SYMBOL(radix_tree_cache_count);
+
+/**
+ * radix_tree_lookup_head - lookup the head index
* @root: radix tree root
* @index: index key
+ * @max_scan: max items to scan
*
- * Lookup the item at the position @index in the radix tree @root.
+ * Lookup head index of the segment which contains @index. A segment is
+ * a set of continuous pages in a file.
+ * CASE RETURN VALUE
+ * no page at @index (not head) = @index + 1
+ * found in the range @index - @max_scan < (head index) <= @index
+ * not found in range (unfinished head) <= @index - @max_scan
*/
-void *radix_tree_lookup(struct radix_tree_root *root, unsigned long index)
+unsigned long radix_tree_lookup_head(struct radix_tree_root *root,
+ unsigned long index, unsigned int max_scan)
{
- void **slot;
+ struct radix_tree_cache cache;
+ struct radix_tree_node *node;
+ int i;
+ unsigned long origin;
- slot = __lookup_slot(root, index);
- return slot != NULL ? *slot : NULL;
+ origin = index;
+ if (unlikely(max_scan > index))
+ max_scan = index;
+ radix_tree_cache_init(&cache);
+
+next_node:
+ if (origin - index > max_scan)
+ goto out;
+
+ node = radix_tree_cache_lookup_node(root, &cache, index, 1);
+ if (!node)
+ goto out;
+
+ if (node->count == RADIX_TREE_MAP_SIZE) {
+ if (index < RADIX_TREE_MAP_SIZE) {
+ index = -1;
+ goto out;
+ }
+ index = (index - RADIX_TREE_MAP_SIZE) | RADIX_TREE_MAP_MASK;
+ goto next_node;
+ }
+
+ for (i = index & RADIX_TREE_MAP_MASK; i >= 0; i--, index--) {
+ if (!node->slots[i])
+ goto out;
+ }
+
+ goto next_node;
+
+out:
+ return index + 1;
+}
+EXPORT_SYMBOL(radix_tree_lookup_head);
+
+/**
+ * radix_tree_lookup_tail - lookup the tail index
+ * @root: radix tree root
+ * @index: index key
+ * @max_scan: max items to scan
+ *
+ * Lookup tail(pass the end) index of the segment which contains @index.
+ * A segment is a set of continuous pages in a file.
+ * CASE RETURN VALUE
+ * found in the range @index <= (tail index) < @index + @max_scan
+ * not found in range @index + @max_scan <= (non tail)
+ */
+unsigned long radix_tree_lookup_tail(struct radix_tree_root *root,
+ unsigned long index, unsigned int max_scan)
+{
+ struct radix_tree_cache cache;
+ struct radix_tree_node *node;
+ int i;
+ unsigned long origin;
+
+ origin = index;
+ if (unlikely(index + max_scan < index))
+ max_scan = LONG_MAX - index;
+ radix_tree_cache_init(&cache);
+
+next_node:
+ if (index - origin >= max_scan)
+ goto out;
+
+ node = radix_tree_cache_lookup_node(root, &cache, index, 1);
+ if (!node)
+ goto out;
+
+ if (node->count == RADIX_TREE_MAP_SIZE) {
+ index = (index | RADIX_TREE_MAP_MASK) + 1;
+ if (unlikely(!index))
+ goto out;
+ goto next_node;
+ }
+
+ for (i = index & RADIX_TREE_MAP_MASK; i < RADIX_TREE_MAP_SIZE; i++, index++) {
+ if (!node->slots[i])
+ goto out;
+ }
+
+ goto next_node;
+
+out:
+ return index;
}
-EXPORT_SYMBOL(radix_tree_lookup);
+EXPORT_SYMBOL(radix_tree_lookup_tail);
/**
* radix_tree_tag_set - set a tag on a radix tree node
--
^ permalink raw reply [flat|nested] 15+ messages in thread
* [PATCH 02/12] readahead: some preparation
2005-12-16 13:07 [PATCH 00/12] Adaptive read-ahead V10 Wu Fengguang
2005-12-16 13:07 ` [PATCH 01/12] radixtree: look-aside cache Wu Fengguang
@ 2005-12-16 13:07 ` Wu Fengguang
2005-12-16 13:07 ` [PATCH 03/12] readahead: call scheme Wu Fengguang
` (9 subsequent siblings)
11 siblings, 0 replies; 15+ messages in thread
From: Wu Fengguang @ 2005-12-16 13:07 UTC (permalink / raw)
To: linux-kernel; +Cc: Andrew Morton, Wu Fengguang
[-- Attachment #1: readahead-prepare.patch --]
[-- Type: text/plain, Size: 9327 bytes --]
Some random changes that do not fit in elsewhere.
Signed-off-by: Wu Fengguang <wfg@mail.ustc.edu.cn>
---
include/linux/mm.h | 7 +
mm/filemap.c | 4 +
mm/readahead.c | 197 ++++++++++++++++++++++++++++++++++++++++++++++++++---
3 files changed, 199 insertions(+), 9 deletions(-)
--- linux.orig/include/linux/mm.h
+++ linux/include/linux/mm.h
@@ -1008,6 +1008,13 @@ void handle_ra_miss(struct address_space
struct file_ra_state *ra, pgoff_t offset);
unsigned long max_sane_readahead(unsigned long nr);
+#ifdef CONFIG_DEBUG_FS
+extern u32 readahead_debug_level;
+#define READAHEAD_DEBUG_LEVEL(n) (readahead_debug_level >= n)
+#else
+#define READAHEAD_DEBUG_LEVEL(n) (0)
+#endif
+
/* Do stack extension */
extern int expand_stack(struct vm_area_struct *vma, unsigned long address);
#ifdef CONFIG_IA64
--- linux.orig/mm/readahead.c
+++ linux/mm/readahead.c
@@ -15,13 +15,63 @@
#include <linux/backing-dev.h>
#include <linux/pagevec.h>
+/* The default max/min read-ahead pages. */
+#define KB(size) (((size)*1024 + PAGE_CACHE_SIZE-1) / PAGE_CACHE_SIZE)
+#define MAX_RA_PAGES KB(VM_MAX_READAHEAD)
+#define MIN_RA_PAGES KB(VM_MIN_READAHEAD)
+
+#define next_page(pg) (list_entry((pg)->lru.prev, struct page, lru))
+#define prev_page(pg) (list_entry((pg)->lru.next, struct page, lru))
+
+/*
+ * Debug facilities.
+ */
+#ifdef CONFIG_DEBUG_FS
+#define DEBUG_READAHEAD
+#endif
+
+#ifdef DEBUG_READAHEAD
+#define dprintk(args...) \
+ do { if (READAHEAD_DEBUG_LEVEL(1)) printk(KERN_DEBUG args); } while(0)
+#define ddprintk(args...) \
+ do { if (READAHEAD_DEBUG_LEVEL(2)) printk(KERN_DEBUG args); } while(0)
+#else
+#define dprintk(args...) do { } while(0)
+#define ddprintk(args...) do { } while(0)
+#endif
+
+#ifdef DEBUG_READAHEAD
+#include <linux/jiffies.h>
+#include <linux/debugfs.h>
+#include <linux/seq_file.h>
+#include <linux/init.h>
+
+u32 readahead_debug_level = 0;
+
+static int __init readahead_init(void)
+{
+ struct dentry *root;
+
+ root = debugfs_create_dir("readahead", NULL);
+
+ debugfs_create_u32("debug_level", 0644, root, &readahead_debug_level);
+
+ return 0;
+}
+
+module_init(readahead_init)
+#else /* !DEBUG_READAHEAD */
+
+#endif /* DEBUG_READAHEAD */
+
+
void default_unplug_io_fn(struct backing_dev_info *bdi, struct page *page)
{
}
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,
.state = 0,
.capabilities = BDI_CAP_MAP_COPY,
.unplug_io_fn = default_unplug_io_fn,
@@ -50,7 +100,7 @@ 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 ra_off(struct file_ra_state *ra)
@@ -258,10 +308,11 @@ 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;
+ struct page *page = NULL;
unsigned long end_index; /* The last page we want to read */
LIST_HEAD(page_pool);
int page_idx;
@@ -271,7 +322,7 @@ __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.
@@ -284,8 +335,14 @@ __do_page_cache_readahead(struct address
break;
page = radix_tree_lookup(&mapping->page_tree, page_offset);
- if (page)
+ if (page) {
+#ifdef READAHEAD_NONBLOCK
+ if (prefer_adaptive_readahead() &&
+ page_idx == nr_to_read - lookahead_size)
+ SetPageReadahead(page);
+#endif
continue;
+ }
read_unlock_irq(&mapping->tree_lock);
page = page_cache_alloc_cold(mapping);
@@ -294,6 +351,9 @@ __do_page_cache_readahead(struct address
break;
page->index = page_offset;
list_add(&page->lru, &page_pool);
+ if (prefer_adaptive_readahead() &&
+ page_idx == nr_to_read - lookahead_size)
+ SetPageReadahead(page);
ret++;
}
read_unlock_irq(&mapping->tree_lock);
@@ -330,7 +390,7 @@ 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;
@@ -377,7 +437,7 @@ int do_page_cache_readahead(struct addre
if (bdi_read_congested(mapping->backing_dev_info))
return -1;
- return __do_page_cache_readahead(mapping, filp, offset, nr_to_read);
+ return __do_page_cache_readahead(mapping, filp, offset, nr_to_read, 0);
}
/*
@@ -397,7 +457,10 @@ 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);
+
+ 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);
}
@@ -575,3 +638,119 @@ 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 pressures.
+ *
+ * It employs two methods to estimate the max thrashing safe read-ahead size:
+ * 1. state based - the default one
+ * 2. context based - the fail safe 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.
+ *
+ *
+ * Here are some variable names used frequently:
+ *
+ * |<------- la_size ------>|
+ * +-----------------------------------------+
+ * | # |
+ * +-----------------------------------------+
+ * ra_index -->|<---------------- ra_size -------------->|
+ *
+ */
+
+/*
+ * The nature of read-ahead allows most tests to fail or even be wrong.
+ * Here we just do not bother to call get_page(), it's meaningless anyway.
+ */
+static inline struct page *__find_page(struct address_space *mapping,
+ pgoff_t offset)
+{
+ return radix_tree_lookup(&mapping->page_tree, offset);
+}
+
+static inline struct page *find_page(struct address_space *mapping,
+ pgoff_t offset)
+{
+ struct page *page;
+
+ read_lock_irq(&mapping->tree_lock);
+ page = __find_page(mapping, offset);
+ read_unlock_irq(&mapping->tree_lock);
+#ifdef DEBUG_READAHEAD_RADIXTREE
+ if (page)
+ BUG_ON(page->index != offset);
+#endif
+ return page;
+}
+
+/*
+ * Move pages in danger (of thrashing) to the head of inactive_list.
+ * Not expected to happen frequently.
+ */
+static int rescue_pages(struct page *page, pgoff_t nr_pages)
+{
+ unsigned long pgrescue;
+ pgoff_t index;
+ struct address_space *mapping;
+ struct zone *zone;
+
+ BUG_ON(!nr_pages || !page);
+ pgrescue = 0;
+ index = page_index(page);
+ mapping = page_mapping(page);
+
+ 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 = next_page(page);
+ 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);
+
+ page = find_page(mapping, index);
+ if (!page)
+ goto out;
+ }
+out_unlock:
+ spin_unlock_irq(&zone->lru_lock);
+out:
+ ra_account(NULL, RA_EVENT_READAHEAD_RESCUE, pgrescue);
+
+ return nr_pages ? index : 0;
+}
--- linux.orig/mm/filemap.c
+++ linux/mm/filemap.c
@@ -780,6 +780,10 @@ void do_generic_mapping_read(struct addr
if (!isize)
goto out;
+ if (READAHEAD_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;
--
^ permalink raw reply [flat|nested] 15+ messages in thread
* [PATCH 03/12] readahead: call scheme
2005-12-16 13:07 [PATCH 00/12] Adaptive read-ahead V10 Wu Fengguang
2005-12-16 13:07 ` [PATCH 01/12] radixtree: look-aside cache Wu Fengguang
2005-12-16 13:07 ` [PATCH 02/12] readahead: some preparation Wu Fengguang
@ 2005-12-16 13:07 ` Wu Fengguang
2005-12-16 13:07 ` [PATCH 04/12] readahead: parameters Wu Fengguang
` (8 subsequent siblings)
11 siblings, 0 replies; 15+ messages in thread
From: Wu Fengguang @ 2005-12-16 13:07 UTC (permalink / raw)
To: linux-kernel; +Cc: Andrew Morton, Wu Fengguang
[-- Attachment #1: readahead-call-scheme.patch --]
[-- Type: text/plain, Size: 13708 bytes --]
An new page flag PG_readahead is introduced as a look-ahead mark.
The look-ahead mark corresponds to `ahead_start' of the current logic.
The read-ahead logic is called when
- read reaches a look-ahead mark;
- read on a non-present page.
And ra_access() is called on every page reference to maintain the cache_hit
counter.
This scheme has the following benefits:
- makes all stateful/stateless methods happy;
- eliminates the cache hit problem naturally;
- lives in harmony with application managed read-aheads via
fadvise/madvise.
Signed-off-by: Wu Fengguang <wfg@mail.ustc.edu.cn>
---
include/linux/mm.h | 13 +++
include/linux/page-flags.h | 5 +
mm/filemap.c | 74 ++++++++++++++++---
mm/page_alloc.c | 2
mm/readahead.c | 174 +++++++++++++++++++++++++++++++++++++++++++++
5 files changed, 257 insertions(+), 11 deletions(-)
--- linux.orig/include/linux/page-flags.h
+++ linux/include/linux/page-flags.h
@@ -76,6 +76,7 @@
#define PG_reclaim 17 /* To be reclaimed asap */
#define PG_nosave_free 18 /* Free, should not be written */
#define PG_uncached 19 /* Page has been mapped as uncached */
+#define PG_readahead 20 /* check readahead when reading this page */
/*
* Global page accounting. One instance per CPU. Only unsigned longs are
@@ -314,6 +315,10 @@ extern void __mod_page_state(unsigned lo
#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.orig/include/linux/mm.h
+++ linux/include/linux/mm.h
@@ -1007,6 +1007,13 @@ 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);
+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 fastcall ra_access(struct file_ra_state *ra, struct page *page);
#ifdef CONFIG_DEBUG_FS
extern u32 readahead_debug_level;
@@ -1015,6 +1022,12 @@ extern u32 readahead_debug_level;
#define READAHEAD_DEBUG_LEVEL(n) (0)
#endif
+extern int readahead_ratio;
+static inline int prefer_adaptive_readahead(void)
+{
+ return readahead_ratio > 9;
+}
+
/* Do stack extension */
extern int expand_stack(struct vm_area_struct *vma, unsigned long address);
#ifdef CONFIG_IA64
--- linux.orig/mm/page_alloc.c
+++ linux/mm/page_alloc.c
@@ -539,7 +539,7 @@ 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);
--- linux.orig/mm/filemap.c
+++ linux/mm/filemap.c
@@ -766,10 +766,12 @@ 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;
@@ -802,16 +804,42 @@ 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)) {
+ 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)) {
+ 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;
+
+ ra_access(&ra, page);
+ if (READAHEAD_DEBUG_LEVEL(7))
+ printk(KERN_DEBUG "read-file(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:
@@ -846,7 +874,6 @@ page_ok:
index += offset >> PAGE_CACHE_SHIFT;
offset &= ~PAGE_CACHE_MASK;
- page_cache_release(page);
if (ret == nr && desc->count)
continue;
goto out;
@@ -858,7 +885,6 @@ 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;
}
@@ -888,7 +914,6 @@ readpage:
* invalidate_inode_pages got it
*/
unlock_page(page);
- page_cache_release(page);
goto find_page;
}
unlock_page(page);
@@ -909,7 +934,6 @@ 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;
}
@@ -918,7 +942,6 @@ readpage:
if (index == end_index) {
nr = ((isize - 1) & ~PAGE_CACHE_MASK) + 1;
if (nr <= offset) {
- page_cache_release(page);
goto out;
}
}
@@ -928,7 +951,6 @@ readpage:
readpage_error:
/* UHHUH! A synchronous read error occurred. Report it */
desc->error = error;
- page_cache_release(page);
goto out;
no_cached_page:
@@ -953,15 +975,22 @@ 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);
}
@@ -1240,6 +1269,7 @@ 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:
@@ -1257,19 +1287,33 @@ 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);
+
/*
* Do we have something in the page cache already?
*/
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++;
@@ -1306,6 +1350,14 @@ retry_find:
if (!did_readaround)
ra->mmap_hit++;
+ ra_access(ra, page);
+ if (READAHEAD_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.
@@ -1320,6 +1372,8 @@ success:
mark_page_accessed(page);
if (type)
*type = majmin;
+ if (prefer_adaptive_readahead())
+ ra->prev_page = page->index;
return page;
outside_data_content:
--- linux.orig/mm/readahead.c
+++ linux/mm/readahead.c
@@ -20,6 +20,44 @@
#define MAX_RA_PAGES KB(VM_MAX_READAHEAD)
#define MIN_RA_PAGES KB(VM_MIN_READAHEAD)
+/* 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_NEWFILE,
+ RA_CLASS_STATE,
+ RA_CLASS_CONTEXT,
+ RA_CLASS_CONTEXT_ACCELERATED,
+ RA_CLASS_BACKWARD,
+ RA_CLASS_RANDOM_THRASHING,
+ RA_CLASS_RANDOM_SEEK,
+ RA_CLASS_END,
+};
+
+/* Read-ahead events to be accounted. */
+enum ra_event {
+ RA_EVENT_CACHE_MISS, /* read cache misses */
+ RA_EVENT_READRANDOM, /* random reads */
+ RA_EVENT_IO_CONGESTION, /* io congestion */
+ RA_EVENT_IO_CACHE_HIT, /* canceled io due to cache hit */
+ RA_EVENT_IO_BLOCK, /* read on locked page */
+
+ 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 memory mapped file */
+ RA_EVENT_READAHEAD_EOF, /* read-ahead reaches EOF */
+ RA_EVENT_READAHEAD_SHRINK, /* ra_size under previous la_size */
+ RA_EVENT_READAHEAD_THRASHING, /* read-ahead thrashing happened */
+ RA_EVENT_READAHEAD_MUTILATE, /* read-ahead request mutilated */
+ RA_EVENT_READAHEAD_RESCUE, /* read-ahead rescued */
+
+ RA_EVENT_END
+};
+
#define next_page(pg) (list_entry((pg)->lru.prev, struct page, lru))
#define prev_page(pg) (list_entry((pg)->lru.next, struct page, lru))
@@ -754,3 +792,139 @@ out:
return nr_pages ? index : 0;
}
+
+/*
+ * This is the entry point of the adaptive read-ahead logic.
+ *
+ * It is only called on two conditions:
+ * 1. page == NULL
+ * A cache miss happened, it can be either a random read or a sequential one.
+ * 2. page != NULL
+ * There is a look-ahead mark(PG_readahead) from a previous sequential read.
+ * It's time to do some checking and submit the next read-ahead IO.
+ *
+ * That has the merits of:
+ * - makes all stateful/stateless methods happy;
+ * - eliminates the cache hit problem naturally;
+ * - lives in harmony with application managed read-aheads via fadvise/madvise.
+ */
+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;
+
+ if (page) {
+ if(!TestClearPageReadahead(page))
+ return 0;
+ if (bdi_read_congested(mapping->backing_dev_info))
+ 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 newfile_readahead(mapping, filp, ra, end_index, ra_min);
+
+ /*
+ * State based sequential read-ahead.
+ */
+ if (!disable_stateful_method() &&
+ ((page && ra_has_index(ra, index)) ||
+ index == ra->readahead_index)) {
+ ra->lookahead_index = index;
+ if (ra_cache_hit_ok(ra) || size >= ra_max)
+ return state_based_readahead(mapping, filp, ra, page,
+ index, size, ra_max);
+ }
+
+ /*
+ * Backward read-ahead.
+ */
+ if (try_read_backward(ra, begin_index, end_index, size, ra_min, ra_max))
+ return ra_dispatch(ra, mapping, filp);
+
+ /*
+ * Context based sequential read-ahead.
+ */
+ ret = try_context_based_readahead(mapping, ra, prev_page, page,
+ index, size, 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_random_readahead(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_READRANDOM, size);
+ dprintk("readrandom(ino=%lu, pages=%lu, index=%lu-%lu-%lu) = %lu\n",
+ mapping->host->i_ino, mapping->nrpages,
+ begin_index, index, end_index, size);
+
+ return size;
+}
+
+/*
+ * Call me!
+ */
+void fastcall ra_access(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->cache_hit++;
+
+ if (page->index >= ra->ra_index)
+ ra_account(ra, RA_EVENT_READAHEAD_HIT, 1);
+ else
+ ra_account(ra, RA_EVENT_READAHEAD_HIT, -1);
+}
+
--
^ permalink raw reply [flat|nested] 15+ messages in thread
* [PATCH 04/12] readahead: parameters
2005-12-16 13:07 [PATCH 00/12] Adaptive read-ahead V10 Wu Fengguang
` (2 preceding siblings ...)
2005-12-16 13:07 ` [PATCH 03/12] readahead: call scheme Wu Fengguang
@ 2005-12-16 13:07 ` Wu Fengguang
2005-12-16 13:07 ` [PATCH 05/12] readahead: state based method Wu Fengguang
` (7 subsequent siblings)
11 siblings, 0 replies; 15+ messages in thread
From: Wu Fengguang @ 2005-12-16 13:07 UTC (permalink / raw)
To: linux-kernel; +Cc: Andrew Morton, Wu Fengguang
[-- Attachment #1: readahead-parameters.patch --]
[-- Type: text/plain, Size: 5866 bytes --]
- new sysctl entries in /proc/sys/vm:
- readahead_ratio = 1
- readahead_hit_rate = 2
- dynamic minimal/initial read-ahead size.
For now, different ranges of readahead_ratio select different read-ahead
code path:
condition action
===========================================================
readahead_ratio == 0 disable read-ahead
readahead_ratio < 9 select old read-ahead logic
readahead_ratio >= 9 select new read-ahead logic
Signed-off-by: Wu Fengguang <wfg@mail.ustc.edu.cn>
---
Documentation/sysctl/vm.txt | 38 ++++++++++++++++++++++++++++++++++++++
include/linux/sysctl.h | 2 ++
kernel/sysctl.c | 23 +++++++++++++++++++++++
mm/readahead.c | 35 +++++++++++++++++++++++++++++++++++
4 files changed, 98 insertions(+)
--- linux.orig/Documentation/sysctl/vm.txt
+++ linux/Documentation/sysctl/vm.txt
@@ -28,6 +28,8 @@ Currently, these files are in /proc/sys/
- block_dump
- drop-caches
- swap_prefetch
+- readahead_ratio
+- readahead_hit_rate
==============================================================
@@ -132,3 +134,39 @@ laptop_mode is enabled and then it is te
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.
+
+Set it to a low value if you have not enough memory to counteract
+the I/O load fluctuations. But if there's plenty of memory, set it
+to a larger value might help speedup reads.
+
+readahead_ratio also selects the read-ahead logic:
+0: disable read-ahead totally
+1-9: select the well tested old read-ahead logic
+10-inf: select the new adaptive read-ahead logic
+
+The default value is 1.
+For the new adaptive read-ahead, reasonable values would be 50-100.
+
+==============================================================
+
+readahead_hit_rate
+
+This is the max allowed value of (read-ahead-pages : accessed-pages).
+Useful only when (readahead_ratio >= 10). If the previous read-ahead
+request has bad hit rate, kernel will be very conservative to issue
+the next read-ahead.
+
+A large value helps speedup some sparse access patterns, at the cost
+of more memory consumption. It is recommended to keep the value below
+(max-readahead-pages / 8).
+
+The default value is 2.
--- linux.orig/include/linux/sysctl.h
+++ linux/include/linux/sysctl.h
@@ -184,6 +184,8 @@ enum
VM_DROP_PAGECACHE=29, /* int: nuke lots of pagecache */
VM_PERCPU_PAGELIST_FRACTION=30,/* int: fraction of pages in each percpu_pagelist */
VM_SWAP_PREFETCH=31, /* int: amount to swap prefetch */
+ VM_READAHEAD_RATIO=32, /* percent of read-ahead size to thrashing-threshold */
+ VM_READAHEAD_HIT_RATE=33, /* one accessed page legitimizes so many read-ahead pages */
};
/* CTL_NET names: */
--- linux.orig/kernel/sysctl.c
+++ linux/kernel/sysctl.c
@@ -70,6 +70,8 @@ extern int printk_ratelimit_burst;
extern int pid_max_min, pid_max_max;
extern int sysctl_drop_caches;
extern int percpu_pagelist_fraction;
+extern int readahead_ratio;
+extern int readahead_hit_rate;
#if defined(CONFIG_X86_LOCAL_APIC) && defined(CONFIG_X86)
int unknown_nmi_panic;
@@ -671,6 +673,7 @@ static ctl_table kern_table[] = {
/* Constants for minimum and maximum testing in vm_table.
We use these as one-element integer vectors. */
static int zero;
+static int one = 1;
static int one_hundred = 100;
@@ -889,6 +892,26 @@ 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 = 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,
+ },
{ .ctl_name = 0 }
};
--- linux.orig/mm/readahead.c
+++ linux/mm/readahead.c
@@ -20,6 +20,20 @@
#define MAX_RA_PAGES KB(VM_MAX_READAHEAD)
#define MIN_RA_PAGES KB(VM_MIN_READAHEAD)
+/* 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 = 1;
+EXPORT_SYMBOL(readahead_ratio);
+
+/* Readahead as long as cache hit ratio keeps above 1/##. */
+int readahead_hit_rate = 2;
+EXPORT_SYMBOL(readahead_hit_rate);
+
/* Detailed classification of read-ahead behaviors. */
#define RA_CLASS_SHIFT 4
#define RA_CLASS_MASK ((1 << RA_CLASS_SHIFT) - 1)
@@ -794,6 +808,27 @@ out:
}
/*
+ * ra_size is mainly determined by:
+ * 1. sequential-start: min(MIN_RA_PAGES + (pages>>14), KB(128))
+ * 2. sequential-max: min(ra->ra_pages, 0xFFFF)
+ * 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
+ */
+static inline void get_readahead_bounds(struct file_ra_state *ra,
+ unsigned long *ra_min,
+ unsigned long *ra_max)
+{
+ unsigned long pages;
+
+ pages = node_free_and_cold_pages();
+ *ra_max = min(min(pages/2, 0xFFFFUL), ra->ra_pages);
+ *ra_min = min(min(MIN_RA_PAGES + (pages>>14), KB(128)), *ra_max/2);
+}
+
+/*
* This is the entry point of the adaptive read-ahead logic.
*
* It is only called on two conditions:
--
^ permalink raw reply [flat|nested] 15+ messages in thread
* [PATCH 05/12] readahead: state based method
2005-12-16 13:07 [PATCH 00/12] Adaptive read-ahead V10 Wu Fengguang
` (3 preceding siblings ...)
2005-12-16 13:07 ` [PATCH 04/12] readahead: parameters Wu Fengguang
@ 2005-12-16 13:07 ` Wu Fengguang
2005-12-16 13:07 ` [PATCH 06/12] readahead: context " Wu Fengguang
` (6 subsequent siblings)
11 siblings, 0 replies; 15+ messages in thread
From: Wu Fengguang @ 2005-12-16 13:07 UTC (permalink / raw)
To: linux-kernel; +Cc: Andrew Morton, Wu Fengguang
[-- Attachment #1: readahead-method-stateful.patch --]
[-- Type: text/plain, Size: 16116 bytes --]
This is the fast code path.
Major steps:
- estimate a thrashing safe ra_size;
- assemble the next read-ahead request in file_ra_state;
- submit it.
Signed-off-by: Wu Fengguang <wfg@mail.ustc.edu.cn>
---
include/linux/fs.h | 37 +++--
include/linux/mm.h | 6
mm/memory.c | 1
mm/readahead.c | 368 ++++++++++++++++++++++++++++++++++++++++++++++++++++-
mm/swap.c | 2
mm/vmscan.c | 3
6 files changed, 403 insertions(+), 14 deletions(-)
--- linux.orig/include/linux/fs.h
+++ linux/include/linux/fs.h
@@ -601,19 +601,36 @@ struct fown_struct {
* Track a single file's readahead state
*/
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 */
- unsigned long mmap_hit; /* Cache hit stat for mmap accesses */
- unsigned long mmap_miss; /* Cache miss stat for mmap accesses */
+ union {
+ struct { /* conventional read-ahead */
+ unsigned long start; /* Current window */
+ unsigned long size;
+ unsigned long ahead_start; /* Ahead window */
+ unsigned long ahead_size;
+ };
+
+ struct { /* adaptive read-ahead */
+ pgoff_t la_index;
+ pgoff_t ra_index;
+ pgoff_t lookahead_index;
+ pgoff_t readahead_index;
+ unsigned long age;
+ };
+ };
+
+ /* mmap read-around */
+ unsigned long mmap_hit; /* Cache hit stat for mmap accesses */
+ unsigned long mmap_miss; /* Cache miss stat for mmap accesses */
+
+ /* common ones */
+ uint64_t cache_hit; /* cache hit count*/
+ unsigned long flags; /* ra flags RA_FLAG_xxx*/
+ 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_MMAP (1UL<<31) /* mmaped page access */
struct file {
/*
--- linux.orig/include/linux/mm.h
+++ linux/include/linux/mm.h
@@ -1028,6 +1028,12 @@ static inline int prefer_adaptive_readah
return readahead_ratio > 9;
}
+DECLARE_PER_CPU(unsigned long, readahead_aging);
+static inline void inc_readahead_aging(void)
+{
+ __get_cpu_var(readahead_aging)++;
+}
+
/* Do stack extension */
extern int expand_stack(struct vm_area_struct *vma, unsigned long address);
#ifdef CONFIG_IA64
--- linux.orig/mm/memory.c
+++ linux/mm/memory.c
@@ -1966,6 +1966,7 @@ static int do_anonymous_page(struct mm_s
page_table = pte_offset_map_lock(mm, pmd, address, &ptl);
if (!pte_none(*page_table))
goto release;
+ inc_readahead_aging();
inc_mm_counter(mm, anon_rss);
lru_cache_add_active(page);
page_add_new_anon_rmap(page, vma, address);
--- linux.orig/mm/vmscan.c
+++ linux/mm/vmscan.c
@@ -447,6 +447,9 @@ static int shrink_list(struct list_head
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))
--- linux.orig/mm/swap.c
+++ linux/mm/swap.c
@@ -124,6 +124,8 @@ void fastcall mark_page_accessed(struct
ClearPageReferenced(page);
} else if (!PageReferenced(page)) {
SetPageReferenced(page);
+ if (PageLRU(page))
+ inc_readahead_aging();
}
}
--- linux.orig/mm/readahead.c
+++ linux/mm/readahead.c
@@ -34,6 +34,13 @@ EXPORT_SYMBOL(readahead_ratio);
int readahead_hit_rate = 2;
EXPORT_SYMBOL(readahead_hit_rate);
+/*
+ * Measures the aging process of cold pages.
+ * Mainly increased on fresh page references to make it smooth.
+ */
+DEFINE_PER_CPU(unsigned long, readahead_aging);
+EXPORT_PER_CPU_SYMBOL(readahead_aging);
+
/* Detailed classification of read-ahead behaviors. */
#define RA_CLASS_SHIFT 4
#define RA_CLASS_MASK ((1 << RA_CLASS_SHIFT) - 1)
@@ -99,6 +106,7 @@ enum ra_event {
#include <linux/init.h>
u32 readahead_debug_level = 0;
+u32 debug_disable_stateful_method = 0;
static int __init readahead_init(void)
{
@@ -107,13 +115,26 @@ static int __init readahead_init(void)
root = debugfs_create_dir("readahead", NULL);
debugfs_create_u32("debug_level", 0644, root, &readahead_debug_level);
+ debugfs_create_bool("disable_stateful_method", 0644, root,
+ &debug_disable_stateful_method);
return 0;
}
module_init(readahead_init)
+
+static inline int disable_stateful_method(void)
+{
+ return debug_disable_stateful_method;
+}
+
#else /* !DEBUG_READAHEAD */
+static inline int disable_stateful_method(void)
+{
+ return 0;
+}
+
#endif /* DEBUG_READAHEAD */
@@ -558,7 +579,7 @@ 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]()
@@ -808,6 +829,345 @@ out:
}
/*
+ * State based calculation of read-ahead request.
+ *
+ * This figure shows the meaning of file_ra_state members:
+ *
+ * chunk A chunk B
+ * +---------------------------+-------------------------------------------+
+ * | # | # |
+ * +---------------------------+-------------------------------------------+
+ * ^ ^ ^ ^
+ * la_index ra_index lookahead_index readahead_index
+ */
+
+/*
+ * The node's effective length of inactive_list(s).
+ */
+static unsigned long node_free_and_cold_pages(void)
+{
+ unsigned int i;
+ unsigned long sum = 0;
+ struct zone *zones = NODE_DATA(numa_node_id())->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;
+}
+
+/*
+ * The node's accumulated aging activities.
+ */
+static unsigned long node_readahead_aging(void)
+{
+ unsigned long cpu;
+ unsigned long sum = 0;
+ cpumask_t mask = node_to_cpumask(numa_node_id());
+
+ for_each_cpu_mask(cpu, mask)
+ sum += per_cpu(readahead_aging, cpu);
+
+ return sum;
+}
+
+/*
+ * The 64bit cache_hit stores three accumulated values and one counter value.
+ * MSB LSB
+ * 3333333333333333 : 2222222222222222 : 1111111111111111 : 0000000000000000
+ */
+static inline int ra_cache_hit(struct file_ra_state *ra, int nr)
+{
+ return (ra->cache_hit >> (nr * 16)) & 0xFFFF;
+}
+
+/*
+ * Conceptual code:
+ * ra_cache_hit(ra, 1) += ra_cache_hit(ra, 0);
+ * ra_cache_hit(ra, 0) = 0;
+ */
+static inline void ra_addup_cache_hit(struct file_ra_state *ra)
+{
+ int n;
+
+ n = ra_cache_hit(ra, 0);
+ ra->cache_hit -= n;
+ n <<= 16;
+ ra->cache_hit += n;
+}
+
+/*
+ * The read-ahead is deemed success if cache-hit-rate >= 1/readahead_hit_rate.
+ */
+static inline int ra_cache_hit_ok(struct file_ra_state *ra)
+{
+ return ra_cache_hit(ra, 0) * readahead_hit_rate >=
+ (ra->lookahead_index - ra->la_index);
+}
+
+/*
+ * Check if @index falls in the @ra request.
+ */
+static inline 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 inline 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->flags & RA_CLASS_MASK) << RA_CLASS_SHIFT;
+
+ ra->flags = flags | old_ra_class | ra_class;
+
+ ra_addup_cache_hit(ra);
+ if (ra_class != RA_CLASS_STATE)
+ ra->cache_hit <<= 16;
+
+ ra->age = node_readahead_aging();
+}
+
+/*
+ * Where is the old read-ahead and look-ahead?
+ */
+static inline 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 inline 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)
+{
+ pgoff_t eof_index;
+ unsigned long ra_size;
+ unsigned long la_size;
+ int actual;
+ enum ra_class ra_class;
+
+ ra_class = (ra->flags & RA_CLASS_MASK);
+ BUG_ON(ra_class == 0 || ra_class > RA_CLASS_END);
+
+ eof_index = ((i_size_read(mapping->host) - 1) >> PAGE_CACHE_SHIFT) + 1;
+ ra_size = ra->readahead_index - ra->ra_index;
+ la_size = ra->readahead_index - ra->lookahead_index;
+
+ /* Snap to EOF. */
+ if (unlikely(ra->ra_index >= eof_index))
+ return 0;
+ if (ra->readahead_index + ra_size / 2 > eof_index) {
+ if (ra_class == RA_CLASS_CONTEXT_ACCELERATED &&
+ eof_index > ra->lookahead_index + 1)
+ la_size = eof_index - ra->lookahead_index;
+ else
+ la_size = 0;
+ ra_size = eof_index - ra->ra_index;
+ ra_set_size(ra, ra_size, la_size);
+ }
+
+ actual = __do_page_cache_readahead(mapping, filp,
+ ra->ra_index, ra_size, la_size);
+
+#ifdef READAHEAD_NONBLOCK
+ if (actual < ra_size) {
+ struct page *page = find_page(mapping, ra->ra_index + actual);
+ if (page)
+ rescue_pages(page, ra_size);
+ }
+#endif
+
+ 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);
+ 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],
+ mapping->host->i_ino, ra->la_index,
+ ra->ra_index, ra_size, la_size, actual);
+
+ return actual;
+}
+
+/*
+ * Determine the request parameters from primitive values.
+ *
+ * It applies the following rules:
+ * - Substract ra_size by the old look-ahead to get real safe read-ahead;
+ * - Set new la_size according to the (still large) ra_size;
+ * - Apply upper limits;
+ * - Make sure stream_shift is not too small.
+ * (So that the next global_shift will not be too small.)
+ *
+ * Input:
+ * ra_size stores the estimated thrashing-threshold.
+ * la_size stores the look-ahead size of previous request.
+ */
+static inline int adjust_rala(unsigned long ra_max,
+ unsigned long *ra_size, unsigned long *la_size)
+{
+ unsigned long stream_shift = *la_size;
+
+ if (*ra_size > *la_size)
+ *ra_size -= *la_size;
+ else {
+ ra_account(NULL, RA_EVENT_READAHEAD_SHRINK, *ra_size);
+ return 0;
+ }
+
+ *la_size = *ra_size / LOOKAHEAD_RATIO;
+
+ if (*ra_size > ra_max)
+ *ra_size = ra_max;
+ if (*la_size > *ra_size)
+ *la_size = *ra_size;
+
+ stream_shift += (*ra_size - *la_size);
+ if (stream_shift < *ra_size / 4)
+ *la_size -= (*ra_size / 4 - stream_shift);
+
+ return 1;
+}
+
+/*
+ * 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 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 with light load(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 inline 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;
+
+ global_size = node_free_and_cold_pages();
+ global_shift = node_readahead_aging() - ra->age;
+ global_shift |= 1UL;
+ stream_shift = ra_cache_hit(ra, 0);
+
+ ra_size = stream_shift *
+ global_size * readahead_ratio / (100 * global_shift);
+
+ if (global_size > global_shift)
+ *remain = stream_shift *
+ (global_size - global_shift) / global_shift;
+ else
+ *remain = 0;
+
+ ddprintk("compute_thrashing_threshold: "
+ "ra=%lu=%lu*%lu/%lu, remain %lu for %lu\n",
+ ra_size, stream_shift, global_size, global_shift,
+ *remain, ra->readahead_index - ra->lookahead_index);
+
+ return ra_size;
+}
+
+/*
+ * Main function for file_ra_state based read-ahead.
+ */
+static inline 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 ra_size, unsigned long ra_max)
+{
+ unsigned long ra_old;
+ unsigned long la_size;
+ unsigned long remain_space;
+ unsigned long growth_limit;
+
+ la_size = ra->readahead_index - index;
+ ra_old = ra->readahead_index - ra->ra_index;
+ growth_limit = ra_size + (2 + readahead_ratio / 64) * ra_old +
+ (ra_max - ra_old) / 16;
+ ra_size = compute_thrashing_threshold(ra, &remain_space);
+
+ if (remain_space <= la_size && la_size > 1) {
+ rescue_pages(page, la_size);
+ return 0;
+ }
+
+ if (!adjust_rala(min(ra_max, growth_limit), &ra_size, &la_size))
+ return 0;
+
+ 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);
+}
+
+
+/*
* ra_size is mainly determined by:
* 1. sequential-start: min(MIN_RA_PAGES + (pages>>14), KB(128))
* 2. sequential-max: min(ra->ra_pages, 0xFFFF)
@@ -835,13 +1195,13 @@ static inline void get_readahead_bounds(
* 1. page == NULL
* A cache miss happened, it can be either a random read or a sequential one.
* 2. page != NULL
- * There is a look-ahead mark(PG_readahead) from a previous sequential read.
+ * There is a look-ahead mark (PG_readahead) from a previous sequential read.
* It's time to do some checking and submit the next read-ahead IO.
*
- * That has the merits of:
+ * That has the following merits:
* - makes all stateful/stateless methods happy;
* - eliminates the cache hit problem naturally;
- * - lives in harmony with application managed read-aheads via fadvise/madvise.
+ * - lives in harmony with application-managed read-aheads via fadvise/madvise.
*/
unsigned long
page_cache_readahead_adaptive(struct address_space *mapping,
--
^ permalink raw reply [flat|nested] 15+ messages in thread
* [PATCH 06/12] readahead: context based method
2005-12-16 13:07 [PATCH 00/12] Adaptive read-ahead V10 Wu Fengguang
` (4 preceding siblings ...)
2005-12-16 13:07 ` [PATCH 05/12] readahead: state based method Wu Fengguang
@ 2005-12-16 13:07 ` Wu Fengguang
2005-12-16 13:07 ` [PATCH 07/12] readahead: other methods Wu Fengguang
` (5 subsequent siblings)
11 siblings, 0 replies; 15+ messages in thread
From: Wu Fengguang @ 2005-12-16 13:07 UTC (permalink / raw)
To: linux-kernel; +Cc: Andrew Morton, Wu Fengguang
[-- Attachment #1: readahead-method-context.patch --]
[-- Type: text/plain, Size: 10849 bytes --]
This is the slow code path.
No valid state info is available, so the page cache is queried to abtain the
required position/timing infomation.
Major steps:
- look back/forward to find the ra_index;
- look back to estimate a thrashing safe ra_size;
- assemble the next read-ahead request in file_ra_state;
- submit it.
Signed-off-by: Wu Fengguang <wfg@mail.ustc.edu.cn>
---
mm/readahead.c | 362 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
1 files changed, 362 insertions(+)
--- linux.orig/mm/readahead.c
+++ linux/mm/readahead.c
@@ -1166,6 +1166,368 @@ state_based_readahead(struct address_spa
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.
+ */
+
+#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
+ * __ 0
+ * _R PAGE_REFCNT_1
+ * A_ PAGE_REFCNT_2
+ * AR PAGE_REFCNT_3
+ *
+ * A/R: Active / Referenced
+ */
+static inline unsigned long page_refcnt(struct page *page)
+{
+ return page->flags & PAGE_REFCNT_MASK;
+}
+
+/*
+ * STATUS REFERENCE COUNT TYPE
+ * __ 0 not in inactive list
+ * __ 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 cold_page_refcnt(struct page *page)
+{
+ if (!page || PageActive(page))
+ return 0;
+
+ return page_refcnt(page);
+}
+
+static inline char page_refcnt_symbol(struct page *page)
+{
+ if (!page)
+ return 'X';
+ switch (page_refcnt(page)) {
+ case 0:
+ return '_';
+ case PAGE_REFCNT_1:
+ return '-';
+ case PAGE_REFCNT_2:
+ return '=';
+ case PAGE_REFCNT_3:
+ return '#';
+ }
+ return '?';
+}
+
+/*
+ * Count/estimate cache hits in range [first_index, last_index].
+ * The estimation is simple and optimistic.
+ */
+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;
+
+ read_lock_irq(&mapping->tree_lock);
+
+ /*
+ * 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 = __find_page(mapping, first_index +
+ size * ((i++ * 29) & 15) / 16);
+ if (cold_page_refcnt(page) >= PAGE_REFCNT_1 && ++count >= 2)
+ break;
+ }
+
+ read_unlock_irq(&mapping->tree_lock);
+
+ return size * count / i;
+}
+
+/*
+ * Look back and check history pages to estimate thrashing-threshold.
+ */
+static int query_page_cache(struct address_space *mapping,
+ struct file_ra_state *ra,
+ unsigned long *remain, pgoff_t offset,
+ unsigned long ra_min, unsigned long ra_max)
+{
+ int count;
+ pgoff_t index;
+ unsigned long nr_lookback;
+ struct radix_tree_cache cache;
+
+ /*
+ * Scan backward and check the near @ra_max pages.
+ * The count here determines ra_size.
+ */
+ read_lock_irq(&mapping->tree_lock);
+ index = radix_tree_lookup_head(&mapping->page_tree, offset, ra_max);
+ read_unlock_irq(&mapping->tree_lock);
+#ifdef DEBUG_READAHEAD_RADIXTREE
+ if (index <= offset) {
+ WARN_ON(!find_page(mapping, index));
+ if (index + ra_max > offset)
+ WARN_ON(find_page(mapping, index - 1));
+ } else {
+ BUG_ON(index > offset + 1);
+ WARN_ON(find_page(mapping, offset));
+ }
+#endif
+
+ *remain = offset - index + 1;
+
+ if (unlikely(*remain <= ra_min))
+ return ra_min;
+
+ if (!index)
+ return *remain;
+
+ if (offset + 1 == ra->readahead_index && ra_cache_hit_ok(ra))
+ count = *remain;
+ else if (count_cache_hit(mapping, index, offset) *
+ readahead_hit_rate >= *remain)
+ count = *remain;
+ else
+ return ra_min;
+
+ if (count < ra_max)
+ goto out;
+
+ /*
+ * Check the far pages coarsely.
+ * The big count here helps increase la_size.
+ */
+ nr_lookback = ra_max * (LOOKAHEAD_RATIO + 1) *
+ 100 / (readahead_ratio + 1);
+ if (nr_lookback > offset)
+ nr_lookback = offset;
+
+ radix_tree_cache_init(&cache);
+ read_lock_irq(&mapping->tree_lock);
+ for (count += ra_max; count < nr_lookback; count += ra_max) {
+ struct radix_tree_node *node;
+ node = radix_tree_cache_lookup_node(&mapping->page_tree,
+ &cache, offset - count, 1);
+ if (!node)
+ break;
+#ifdef DEBUG_READAHEAD_RADIXTREE
+ if (node != radix_tree_lookup_node(&mapping->page_tree,
+ offset - count, 1)) {
+ read_unlock_irq(&mapping->tree_lock);
+ printk(KERN_ERR "check radix_tree_cache_lookup_node!\n");
+ return 1;
+ }
+#endif
+ }
+ 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 process in adjust_rala_accelerated().
+ */
+ if (count >= offset)
+ return offset + 1;
+
+out:
+ count = count * readahead_ratio / 100;
+ return count;
+}
+
+/*
+ * Scan backward in the file for the first non-present page.
+ */
+static inline pgoff_t first_absent_page_bw(struct address_space *mapping,
+ pgoff_t index, unsigned long max_scan)
+{
+ struct radix_tree_cache cache;
+ struct page *page;
+ pgoff_t origin;
+
+ origin = index;
+ if (max_scan > index)
+ max_scan = index;
+
+ radix_tree_cache_init(&cache);
+ read_lock_irq(&mapping->tree_lock);
+ for (; origin - index <= max_scan;) {
+ page = radix_tree_cache_lookup(&mapping->page_tree,
+ &cache, --index);
+ if (page) {
+ index++;
+ break;
+ }
+ }
+ read_unlock_irq(&mapping->tree_lock);
+
+ return index;
+}
+
+/*
+ * Scan forward in the file for the first non-present page.
+ */
+static inline pgoff_t first_absent_page(struct address_space *mapping,
+ pgoff_t index, unsigned long max_scan)
+{
+ pgoff_t ra_index;
+
+ read_lock_irq(&mapping->tree_lock);
+ ra_index = radix_tree_lookup_tail(&mapping->page_tree,
+ index + 1, max_scan);
+ read_unlock_irq(&mapping->tree_lock);
+
+#ifdef DEBUG_READAHEAD_RADIXTREE
+ BUG_ON(ra_index <= index);
+ if (index + max_scan > index) {
+ if (ra_index <= index + max_scan)
+ WARN_ON(find_page(mapping, ra_index));
+ WARN_ON(!find_page(mapping, ra_index - 1));
+ }
+#endif
+
+ if (ra_index <= index + max_scan)
+ return ra_index;
+ else
+ return 0;
+}
+
+/*
+ * Determine the request parameters for context based read-ahead that extends
+ * from start of file.
+ *
+ * The major weakness of stateless method is perhaps the slow grow up speed 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
+ * half of which is safe. The added 'unsafe' half is the look-ahead part. It
+ * is expected to be safeguarded by rescue_pages() when the previous chunks are
+ * lost.
+ */
+static inline int adjust_rala_accelerated(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;
+
+ if (*ra_size > ra_max)
+ *ra_size = ra_max;
+ if (*la_size > *ra_size)
+ *la_size = *ra_size;
+
+ return 1;
+}
+
+/*
+ * Main function for page context based read-ahead.
+ */
+static inline 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_size,
+ unsigned long ra_min, unsigned long ra_max)
+{
+ pgoff_t ra_index;
+ 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 = first_absent_page(mapping, index, ra_max * 5 / 4);
+ if (unlikely(!ra_index))
+ return -1;
+ } else if (!prev_page) {
+ ra_index = first_absent_page_bw(mapping, index,
+ readahead_hit_rate + ra_min);
+ if (index - ra_index > readahead_hit_rate + ra_min)
+ return 0;
+ ra_min += 2 * (index - ra_index);
+ index = ra_index;
+ } else {
+ ra_index = index;
+ if (ra_has_index(ra, index))
+ ra_account(ra, RA_EVENT_READAHEAD_MUTILATE,
+ ra->readahead_index - index);
+ }
+
+ ra_size = query_page_cache(mapping, ra, &remain_pages,
+ index - 1, ra_min, ra_max);
+
+ la_size = ra_index - index;
+ if (remain_pages <= la_size && la_size > 1) {
+ rescue_pages(page, la_size);
+ return -1;
+ }
+
+ if (ra_size == index) {
+ if (!adjust_rala_accelerated(ra_max, &ra_size, &la_size))
+ return -1;
+ ra_set_class(ra, RA_CLASS_CONTEXT_ACCELERATED);
+ } else {
+ if (!adjust_rala(ra_max, &ra_size, &la_size))
+ return -1;
+ ra_set_class(ra, RA_CLASS_CONTEXT);
+ }
+
+ ra_set_index(ra, index, ra_index);
+ ra_set_size(ra, ra_size, la_size);
+
+ return 1;
+}
+
/*
* ra_size is mainly determined by:
--
^ permalink raw reply [flat|nested] 15+ messages in thread
* [PATCH 07/12] readahead: other methods
2005-12-16 13:07 [PATCH 00/12] Adaptive read-ahead V10 Wu Fengguang
` (5 preceding siblings ...)
2005-12-16 13:07 ` [PATCH 06/12] readahead: context " Wu Fengguang
@ 2005-12-16 13:07 ` Wu Fengguang
2005-12-16 13:07 ` [PATCH 08/12] readahead: events accounting Wu Fengguang
` (4 subsequent siblings)
11 siblings, 0 replies; 15+ messages in thread
From: Wu Fengguang @ 2005-12-16 13:07 UTC (permalink / raw)
To: linux-kernel; +Cc: Andrew Morton, Wu Fengguang
[-- Attachment #1: readahead-method-others.patch --]
[-- Type: text/plain, Size: 3590 bytes --]
Various read-ahead strategies for:
- fresh read from start of file
- backward prefetching
- seek and read one record pattern(db workload)
- quick recover from thrashing
Signed-off-by: Wu Fengguang <wfg@mail.ustc.edu.cn>
---
mm/readahead.c | 111 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
1 files changed, 111 insertions(+)
--- linux.orig/mm/readahead.c
+++ linux/mm/readahead.c
@@ -1528,6 +1528,117 @@ try_context_based_readahead(struct addre
return 1;
}
+/*
+ * Read-ahead on start of file.
+ *
+ * It is most important for small files.
+ * 1. Set a moderately large read-ahead size;
+ * 2. Issue the next read-ahead request as soon as possible.
+ *
+ * But be careful, there are some applications that dip into only the very head
+ * of a file. The most important thing is to prevent them from triggering the
+ * next (much larger) read-ahead request, which leads to lots of cache misses.
+ * Two pages should be enough for them, correct me if I'm wrong.
+ */
+static inline unsigned long
+newfile_readahead(struct address_space *mapping,
+ struct file *filp, struct file_ra_state *ra,
+ unsigned long req_size, unsigned long ra_min)
+{
+ unsigned long ra_size;
+ unsigned long la_size;
+
+ if (req_size > ra_min)
+ req_size = ra_min;
+
+ ra_size = 4 * req_size;
+ la_size = 2 * req_size;
+
+ ra_set_class(ra, RA_CLASS_NEWFILE);
+ 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 threshold estimation for stepping backward
+ * pattern: should be unnecessary.
+ */
+static inline int
+try_read_backward(struct file_ra_state *ra,
+ pgoff_t begin_index, pgoff_t end_index,
+ unsigned long ra_size,
+ unsigned long ra_min, unsigned long ra_max)
+{
+ if (ra_size > ra_max || end_index > ra->prev_page)
+ return 0;
+
+ if (ra_has_index(ra, ra->prev_page)) {
+ if (end_index > ra->la_index)
+ return 0;
+ ra_size += 2 * ra_cache_hit(ra, 0);
+ end_index = ra->la_index;
+ } else {
+ ra_size += readahead_hit_rate + ra_min;
+ end_index = ra->prev_page;
+ }
+
+ if (ra_size > ra_max)
+ ra_size = ra_max;
+
+ 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.
+ * Databases are known to have this seek-and-read-one-record pattern.
+ */
+static inline int
+try_random_readahead(struct file_ra_state *ra, pgoff_t index,
+ unsigned long ra_size, unsigned long ra_max)
+{
+ unsigned long hit0 = ra_cache_hit(ra, 0);
+ unsigned long hit1 = ra_cache_hit(ra, 1) + hit0;
+ unsigned long hit2 = ra_cache_hit(ra, 2);
+ unsigned long hit3 = ra_cache_hit(ra, 3);
+
+ if (!ra_has_index(ra, ra->prev_page))
+ return 0;
+
+ if (index == ra->prev_page + 1) { /* read after thrashing */
+ ra_size = hit0;
+ ra_set_class(ra, RA_CLASS_RANDOM_THRASHING);
+ ra_account(ra, RA_EVENT_READAHEAD_THRASHING,
+ ra->readahead_index - index);
+ } else if (ra_size < hit1 && /* read after seeking */
+ hit1 > hit2 / 2 &&
+ hit2 > hit3 / 2 &&
+ hit3 > hit1 / 2) {
+ ra_size = max(hit1, hit2);
+ ra_set_class(ra, RA_CLASS_RANDOM_SEEK);
+ } else
+ return 0;
+
+ if (ra_size > ra_max)
+ ra_size = ra_max;
+
+ ra_set_index(ra, index, index);
+ ra_set_size(ra, ra_size, 0);
+
+ return 1;
+}
/*
* ra_size is mainly determined by:
--
^ permalink raw reply [flat|nested] 15+ messages in thread
* [PATCH 08/12] readahead: events accounting
2005-12-16 13:07 [PATCH 00/12] Adaptive read-ahead V10 Wu Fengguang
` (6 preceding siblings ...)
2005-12-16 13:07 ` [PATCH 07/12] readahead: other methods Wu Fengguang
@ 2005-12-16 13:07 ` Wu Fengguang
2005-12-16 13:07 ` [PATCH 09/12] readahead: laptop mode support Wu Fengguang
` (3 subsequent siblings)
11 siblings, 0 replies; 15+ messages in thread
From: Wu Fengguang @ 2005-12-16 13:07 UTC (permalink / raw)
To: linux-kernel; +Cc: Andrew Morton, J?rn Engel, Ingo Oeser
[-- Attachment #1: readahead-account-events.patch --]
[-- Type: text/plain, Size: 11486 bytes --]
A debugfs file named `readahead/events' is created according to advices from
J?rn Engel, Andrew Morton and Ingo Oeser. It yields to much better
readability than the preious /proc/vmstat interface :)
It reveals various read-ahead activities/events, and is vital to the testing.
-------------------------------------------------------------------------
If you are experiencing performance problems, or want to help improve the
read-ahead logic, please send me the debug data. Thanks.
- Preparations
## Compile with CONFIG_DEBUG_FS('Kernel hacking ---> Debug Filesystem')
mkdir /debug
mount -t debug none /debug
- For each session with distinct access pattern
echo > /debug/readahead/events # reset the counters
# echo > /var/log/kern.log # you may want to backup it first
# echo 5 > /debug/readahead/debug_level # show verbose printk traces
## do one benchmark/task
# echo 0 > /debug/readahead/debug_level # revert to normal value
cp /debug/readahead/events readahead-events-`date +'%F_%R'`
# bzip2 -c /var/log/kern.log > kern.log-`date +'%F_%R'`.bz2
The commented out commands can uncover the very detailed file accesses,
which are useful sometimes. But the log file will be rather huge.
-------------------------------------------------------------------------
This is a trimmed down output on my PC:
# cat /debug/readahead/events
[table requests] total newfile state context none
cache_miss 403 56 12 69 263
read_random 260 37 5 17 201
io_congestion 0 0 0 0 0
io_cache_hit 85 0 24 46 0
io_block 9796 5613 822 143 3203
readahead 5956 5418 383 139 0
lookahead 961 650 212 98 0
lookahead_hit 449 181 164 58 41
lookahead_ignore 0 0 0 0 0
readahead_eof 4981 4768 171 28 0
readahead_shrink 0 0 0 0 0
readahead_thrash 0 0 0 0 0
readahead_mutilt 0 0 0 0 0
readahead_rescue 45 0 0 0 45
[table pages] total newfile state context none
cache_miss 5590 72 2506 181 2826
read_random 265 37 5 17 206
io_congestion 0 0 0 0 0
io_cache_hit 2440 0 1054 1366 0
io_block 165848 11117 147794 3668 3203
readahead 43080 11360 28949 2621 0
readahead_hit 38251 10716 25669 1818 9
lookahead 24013 1718 21641 647 0
lookahead_hit 20161 770 18679 712 0
lookahead_ignore 0 0 0 0 0
readahead_eof 15961 7924 7440 461 0
readahead_shrink 0 0 0 0 0
readahead_thrash 0 0 0 0 0
readahead_mutilt 0 0 0 0 0
readahead_rescue 240 0 0 0 240
[table summary] total newfile state context none
random_rate 4% 0% 1% 10% 99%
ra_hit_rate 88% 94% 88% 69% 900%
la_hit_rate 46% 27% 76% 58% 4100%
avg_ra_size 7 2 75 19 0
avg_la_size 25 3 102 7 0
Signed-off-by: Wu Fengguang <wfg@mail.ustc.edu.cn>
---
mm/readahead.c | 215 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
1 files changed, 213 insertions(+), 2 deletions(-)
--- linux.orig/mm/readahead.c
+++ linux/mm/readahead.c
@@ -108,6 +108,9 @@ enum ra_event {
u32 readahead_debug_level = 0;
u32 debug_disable_stateful_method = 0;
+static struct dentry *readahead_events_dentry;
+extern struct file_operations ra_debug_fops;
+
static int __init readahead_init(void)
{
struct dentry *root;
@@ -118,6 +121,9 @@ static int __init readahead_init(void)
debugfs_create_bool("disable_stateful_method", 0644, root,
&debug_disable_stateful_method);
+ readahead_events_dentry = debugfs_create_file("events",
+ 0644, root, NULL, &ra_debug_fops);
+
return 0;
}
@@ -135,6 +141,196 @@ static inline int disable_stateful_metho
return 0;
}
+#endif
+
+/*
+ * Read-ahead events accounting.
+ */
+#ifdef DEBUG_READAHEAD
+
+static const char * const ra_class_name[] = {
+ "total",
+ "newfile",
+ "state",
+ "context",
+ "contexta",
+ "backward",
+ "onthrash",
+ "onraseek",
+ "none",
+};
+
+static const char * const ra_event_name[] = {
+ "cache_miss",
+ "read_random",
+ "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_event_count[RA_CLASS_END+1][RA_EVENT_END+1][2];
+
+static inline void ra_account(struct file_ra_state *ra,
+ enum ra_event e, int pages)
+{
+ enum ra_class c;
+
+ if (e == RA_EVENT_READAHEAD_HIT && pages < 0) {
+ c = (ra->flags >> RA_CLASS_SHIFT) & RA_CLASS_MASK;
+ pages = -pages;
+ } else if (ra)
+ c = ra->flags & RA_CLASS_MASK;
+ else
+ c = RA_CLASS_END;
+
+ if (!c)
+ c = RA_CLASS_END;
+
+ ra_event_count[c][e][0] += 1;
+ ra_event_count[c][e][1] += pages;
+
+ if (e == RA_EVENT_READAHEAD)
+ ra_event_count[c][RA_EVENT_END][1] += pages * pages;
+}
+
+static int ra_account_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_END; e++) {
+ ra_event_count[0][e][i] = 0;
+ for (c = 1; c < RA_CLASS_END; c++)
+ ra_event_count[0][e][i] +=
+ ra_event_count[c][e][i];
+ }
+
+ seq_printf(s, event_fmt, table_name[i]);
+ for (c = 0; c <= RA_CLASS_END; c++)
+ seq_printf(s, class_fmt, ra_class_name[c]);
+ seq_puts(s, "\n");
+
+ for (e = 0; e < RA_EVENT_END; e++) {
+ 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_END; c++)
+ seq_printf(s, item_fmt,
+ ra_event_count[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_END; 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_END; c++)
+ seq_printf(s, percent_format,
+ (ra_event_count[c][RA_EVENT_READRANDOM][0] * 100) /
+ ((ra_event_count[c][RA_EVENT_READRANDOM][0] +
+ ra_event_count[c][RA_EVENT_READAHEAD][0]) | 1));
+ seq_puts(s, "\n");
+
+ seq_printf(s, event_fmt, "ra_hit_rate");
+ for (c = 0; c <= RA_CLASS_END; c++)
+ seq_printf(s, percent_format,
+ (ra_event_count[c][RA_EVENT_READAHEAD_HIT][1] * 100) /
+ (ra_event_count[c][RA_EVENT_READAHEAD][1] | 1));
+ seq_puts(s, "\n");
+
+ seq_printf(s, event_fmt, "la_hit_rate");
+ for (c = 0; c <= RA_CLASS_END; c++)
+ seq_printf(s, percent_format,
+ (ra_event_count[c][RA_EVENT_LOOKAHEAD_HIT][0] * 100) /
+ (ra_event_count[c][RA_EVENT_LOOKAHEAD][0] | 1));
+ seq_puts(s, "\n");
+
+ seq_printf(s, event_fmt, "var_ra_size");
+ for (c = 0; c <= RA_CLASS_END; c++)
+ seq_printf(s, item_fmt,
+ (ra_event_count[c][RA_EVENT_END][1] -
+ ra_event_count[c][RA_EVENT_READAHEAD][1] *
+ (ra_event_count[c][RA_EVENT_READAHEAD][1] /
+ (ra_event_count[c][RA_EVENT_READAHEAD][0] | 1))) /
+ (ra_event_count[c][RA_EVENT_READAHEAD][0] | 1));
+ seq_puts(s, "\n");
+
+ seq_printf(s, event_fmt, "avg_ra_size");
+ for (c = 0; c <= RA_CLASS_END; c++)
+ seq_printf(s, item_fmt,
+ (ra_event_count[c][RA_EVENT_READAHEAD][1] +
+ ra_event_count[c][RA_EVENT_READAHEAD][0] / 2) /
+ (ra_event_count[c][RA_EVENT_READAHEAD][0] | 1));
+ seq_puts(s, "\n");
+
+ seq_printf(s, event_fmt, "avg_la_size");
+ for (c = 0; c <= RA_CLASS_END; c++)
+ seq_printf(s, item_fmt,
+ (ra_event_count[c][RA_EVENT_LOOKAHEAD][1] +
+ ra_event_count[c][RA_EVENT_LOOKAHEAD][0] / 2) /
+ (ra_event_count[c][RA_EVENT_LOOKAHEAD][0] | 1));
+ seq_puts(s, "\n");
+
+ return 0;
+}
+
+static int ra_debug_open(struct inode *inode, struct file *file)
+{
+ return single_open(file, ra_account_show, NULL);
+}
+
+static ssize_t ra_debug_write(struct file *file, const char __user *buf,
+ size_t size, loff_t *offset)
+{
+ if (file->f_dentry == readahead_events_dentry)
+ memset(ra_event_count, 0, sizeof(ra_event_count));
+ return 1;
+}
+
+struct file_operations ra_debug_fops = {
+ .owner = THIS_MODULE,
+ .open = ra_debug_open,
+ .write = ra_debug_write,
+ .read = seq_read,
+ .llseek = seq_lseek,
+ .release = single_release,
+};
+
+#else /* !DEBUG_READAHEAD */
+
+static inline void ra_account(struct file_ra_state *ra,
+ enum ra_event e, int pages)
+{
+}
+
#endif /* DEBUG_READAHEAD */
@@ -472,6 +668,9 @@ int force_page_cache_readahead(struct ad
offset += this_chunk;
nr_to_read -= this_chunk;
}
+
+ ra_account(NULL, RA_EVENT_READAHEAD, ret);
+
return ret;
}
@@ -507,10 +706,16 @@ 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, 0);
+ ret = __do_page_cache_readahead(mapping, filp, offset, nr_to_read, 0);
+
+ ra_account(NULL, RA_EVENT_READAHEAD, ret);
+
+ return ret;
}
/*
@@ -532,6 +737,7 @@ blockable_page_cache_readahead(struct ad
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);
@@ -1013,6 +1219,8 @@ static int ra_dispatch(struct file_ra_st
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) {
@@ -1691,8 +1899,11 @@ page_cache_readahead_adaptive(struct add
if (page) {
if(!TestClearPageReadahead(page))
return 0;
- if (bdi_read_congested(mapping->backing_dev_info))
+ if (bdi_read_congested(mapping->backing_dev_info)) {
+ ra_account(ra, RA_EVENT_IO_CONGESTION,
+ end_index - index);
return 0;
+ }
}
if (page)
--
^ permalink raw reply [flat|nested] 15+ messages in thread
* [PATCH 09/12] readahead: laptop mode support
2005-12-16 13:07 [PATCH 00/12] Adaptive read-ahead V10 Wu Fengguang
` (7 preceding siblings ...)
2005-12-16 13:07 ` [PATCH 08/12] readahead: events accounting Wu Fengguang
@ 2005-12-16 13:07 ` Wu Fengguang
2005-12-16 13:07 ` [PATCH 10/12] readahead: disable look-ahead for loopback file Wu Fengguang
` (2 subsequent siblings)
11 siblings, 0 replies; 15+ messages in thread
From: Wu Fengguang @ 2005-12-16 13:07 UTC (permalink / raw)
To: linux-kernel; +Cc: Andrew Morton, Bart Samwel
[-- Attachment #1: readahead-laptop-mode.patch --]
[-- Type: text/plain, Size: 3223 bytes --]
When the laptop drive is spinned down, defer look-ahead to spin up time.
The implementation employs a poll based method, for performance is not a
concern in this code path. The poll interval is 64KB, which should be small
enough for movies/musics. The user space application is responsible for
proper caching to hide the spin-up-and-read delay.
------------------------------------------------------------------------
For crazy laptop users who prefer aggressive read-ahead, here is the way:
# echo 1000 > /proc/sys/vm/readahead_ratio
# blockdev --setra 524280 /dev/hda # this is the max possible value
Notes:
- It is still an untested feature.
- It is safer to use blockdev+fadvise to increase ra-max for a single file,
which needs patching your movie player.
- Be sure to restore them to sane values in normal operations!
Signed-off-by: Wu Fengguang <wfg@mail.ustc.edu.cn>
---
include/linux/writeback.h | 6 ++++++
mm/page-writeback.c | 2 +-
mm/readahead.c | 30 ++++++++++++++++++++++++++++++
3 files changed, 37 insertions(+), 1 deletion(-)
--- linux.orig/include/linux/writeback.h
+++ linux/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.orig/mm/page-writeback.c
+++ linux/mm/page-writeback.c
@@ -369,7 +369,7 @@ 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.orig/mm/readahead.c
+++ linux/mm/readahead.c
@@ -14,6 +14,7 @@
#include <linux/blkdev.h>
#include <linux/backing-dev.h>
#include <linux/pagevec.h>
+#include <linux/writeback.h>
/* The default max/min read-ahead pages. */
#define KB(size) (((size)*1024 + PAGE_CACHE_SIZE-1) / PAGE_CACHE_SIZE)
@@ -1035,6 +1036,30 @@ out:
}
/*
+ * Set a new look-ahead mark at @new_index.
+ * Return 0 if the new mark is successfully set.
+ */
+static inline 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 = find_page(mapping, new_index);
+ if (!page)
+ return 1;
+
+ SetPageReadahead(page);
+ if (ra->lookahead_index == index)
+ ra->lookahead_index = new_index;
+ return 0;
+}
+
+/*
* State based calculation of read-ahead request.
*
* This figure shows the meaning of file_ra_state members:
@@ -1904,6 +1929,11 @@ page_cache_readahead_adaptive(struct add
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)
--
^ permalink raw reply [flat|nested] 15+ messages in thread
* [PATCH 10/12] readahead: disable look-ahead for loopback file
2005-12-16 13:07 [PATCH 00/12] Adaptive read-ahead V10 Wu Fengguang
` (8 preceding siblings ...)
2005-12-16 13:07 ` [PATCH 09/12] readahead: laptop mode support Wu Fengguang
@ 2005-12-16 13:07 ` Wu Fengguang
2005-12-16 13:07 ` [PATCH 11/12] readahead: nfsd support Wu Fengguang
2005-12-16 13:07 ` [PATCH 12/12] readahead: improve interactivity Wu Fengguang
11 siblings, 0 replies; 15+ messages in thread
From: Wu Fengguang @ 2005-12-16 13:07 UTC (permalink / raw)
To: linux-kernel; +Cc: Andrew Morton, Wu Fengguang
[-- Attachment #1: readahead-disable-lookahead-for-loopback.patch --]
[-- Type: text/plain, Size: 1985 bytes --]
Loopback files normally contain filesystem, in which case there are already
proper look-aheads in the upper layer, more look-aheads on the loopback file
only ruins the read-ahead hit rate.
Signed-off-by: Wu Fengguang <wfg@mail.ustc.edu.cn>
---
I'd like to thank Tero Grundstr?m for uncovering the loopback problem.
drivers/block/loop.c | 6 ++++++
include/linux/fs.h | 1 +
mm/readahead.c | 7 +++++++
3 files changed, 14 insertions(+)
--- linux.orig/include/linux/fs.h
+++ linux/include/linux/fs.h
@@ -631,6 +631,7 @@ struct file_ra_state {
#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_MMAP (1UL<<31) /* mmaped page access */
+#define RA_FLAG_NO_LOOKAHEAD (1UL<<30) /* disable look-ahead */
struct file {
/*
--- linux.orig/drivers/block/loop.c
+++ linux/drivers/block/loop.c
@@ -782,6 +782,12 @@ 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.orig/mm/readahead.c
+++ linux/mm/readahead.c
@@ -1191,6 +1191,10 @@ static inline void ra_set_index(struct f
static inline void ra_set_size(struct file_ra_state *ra,
unsigned long ra_size, unsigned long la_size)
{
+ /* Disable look-ahead for loopback file. */
+ if (unlikely(ra->flags & RA_FLAG_NO_LOOKAHEAD))
+ la_size = 0;
+
ra->readahead_index = ra->ra_index + ra_size;
ra->lookahead_index = ra->readahead_index - la_size;
}
@@ -1571,6 +1575,9 @@ static int query_page_cache(struct addre
if (count < ra_max)
goto out;
+ if (unlikely(ra->flags & RA_FLAG_NO_LOOKAHEAD))
+ goto out;
+
/*
* Check the far pages coarsely.
* The big count here helps increase la_size.
--
^ permalink raw reply [flat|nested] 15+ messages in thread
* [PATCH 11/12] readahead: nfsd support
2005-12-16 13:07 [PATCH 00/12] Adaptive read-ahead V10 Wu Fengguang
` (9 preceding siblings ...)
2005-12-16 13:07 ` [PATCH 10/12] readahead: disable look-ahead for loopback file Wu Fengguang
@ 2005-12-16 13:07 ` Wu Fengguang
2005-12-17 0:05 ` Greg Banks
2005-12-16 13:07 ` [PATCH 12/12] readahead: improve interactivity Wu Fengguang
11 siblings, 1 reply; 15+ messages in thread
From: Wu Fengguang @ 2005-12-16 13:07 UTC (permalink / raw)
To: linux-kernel; +Cc: Andrew Morton, Neil Brown
[-- Attachment #1: readahead-nfsd-support.patch --]
[-- Type: text/plain, Size: 4880 bytes --]
- disable nfsd raparms: the new logic do not rely on it
- disable look-ahead on start of file: leave it to the client
For the case of NFS service, the new read-ahead logic
+ can handle disordered nfsd requests
+ can handle concurrent sequential requests on large files
with the help of look-ahead
- will have much ado about the concurrent ones on small files
------------------------------------------------------------------------
Notes about the concurrent nfsd requests issue:
nfsd read requests can be out of order, concurrent and with no ra-state info.
They are handled by the context based read-ahead method, which does the job
in the following steps:
1. scan in page cache
2. make read-ahead decisions
3. alloc new pages
4. insert new pages to page cache
A single read-ahead chunk in the client side will be dissembled and serviced
by many concurrent nfsd in the server side. It is highly possible for two or
more of these parallel nfsd instances to be in step 1/2/3 at the same time.
Without knowing others working on the same file region, they will issue
overlaped read-ahead requests, which lead to many conflicts at step 4.
There's no much luck to eliminate the concurrent problem in general and
efficient ways. But for small to medium NFS servers where the bottleneck
lies in storage devices, here is a performance tip:
# for pid in `pidof nfsd`; do taskset -p 1 $pid; done
This command effectively serializes all nfsd requests. It would be nice if
someone can code this serialization on a per-file basis.
------------------------------------------------------------------------
Here is some test output(8 nfsd; local mount with tcp,rsize=8192):
SERIALIZED, SMALL FILES
=======================
readahead_ratio = 0, ra_max = 128kb (old logic, the ra_max is really not relavant)
96.51s real 11.32s system 3.27s user 160334+2829 cs diff -r $NFSDIR $NFSDIR2
readahead_ratio = 70, ra_max = 1024kb (new read-ahead logic)
94.88s real 11.53s system 3.20s user 152415+3777 cs diff -r $NFSDIR $NFSDIR2
PARALLEL, SMALL FILES
=====================
readahead_ratio = 0, ra_max = 128kb
99.87s real 11.41s system 3.15s user 173945+9163 cs diff -r $NFSDIR $NFSDIR2
readahead_ratio = 70, ra_max = 1024kb
100.14s real 12.06s system 3.16s user 170865+13406 cs diff -r $NFSDIR $NFSDIR2
SERIALIZED, BIG FILES
=====================
readahead_ratio = 0, ra_max = 128kb
56.52s real 3.38s system 1.23s user 47930+5256 cs diff $NFSFILE $NFSFILE2
readahead_ratio = 70, ra_max = 1024kb
32.54s real 5.71s system 1.38s user 23851+17007 cs diff $NFSFILE $NFSFILE2
PARALLEL, BIG FILES
===================
readahead_ratio = 0, ra_max = 128kb
63.35s real 5.68s system 1.57s user 82594+48747 cs diff $NFSFILE $NFSFILE2
readahead_ratio = 70, ra_max = 1024kb
33.87s real 10.17s system 1.55s user 72291+100079 cs diff $NFSFILE $NFSFILE2
Signed-off-by: Wu Fengguang <wfg@mail.ustc.edu.cn>
---
fs/nfsd/vfs.c | 6 +++++-
include/linux/fs.h | 1 +
mm/readahead.c | 11 +++++++++--
3 files changed, 15 insertions(+), 3 deletions(-)
--- linux.orig/fs/nfsd/vfs.c
+++ linux/fs/nfsd/vfs.c
@@ -832,10 +832,14 @@ 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;
+ file->f_ra.flags |= RA_FLAG_NFSD;
if (file->f_op->sendfile) {
svc_pushback_unused_pages(rqstp);
--- linux.orig/include/linux/fs.h
+++ linux/include/linux/fs.h
@@ -632,6 +632,7 @@ struct file_ra_state {
#define RA_FLAG_INCACHE 0x02 /* file is already in cache */
#define RA_FLAG_MMAP (1UL<<31) /* mmaped page access */
#define RA_FLAG_NO_LOOKAHEAD (1UL<<30) /* disable look-ahead */
+#define RA_FLAG_NFSD (1UL<<29) /* request from nfsd */
struct file {
/*
--- linux.orig/mm/readahead.c
+++ linux/mm/readahead.c
@@ -15,11 +15,13 @@
#include <linux/backing-dev.h>
#include <linux/pagevec.h>
#include <linux/writeback.h>
+#include <linux/nfsd/const.h>
/* The default max/min read-ahead pages. */
#define KB(size) (((size)*1024 + PAGE_CACHE_SIZE-1) / PAGE_CACHE_SIZE)
#define MAX_RA_PAGES KB(VM_MAX_READAHEAD)
#define MIN_RA_PAGES KB(VM_MIN_READAHEAD)
+#define MIN_NFSD_PAGES KB(NFSSVC_MAXBLKSIZE/1024)
/* In laptop mode, poll delayed look-ahead on every ## pages read. */
#define LAPTOP_POLL_INTERVAL 16
@@ -1791,8 +1793,13 @@ newfile_readahead(struct address_space *
if (req_size > ra_min)
req_size = ra_min;
- ra_size = 4 * req_size;
- la_size = 2 * req_size;
+ if (unlikely(ra->flags & RA_FLAG_NFSD)) {
+ ra_size = MIN_NFSD_PAGES;
+ la_size = 0;
+ } else {
+ ra_size = 4 * req_size;
+ la_size = 2 * req_size;
+ }
ra_set_class(ra, RA_CLASS_NEWFILE);
ra_set_index(ra, 0, 0);
--
^ permalink raw reply [flat|nested] 15+ messages in thread
* [PATCH 12/12] readahead: improve interactivity
2005-12-16 13:07 [PATCH 00/12] Adaptive read-ahead V10 Wu Fengguang
` (10 preceding siblings ...)
2005-12-16 13:07 ` [PATCH 11/12] readahead: nfsd support Wu Fengguang
@ 2005-12-16 13:07 ` Wu Fengguang
11 siblings, 0 replies; 15+ messages in thread
From: Wu Fengguang @ 2005-12-16 13:07 UTC (permalink / raw)
To: linux-kernel; +Cc: Andrew Morton, Con Kolivas
[-- Attachment #1: readahead-low-latency.patch --]
[-- Type: text/plain, Size: 4263 bytes --]
Since the VM_MAX_READAHEAD is greatly enlarged and the algorithm become more
complex, it may be necessary to insert some cond_resched() calls in the
read-ahead path.
----------------------------------------------------------------------------
If you feel more latency with the new read-ahead code, the cause can
either be the complex read-ahead code, or some low level routines not ready
to support the larger default 1M read-ahead size. It can be cleared out with
the following commands:
dd if=/dev/zero of=sparse bs=1M seek=10000 count=1
cp sparse /dev/null
If the above copy does not lead to audio jitters, then it's an low level
issue. There are basicly two ways:
1) compile kernel with CONFIG_PREEMPT_VOLUNTARY/CONFIG_PREEMPT
2) reduce the read-ahead request size by
blockdev --setra 256 /dev/hda # or whatever device you are using
Signed-off-by: Wu Fengguang <wfg@mail.ustc.edu.cn>
---
This is recommended by Con Kolivas to improve respond time for desktop.
Thanks!
fs/mpage.c | 4 +++-
mm/readahead.c | 14 +++++++++++++-
2 files changed, 16 insertions(+), 2 deletions(-)
--- linux.orig/mm/readahead.c
+++ linux/mm/readahead.c
@@ -496,8 +496,10 @@ 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)) {
__pagevec_lru_add(&lru_pvec);
+ cond_resched();
+ }
continue;
} /* else fall through to release */
}
@@ -617,6 +619,7 @@ __do_page_cache_readahead(struct address
}
read_unlock_irq(&mapping->tree_lock);
+ cond_resched();
page = page_cache_alloc_cold(mapping);
read_lock_irq(&mapping->tree_lock);
if (!page)
@@ -1025,6 +1028,7 @@ static int rescue_pages(struct page *pag
spin_unlock_irq(&zone->lru_lock);
+ cond_resched();
page = find_page(mapping, index);
if (!page)
goto out;
@@ -1099,6 +1103,7 @@ static unsigned long node_readahead_agin
unsigned long sum = 0;
cpumask_t mask = node_to_cpumask(numa_node_id());
+ cond_resched();
for_each_cpu_mask(cpu, mask)
sum += per_cpu(readahead_aging, cpu);
@@ -1213,6 +1218,7 @@ static int ra_dispatch(struct file_ra_st
int actual;
enum ra_class ra_class;
+ cond_resched();
ra_class = (ra->flags & RA_CLASS_MASK);
BUG_ON(ra_class == 0 || ra_class > RA_CLASS_END);
@@ -1235,6 +1241,7 @@ static int ra_dispatch(struct file_ra_st
actual = __do_page_cache_readahead(mapping, filp,
ra->ra_index, ra_size, la_size);
+ cond_resched();
#ifdef READAHEAD_NONBLOCK
if (actual < ra_size) {
@@ -1507,6 +1514,7 @@ static int count_cache_hit(struct addres
int count = 0;
int i;
+ cond_resched();
read_lock_irq(&mapping->tree_lock);
/*
@@ -1544,6 +1552,7 @@ static int query_page_cache(struct addre
* 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_lookup_head(&mapping->page_tree, offset, ra_max);
read_unlock_irq(&mapping->tree_lock);
@@ -1589,6 +1598,7 @@ static int query_page_cache(struct addre
if (nr_lookback > offset)
nr_lookback = offset;
+ cond_resched();
radix_tree_cache_init(&cache);
read_lock_irq(&mapping->tree_lock);
for (count += ra_max; count < nr_lookback; count += ra_max) {
@@ -1635,6 +1645,7 @@ static inline pgoff_t first_absent_page_
if (max_scan > index)
max_scan = index;
+ cond_resched();
radix_tree_cache_init(&cache);
read_lock_irq(&mapping->tree_lock);
for (; origin - index <= max_scan;) {
@@ -1658,6 +1669,7 @@ static inline pgoff_t first_absent_page(
{
pgoff_t ra_index;
+ cond_resched();
read_lock_irq(&mapping->tree_lock);
ra_index = radix_tree_lookup_tail(&mapping->page_tree,
index + 1, max_scan);
--- linux.orig/fs/mpage.c
+++ linux/fs/mpage.c
@@ -343,8 +343,10 @@ mpage_readpages(struct address_space *ma
bio = do_mpage_readpage(bio, page,
nr_pages - page_idx,
&last_block_in_bio, get_block);
- if (!pagevec_add(&lru_pvec, page))
+ if (!pagevec_add(&lru_pvec, page)) {
__pagevec_lru_add(&lru_pvec);
+ cond_resched();
+ }
} else {
page_cache_release(page);
}
--
^ permalink raw reply [flat|nested] 15+ messages in thread
* Re: [PATCH 11/12] readahead: nfsd support
2005-12-16 13:07 ` [PATCH 11/12] readahead: nfsd support Wu Fengguang
@ 2005-12-17 0:05 ` Greg Banks
2005-12-17 13:35 ` Wu Fengguang
0 siblings, 1 reply; 15+ messages in thread
From: Greg Banks @ 2005-12-17 0:05 UTC (permalink / raw)
To: Wu Fengguang; +Cc: linux-kernel, Andrew Morton, Neil Brown
On Fri, Dec 16, 2005 at 09:07:49PM +0800, Wu Fengguang wrote:
> ------------------------------------------------------------------------
> Here is some test output(8 nfsd; local mount with tcp,rsize=8192):
What are the numbers when you use a more realistic rsize like 32768?
Greg.
--
Greg Banks, R&D Software Engineer, SGI Australian Software Group.
I don't speak for SGI.
^ permalink raw reply [flat|nested] 15+ messages in thread
* Re: [PATCH 11/12] readahead: nfsd support
2005-12-17 0:05 ` Greg Banks
@ 2005-12-17 13:35 ` Wu Fengguang
0 siblings, 0 replies; 15+ messages in thread
From: Wu Fengguang @ 2005-12-17 13:35 UTC (permalink / raw)
To: Greg Banks; +Cc: linux-kernel, Andrew Morton, Neil Brown
On Sat, Dec 17, 2005 at 11:05:22AM +1100, Greg Banks wrote:
> On Fri, Dec 16, 2005 at 09:07:49PM +0800, Wu Fengguang wrote:
> > ------------------------------------------------------------------------
> > Here is some test output(8 nfsd; local mount with tcp,rsize=8192):
>
> What are the numbers when you use a more realistic rsize like 32768?
Here they are. The normal data are now much better, and come close to that of
the serialized ones.
NORMAL
readahead_ratio = 8, ra_max = 1024kb (old logic)
48.36s real 2.22s system 1.51s user 7209+4110 cs diff $NFSFILE $NFSFILE2
readahead_ratio = 70, ra_max = 1024kb (new logic)
30.04s real 2.46s system 1.33s user 5420+2492 cs diff $NFSFILE $NFSFILE2
readahead_ratio = 8, ra_max = 1024kb
92.99s real 10.32s system 3.23s user 145004+1826 cs diff -r $NFSDIR $NFSDIR2 > /dev/null
readahead_ratio = 70, ra_max = 1024kb
90.96s real 10.68s system 3.22s user 144414+2520 cs diff -r $NFSDIR $NFSDIR2 > /dev/null
SERIALIZED
readahead_ratio = 8, ra_max = 1024kb
47.58s real 2.10s system 1.27s user 7933+1357 cs diff $NFSFILE $NFSFILE2
readahead_ratio = 70, ra_max = 1024kb
29.46s real 2.41s system 1.38s user 5590+2613 cs diff $NFSFILE $NFSFILE2
readahead_ratio = 8, ra_max = 1024kb
93.02s real 10.67s system 3.25s user 144850+2286 cs diff -r $NFSDIR $NFSDIR2 > /dev/null
readahead_ratio = 70, ra_max = 1024kb
91.15s real 11.04s system 3.31s user 144432+2814 cs diff -r $NFSDIR $NFSDIR2 > /dev/null
Regards,
Wu
^ permalink raw reply [flat|nested] 15+ messages in thread
end of thread, other threads:[~2005-12-17 13:11 UTC | newest]
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2005-12-16 13:07 [PATCH 00/12] Adaptive read-ahead V10 Wu Fengguang
2005-12-16 13:07 ` [PATCH 01/12] radixtree: look-aside cache Wu Fengguang
2005-12-16 13:07 ` [PATCH 02/12] readahead: some preparation Wu Fengguang
2005-12-16 13:07 ` [PATCH 03/12] readahead: call scheme Wu Fengguang
2005-12-16 13:07 ` [PATCH 04/12] readahead: parameters Wu Fengguang
2005-12-16 13:07 ` [PATCH 05/12] readahead: state based method Wu Fengguang
2005-12-16 13:07 ` [PATCH 06/12] readahead: context " Wu Fengguang
2005-12-16 13:07 ` [PATCH 07/12] readahead: other methods Wu Fengguang
2005-12-16 13:07 ` [PATCH 08/12] readahead: events accounting Wu Fengguang
2005-12-16 13:07 ` [PATCH 09/12] readahead: laptop mode support Wu Fengguang
2005-12-16 13:07 ` [PATCH 10/12] readahead: disable look-ahead for loopback file Wu Fengguang
2005-12-16 13:07 ` [PATCH 11/12] readahead: nfsd support Wu Fengguang
2005-12-17 0:05 ` Greg Banks
2005-12-17 13:35 ` Wu Fengguang
2005-12-16 13:07 ` [PATCH 12/12] readahead: improve interactivity Wu Fengguang
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