Re: kswapd eating too much CPU on ac16/ac18

Mike Galbraith
2000-06-16T05:45:33Z

On Wed, 14 Jun 2000, Alan Cox wrote:

> > ac4 was faster than ever, it looked like it wasn't swapping at all
> >
> > ac16 and ac18 are both awful, dpkg takes an infinite time, all of it dominated
>
> Im interested to know if ac9/ac10 is the slow->fast change point

ac5 is definately the breaking point. ac5 doesn't survive make -j30..
starts swinging it's VM machette at everything in sight. Reversing the
VM changes to ac4 restores throughput to test1 levels (11 minute build
vs 21-26 minutes for everything forward).

Exact tested reversals below. FWIW, page aging doesn't seem to be the
problem. I disabled that in ac17 and saw zero difference. (What may or
not be a hint is that the /* Let shrink_mmap handle this swapout. */ bit
in vmscan.c does make a consistent difference. Reverting that bit alone
takes a minimum of 4 minutes off build time)

-Mike

diff -urN linux-2.4.0-ac4/include/linux/mm.h linux-2.4.0-ac5/include/linux/mm.h
--- linux-2.4.0-ac4/include/linux/mm.h Fri Jun 16 06:09:48 2000
+++ linux-2.4.0-ac5/include/linux/mm.h Fri Jun 16 06:17:29 2000
@@ -153,6 +153,7 @@
struct buffer_head * buffers;
unsigned long virtual; /* nonzero if kmapped */
struct zone_struct *zone;
+ unsigned int age;
} mem_map_t;

#define get_page(p) atomic_inc(&(p)->count)
@@ -169,7 +170,7 @@
#define PG_dirty 4
#define PG_decr_after 5
#define PG_unused_01 6
-#define PG__unused_02 7
+#define PG_active 7
#define PG_slab 8
#define PG_swap_cache 9
#define PG_skip 10
@@ -185,6 +186,7 @@
#define ClearPageUptodate(page) clear_bit(PG_uptodate, &(page)->flags)
#define PageDirty(page) test_bit(PG_dirty, &(page)->flags)
#define SetPageDirty(page) set_bit(PG_dirty, &(page)->flags)
+#define ClearPageDirty(page) clear_bit(PG_dirty, &(page)->flags)
#define PageLocked(page) test_bit(PG_locked, &(page)->flags)
#define LockPage(page) set_bit(PG_locked, &(page)->flags)
#define TryLockPage(page) test_and_set_bit(PG_locked, &(page)->flags)
@@ -192,6 +194,9 @@
clear_bit(PG_locked, &(page)->flags); \
wake_up(&page->wait); \
} while (0)
+#define PageActive(page) test_bit(PG_active, &(page)->flags)
+#define SetPageActive(page) set_bit(PG_active, &(page)->flags)
+#define ClearPageActive(page) clear_bit(PG_active, &(page)->flags)
#define PageError(page) test_bit(PG_error, &(page)->flags)
#define SetPageError(page) set_bit(PG_error, &(page)->flags)
#define ClearPageError(page) clear_bit(PG_error, &(page)->flags)
diff -urN linux-2.4.0-ac4/include/linux/swap.h linux-2.4.0-ac5/include/linux/swap.h
--- linux-2.4.0-ac4/include/linux/swap.h Wed Jun 14 11:52:13 2000
+++ linux-2.4.0-ac5/include/linux/swap.h Fri Jun 16 06:17:30 2000
@@ -168,12 +168,15 @@
spin_lock(&pagemap_lru_lock); \
list_add(&(page)->lru, &lru_cache); \
nr_lru_pages++; \
+ page->age = 2; \
+ SetPageActive(page); \
spin_unlock(&pagemap_lru_lock); \
} while (0)

#define __lru_cache_del(page) \
do { \
list_del(&(page)->lru); \
+ ClearPageActive(page); \
nr_lru_pages--; \
} while (0)

diff -urN linux-2.4.0-ac4/mm/filemap.c linux-2.4.0-ac5/mm/filemap.c
--- linux-2.4.0-ac4/mm/filemap.c Wed May 24 06:23:09 2000
+++ linux-2.4.0-ac5/mm/filemap.c Fri Jun 16 06:15:32 2000
@@ -264,7 +264,16 @@
page = list_entry(page_lru, struct page, lru);
list_del(page_lru);

- if (PageTestandClearReferenced(page))
+ if (PageTestandClearReferenced(page)) {
+ page->age += 3;
+ if (page->age > 10)
+ page->age = 10;
+ goto dispose_continue;
+ }
+ if (page->age)
+ page->age--;
+
+ if (page->age)
goto dispose_continue;

count--;
@@ -317,28 +326,34 @@
goto cache_unlock_continue;

/*
+ * Page is from a zone we don't care about.
+ * Don't drop page cache entries in vain.
+ */
+ if (page->zone->free_pages > page->zone->pages_high)
+ goto cache_unlock_continue;
+
+ /*
* Is it a page swap page? If so, we want to
* drop it if it is no longer used, even if it
* were to be marked referenced..
*/
if (PageSwapCache(page)) {
- spin_unlock(&pagecache_lock);
- __delete_from_swap_cache(page);
- goto made_inode_progress;
- }
-
- /*
- * Page is from a zone we don't care about.
- * Don't drop page cache entries in vain.
- */
- if (page->zone->free_pages > page->zone->pages_high)
+ if (!PageDirty(page)) {
+ spin_unlock(&pagecache_lock);
+ __delete_from_swap_cache(page);
+ goto made_inode_progress;
+ }
+ /* PageDeferswap -> we swap out the page now. */
+ if (gfp_mask & __GFP_IO)
+ goto async_swap;
goto cache_unlock_continue;
+ }

/* is it a page-cache page? */
if (page->mapping) {
if (!PageDirty(page) && !pgcache_under_min()) {
- __remove_inode_page(page);
spin_unlock(&pagecache_lock);
+ __remove_inode_page(page);
goto made_inode_progress;
}
goto cache_unlock_continue;
@@ -351,6 +366,14 @@
unlock_continue:
spin_lock(&pagemap_lru_lock);
UnlockPage(page);
+ page_cache_release(page);
+ goto dispose_continue;
+async_swap:
+ spin_unlock(&pagecache_lock);
+ /* Do NOT unlock the page ... that is done after IO. */
+ ClearPageDirty(page);
+ rw_swap_page(WRITE, page, 0);
+ spin_lock(&pagemap_lru_lock);
page_cache_release(page);
dispose_continue:
list_add(page_lru, &lru_cache);
diff -urN linux-2.4.0-ac4/mm/page_alloc.c linux-2.4.0-ac5/mm/page_alloc.c
--- linux-2.4.0-ac4/mm/page_alloc.c Sat May 13 07:12:42 2000
+++ linux-2.4.0-ac5/mm/page_alloc.c Fri Jun 16 06:15:32 2000
@@ -93,6 +93,8 @@
BUG();
if (PageDecrAfter(page))
BUG();
+ if (PageDirty(page))
+ BUG();

zone = page->zone;

diff -urN linux-2.4.0-ac4/mm/swap_state.c linux-2.4.0-ac5/mm/swap_state.c
--- linux-2.4.0-ac4/mm/swap_state.c Wed May 24 06:23:09 2000
+++ linux-2.4.0-ac5/mm/swap_state.c Fri Jun 16 06:15:32 2000
@@ -73,6 +73,7 @@
PAGE_BUG(page);

PageClearSwapCache(page);
+ ClearPageDirty(page);
remove_inode_page(page);
}

diff -urN linux-2.4.0-ac4/mm/vmscan.c linux-2.4.0-ac5/mm/vmscan.c
--- linux-2.4.0-ac4/mm/vmscan.c Wed May 24 06:23:09 2000
+++ linux-2.4.0-ac5/mm/vmscan.c Fri Jun 16 06:15:32 2000
@@ -62,6 +62,10 @@
goto out_failed;
}

+ /* Can only do this if we age all active pages. */
+ if (PageActive(page) && page->age > 1)
+ goto out_failed;
+
if (TryLockPage(page))
goto out_failed;

@@ -74,6 +78,8 @@
* memory, and we should just continue our scan.
*/
if (PageSwapCache(page)) {
+ if (pte_dirty(pte))
+ SetPageDirty(page);
entry.val = page->index;
swap_duplicate(entry);
set_pte(page_table, swp_entry_to_pte(entry));
@@ -181,7 +187,10 @@
vmlist_access_unlock(vma->vm_mm);

/* OK, do a physical asynchronous write to swap. */
- rw_swap_page(WRITE, page, 0);
+ // rw_swap_page(WRITE, page, 0);
+ /* Let shrink_mmap handle this swapout. */
+ SetPageDirty(page);
+ UnlockPage(page);

out_free_success:
page_cache_release(page);