[PATCH 2/4] lumpy cleanup a missplaced comment and simplify some code

Andy Whitcroft
2006-12-06T17:00:44Z

lumpy: cleanup a missplaced comment and simplify some code

Move the comment for isolate_lru_pages() back to its function
and comment the new function. Add some running commentry on the
area scan. Cleanup the indentation on switch to match the majority
view in mm/*. Finally, clarify the boundary pfn calculations.

Signed-off-by: Andy Whitcroft <apw@shadowen.org>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
---
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 0f2d961..0effa3e 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -606,21 +606,14 @@ keep:
}

/*
- * zone->lru_lock is heavily contended. Some of the functions that
- * shrink the lists perform better by taking out a batch of pages
- * and working on them outside the LRU lock.
+ * Attempt to remove the specified page from its LRU. Only take this
+ * page if it is of the appropriate PageActive status. Pages which
+ * are being freed elsewhere are also ignored.
*
- * For pagecache intensive workloads, this function is the hottest
- * spot in the kernel (apart from copy_*_user functions).
- *
- * Appropriate locks must be held before calling this function.
+ * @page: page to consider
+ * @active: active/inactive flag only take pages of this type
*
- * @nr_to_scan: The number of pages to look through on the list.
- * @src: The LRU list to pull pages off.
- * @dst: The temp list to put pages on to.
- * @scanned: The number of pages that were scanned.
- *
- * returns how many pages were moved onto *@dst.
+ * returns 0 on success, -ve errno on failure.
*/
int __isolate_lru_page(struct page *page, int active)
{
@@ -642,6 +635,23 @@ int __isolate_lru_page(struct page *page, int active)
return ret;
}

+/*
+ * zone->lru_lock is heavily contended. Some of the functions that
+ * shrink the lists perform better by taking out a batch of pages
+ * and working on them outside the LRU lock.
+ *
+ * For pagecache intensive workloads, this function is the hottest
+ * spot in the kernel (apart from copy_*_user functions).
+ *
+ * Appropriate locks must be held before calling this function.
+ *
+ * @nr_to_scan: The number of pages to look through on the list.
+ * @src: The LRU list to pull pages off.
+ * @dst: The temp list to put pages on to.
+ * @scanned: The number of pages that were scanned.
+ *
+ * returns how many pages were moved onto *@dst.
+ */
static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
struct list_head *src, struct list_head *dst,
unsigned long *scanned, int order)
@@ -659,26 +669,31 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,

active = PageActive(page);
switch (__isolate_lru_page(page, active)) {
- case 0:
- list_move(&page->lru, dst);
- nr_taken++;
- break;
+ case 0:
+ list_move(&page->lru, dst);
+ nr_taken++;
+ break;

- case -EBUSY:
- /* else it is being freed elsewhere */
- list_move(&page->lru, src);
- continue;
+ case -EBUSY:
+ /* else it is being freed elsewhere */
+ list_move(&page->lru, src);
+ continue;

- default:
- BUG();
+ default:
+ BUG();
}

if (!order)
continue;

- page_pfn = pfn = __page_to_pfn(page);
- end_pfn = pfn &= ~((1 << order) - 1);
- end_pfn += 1 << order;
+ /*
+ * Attempt to take all pages in the order aligned region
+ * surrounding the tag page. Only take those pages of
+ * the same active state as that tag page.
+ */
+ page_pfn = __page_to_pfn(page);
+ pfn = page_pfn & ~((1 << order) - 1);
+ end_pfn = pfn + (1 << order);
for (; pfn < end_pfn; pfn++) {
if (unlikely(pfn == page_pfn))
continue;
@@ -688,17 +703,16 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
scan++;
tmp = __pfn_to_page(pfn);
switch (__isolate_lru_page(tmp, active)) {
- case 0:
- list_move(&tmp->lru, dst);
- nr_taken++;
- continue;
-
- case -EBUSY:
- /* else it is being freed elsewhere */
- list_move(&tmp->lru, src);
- default:
- break;
+ case 0:
+ list_move(&tmp->lru, dst);
+ nr_taken++;
+ continue;

+ case -EBUSY:
+ /* else it is being freed elsewhere */
+ list_move(&tmp->lru, src);
+ default:
+ break;
}
break;
}