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Subject[PATCH 07/23] readahead: insert cond_resched() calls
Since the VM_MAX_READAHEAD is greatly enlarged and the algorithm become more
complex, it becomes necessary to insert some cond_resched() calls in the
read-ahead path.

If desktop users still feel audio jitters with the new read-ahead code,
please try one of the following ways to get rid of it:

1) compile kernel with CONFIG_PREEMPT_VOLUNTARY/CONFIG_PREEMPT
2) reduce the read-ahead request size by running
blockdev --setra 256 /dev/hda # or whatever device you are using

Signed-off-by: Wu Fengguang <wfg@mail.ustc.edu.cn>
---

This patch is recommended by Con Kolivas to improve respond time for desktop.
Thanks!

fs/mpage.c | 4 +++-
mm/readahead.c | 9 +++++++--
2 files changed, 10 insertions(+), 3 deletions(-)
--- linux-2.6.16-rc6-mm2.orig/mm/readahead.c
+++ linux-2.6.16-rc6-mm2/mm/readahead.c
@@ -145,8 +145,10 @@ int read_cache_pages(struct address_spac
continue;
}
ret = filler(data, page);
- if (!pagevec_add(&lru_pvec, page))
+ if (!pagevec_add(&lru_pvec, page)) {
+ cond_resched();
__pagevec_lru_add(&lru_pvec);
+ }
if (ret) {
while (!list_empty(pages)) {
struct page *victim;
@@ -184,8 +186,10 @@ static int read_pages(struct address_spa
page->index, GFP_KERNEL)) {
ret = mapping->a_ops->readpage(filp, page);
if (ret != AOP_TRUNCATED_PAGE) {
- if (!pagevec_add(&lru_pvec, page))
+ if (!pagevec_add(&lru_pvec, page)) {
+ cond_resched();
__pagevec_lru_add(&lru_pvec);
+ }
continue;
} /* else fall through to release */
}
@@ -299,6 +303,7 @@ __do_page_cache_readahead(struct address
continue;

read_unlock_irq(&mapping->tree_lock);
+ cond_resched();
page = page_cache_alloc_cold(mapping);
read_lock_irq(&mapping->tree_lock);
if (!page)
--- linux-2.6.16-rc6-mm2.orig/fs/mpage.c
+++ linux-2.6.16-rc6-mm2/fs/mpage.c
@@ -407,8 +407,10 @@ mpage_readpages(struct address_space *ma
&last_block_in_bio, &map_bh,
&first_logical_block,
get_block);
- if (!pagevec_add(&lru_pvec, page))
+ if (!pagevec_add(&lru_pvec, page)) {
+ cond_resched();
__pagevec_lru_add(&lru_pvec);
+ }
} else {
page_cache_release(page);
}
--
-
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