On Apr 14, 2010, at 9:11 PM, KOSAKI Motohiro wrote:
Now, vmscan pageout() is one of IO throuput degression source.
Some IO workload makes very much order-0 allocation and reclaim
and pageout's 4K IOs are making annoying lots seeks.
At least, kswapd can avoid such pageout() because kswapd don't
need to consider OOM-Killer situation. that's no risk.
Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
What's your opinion on trying to cluster the writes done by pageout,
instead of not doing any paging out in kswapd?
Something along these lines:
Cluster writes to disk due to memory pressure.
Write out logically adjacent pages to the one we're paging out
so that we may get better IOs in these situations:
These pages are likely to be contiguous on disk to the one we're
writing out, so they should get merged into a single disk IO.
Signed-off-by: Suleiman Souhlal <suleiman@xxxxxxxxxx>
diff --git a/mm/vmscan.c b/mm/vmscan.c
index c26986c..4e5a613 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -48,6 +48,8 @@
#include "internal.h"
+#define PAGEOUT_CLUSTER_PAGES 16
+
struct scan_control {
/* Incremented by the number of inactive pages that were scanned */
unsigned long nr_scanned;
@@ -350,6 +352,8 @@ typedef enum {
static pageout_t pageout(struct page *page, struct address_space
*mapping,
enum pageout_io sync_writeback)
{
+ int i;
+
/*
* If the page is dirty, only perform writeback if that write
* will be non-blocking. To prevent this allocation from being
@@ -408,6 +412,37 @@ static pageout_t pageout(struct page *page,
struct address_space *mapping,
}
/*
+ * Try to write out logically adjacent dirty pages too, if
+ * possible, to get better IOs, as the IO scheduler should
+ * merge them with the original one, if the file is not too
+ * fragmented.
+ */
+ for (i = 1; i < PAGEOUT_CLUSTER_PAGES; i++) {
+ struct page *p2;
+ int err;
+
+ p2 = find_get_page(mapping, page->index + i);
+ if (p2) {
+ if (trylock_page(p2) == 0) {
+ page_cache_release(p2);
+ break;
+ }
+ if (page_mapped(p2))
+ try_to_unmap(p2, 0);
+ if (PageDirty(p2)) {
+ err = write_one_page(p2, 0);
+ page_cache_release(p2);
+ if (err)
+ break;
+ } else {
+ unlock_page(p2);
+ page_cache_release(p2);
+ break;
+ }
+ }
+ }
+
+ /*
* Wait on writeback if requested to. This happens when
* direct reclaiming a large contiguous area and the
* first attempt to free a range of pages fails.
--
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