Pages which are under writeout to swap are locked, and not
PageWriteback(). So page allocators do not throttle against them in
shrink_caches().
This causes enormous list scans and general coma under really heavy
swapout loads.
One fix would be to teach shrink_cache() to wait on PG_locked for swap
pages. The other approach is to set both PG_locked and PG_writeback
for swap pages so they can be handled in the same manner as file-backed
pages in shrink_cache().
This patch takes the latter approach.
=====================================
--- 2.5.18/fs/buffer.c~swap-writeback Sat May 25 23:26:46 2002
+++ 2.5.18-akpm/fs/buffer.c Sun May 26 00:50:20 2002
@@ -544,6 +544,14 @@ static void end_buffer_async_read(struct
*/
if (page_uptodate && !PageError(page))
SetPageUptodate(page);
+
+ /*
+ * swap page handling is a bit hacky. A standalone completion handler
+ * for swapout pages would fix that up. swapin can use this function.
+ */
+ if (PageSwapCache(page) && PageWriteback(page))
+ end_page_writeback(page);
+
unlock_page(page);
return;
@@ -2271,6 +2279,9 @@ int brw_kiovec(int rw, int nr, struct ki
* calls block_flushpage() under spinlock and hits a locked buffer, and
* schedules under spinlock. Another approach would be to teach
* find_trylock_page() to also trylock the page's writeback flags.
+ *
+ * Swap pages are also marked PageWriteback when they are being written
+ * so that memory allocators will throttle on them.
*/
int brw_page(int rw, struct page *page,
struct block_device *bdev, sector_t b[], int size)
@@ -2301,6 +2312,11 @@ int brw_page(int rw, struct page *page,
bh = bh->b_this_page;
} while (bh != head);
+ if (rw == WRITE) {
+ BUG_ON(PageWriteback(page));
+ SetPageWriteback(page);
+ }
+
/* Stage 2: start the IO */
do {
struct buffer_head *next = bh->b_this_page;
--- 2.5.18/mm/swap_state.c~swap-writeback Sat May 25 23:26:46 2002
+++ 2.5.18-akpm/mm/swap_state.c Sun May 26 00:50:19 2002
@@ -36,10 +36,8 @@ static int swap_writepage(struct page *p
* swapper_space doesn't have a real inode, so it gets a special vm_writeback()
* so we don't need swap special cases in generic_vm_writeback().
*
- * FIXME: swap pages are locked, but not PageWriteback while under writeout.
- * This will confuse throttling in shrink_cache(). It may be advantageous to
- * set PG_writeback against swap pages while they're also locked. Either that,
- * or special-case swap pages in shrink_cache().
+ * Swap pages are PageLocked and PageWriteback while under writeout so that
+ * memory allocators will throttle against them.
*/
static int swap_vm_writeback(struct page *page, int *nr_to_write)
{
-
-
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This archive was generated by hypermail 2b29 : Fri May 31 2002 - 22:00:18 EST