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 <[email protected]>
---
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);
}
--