The patch titled
readahead: support functions
has been added to the -mm tree. Its filename is
readahead-support-functions.patch
See http://www.zip.com.au/~akpm/linux/patches/stuff/added-to-mm.txt to find
out what to do about this
------------------------------------------------------
Subject: readahead: support functions
From: Wu Fengguang <wfg@xxxxxxxxxxxxxxxx>
Several support functions of adaptive read-ahead.
Signed-off-by: Wu Fengguang <wfg@xxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxx>
---
include/linux/mm.h | 11 ++++
mm/readahead.c | 107 +++++++++++++++++++++++++++++++++++++++++++
2 files changed, 118 insertions(+)
diff -puN include/linux/mm.h~readahead-support-functions include/linux/mm.h
--- 25/include/linux/mm.h~readahead-support-functions Wed May 24 16:49:20 2006
+++ 25-akpm/include/linux/mm.h Wed May 24 16:49:20 2006
@@ -988,6 +988,17 @@ 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_ADAPTIVE_READAHEAD
+extern int readahead_ratio;
+#else
+#define readahead_ratio 1
+#endif /* CONFIG_ADAPTIVE_READAHEAD */
+
+static inline int prefer_adaptive_readahead(void)
+{
+ return readahead_ratio >= 10;
+}
+
/* Do stack extension */
extern int expand_stack(struct vm_area_struct *vma, unsigned long address);
#ifdef CONFIG_IA64
diff -puN mm/readahead.c~readahead-support-functions mm/readahead.c
--- 25/mm/readahead.c~readahead-support-functions Wed May 24 16:49:20 2006
+++ 25-akpm/mm/readahead.c Wed May 24 16:49:20 2006
@@ -682,6 +682,113 @@ unsigned long max_sane_readahead(unsigne
}
/*
+ * Adaptive read-ahead.
+ *
+ * Good read patterns are compact both in space and time. The read-ahead logic
+ * tries to grant larger read-ahead size to better readers under the constraint
+ * of system memory and load pressure.
+ *
+ * It employs two methods to estimate the max thrashing safe read-ahead size:
+ * 1. state based - the default one
+ * 2. context based - the failsafe one
+ * The integration of the dual methods has the merit of being agile and robust.
+ * It makes the overall design clean: special cases are handled in general by
+ * the stateless method, leaving the stateful one simple and fast.
+ *
+ * To improve throughput and decrease read delay, the logic 'looks ahead'.
+ * In most read-ahead chunks, one page will be selected and tagged with
+ * PG_readahead. Later when the page with PG_readahead is read, the logic
+ * will be notified to submit the next read-ahead chunk in advance.
+ *
+ * a read-ahead chunk
+ * +-----------------------------------------+
+ * | # PG_readahead |
+ * +-----------------------------------------+
+ * ^ When this page is read, notify me for the next read-ahead.
+ *
+ */
+
+#ifdef CONFIG_ADAPTIVE_READAHEAD
+
+/*
+ * The nature of read-ahead allows false tests to occur occasionally.
+ * 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);
+ return page;
+}
+
+/*
+ * Move pages in danger (of thrashing) to the head of inactive_list.
+ * Not expected to happen frequently.
+ */
+static unsigned long rescue_pages(struct page *page, unsigned long nr_pages)
+{
+ int pgrescue;
+ pgoff_t index;
+ struct zone *zone;
+ struct address_space *mapping;
+
+ 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);
+
+ cond_resched();
+ 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;
+}
+
+#endif /* CONFIG_ADAPTIVE_READAHEAD */
+
+/*
* Read-ahead events accounting.
*/
#ifdef CONFIG_DEBUG_READAHEAD
_
Patches currently in -mm which might be from wfg@xxxxxxxxxxxxxxxx are
readahead-kconfig-options.patch
radixtree-look-aside-cache.patch
radixtree-hole-scanning-functions.patch
readahead-page-flag-pg_readahead.patch
readahead-refactor-do_generic_mapping_read.patch
readahead-refactor-__do_page_cache_readahead.patch
readahead-insert-cond_resched-calls.patch
readahead-common-macros.patch
readahead-events-accounting.patch
readahead-support-functions.patch
readahead-sysctl-parameters.patch
readahead-min-max-sizes.patch
readahead-state-based-method-aging-accounting.patch
readahead-state-based-method-data-structure.patch
readahead-state-based-method-routines.patch
readahead-state-based-method.patch
readahead-context-based-method.patch
readahead-initial-method-guiding-sizes.patch
readahead-initial-method-thrashing-guard-size.patch
readahead-initial-method-expected-read-size.patch
readahead-initial-method-user-recommended-size.patch
readahead-initial-method.patch
readahead-backward-prefetching-method.patch
readahead-seeking-reads-method.patch
readahead-thrashing-recovery-method.patch
readahead-call-scheme.patch
readahead-laptop-mode.patch
readahead-loop-case.patch
readahead-nfsd-case.patch
readahead-turn-on-by-default.patch
readahead-debug-radix-tree-new-functions.patch
readahead-debug-traces-showing-accessed-file-names.patch
readahead-debug-traces-showing-read-patterns.patch
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