The patch titled
readahead: rescue_pages()
has been added to the -mm tree. Its filename is
readahead-rescue_pages.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: rescue_pages()
From: Wu Fengguang <wfg@xxxxxxxxxxxxxxxx>
Introduce function rescue_pages() to protect pages in danger of thrashing.
Signed-off-by: Wu Fengguang <wfg@xxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxx>
---
mm/readahead.c | 90 +++++++++++++++++++++++++++++++++++++++++++++++
1 files changed, 90 insertions(+)
diff -puN mm/readahead.c~readahead-rescue_pages mm/readahead.c
--- a/mm/readahead.c~readahead-rescue_pages
+++ a/mm/readahead.c
@@ -673,6 +673,96 @@ 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
+
+/*
+ * Move pages in danger (of thrashing) to the head of inactive_list.
+ * Not expected to happen frequently.
+ *
+ * @page will be skipped: it's grabbed and won't die away.
+ * The following @nr_pages-1 pages will be protected.
+ */
+static unsigned long rescue_pages(struct page *page, unsigned long nr_pages)
+{
+ int pgrescue = 0;
+ pgoff_t index = page_index(page);
+ struct address_space *mapping = page_mapping(page);
+ struct page *grabbed_page = NULL;
+ struct zone *zone;
+
+ dprintk("rescue_pages(ino=%lu, index=%lu nr=%lu)\n",
+ mapping->host->i_ino, index, nr_pages);
+
+ for(;;) {
+ zone = page_zone(page);
+ spin_lock_irq(&zone->lru_lock);
+
+ if (!PageLRU(page))
+ goto out_unlock;
+
+ while (page_mapping(page) == mapping &&
+ page_index(page) == index) {
+ struct page *the_page = page;
+ page = list_entry((page)->lru.prev, struct page, lru);
+ if (!PageActive(the_page) &&
+ !PageLocked(the_page) &&
+ page_count(the_page) == 1) {
+ list_move(&the_page->lru, &zone->inactive_list);
+ pgrescue++;
+ }
+ index++;
+ if (!--nr_pages)
+ goto out_unlock;
+ }
+
+ spin_unlock_irq(&zone->lru_lock);
+ cond_resched();
+
+ if (grabbed_page)
+ page_cache_release(grabbed_page);
+ grabbed_page = page = find_get_page(mapping, index);
+ if (!page)
+ goto out;
+ }
+
+out_unlock:
+ spin_unlock_irq(&zone->lru_lock);
+out:
+ if (grabbed_page)
+ page_cache_release(grabbed_page);
+ ra_account(NULL, RA_EVENT_READAHEAD_RESCUE, pgrescue);
+ return nr_pages;
+}
+
+#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-introduce-scan-hole-data-functions.patch
mm-introduce-probe_page.patch
mm-introduce-pg_readahead.patch
readahead-add-look-ahead-support-to-__do_page_cache_readahead.patch
readahead-insert-cond_resched-calls.patch
readahead-minmax_ra_pages.patch
readahead-events-accounting.patch
readahead-rescue_pages.patch
readahead-sysctl-parameters.patch
readahead-min-max-sizes.patch
readahead-state-based-method-aging-accounting.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-user-recommended-size.patch
readahead-initial-method.patch
readahead-backward-prefetching-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-remove-size-limit-on-read_ahead_kb.patch
readahead-remove-size-limit-of-max_sectors_kb-on-read_ahead_kb.patch
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