[RFC 3/3] non-resident page tracking

Rik van Riel
2005-08-08T20:14:19Z

[-- Attachment #1: useonce-cleanup --]
[-- Type: text/plain, Size: 5740 bytes --]

Simplify the use-once code. I have not benchmarked this change yet,
but I expect it to have little impact on most workloads. It gets rid
of some magic code though, which is nice.

Signed-off-by: Rik van Riel <riel@surriel.com>

Index: linux-2.6.12-vm/include/linux/page-flags.h
===================================================================
--- linux-2.6.12-vm.orig/include/linux/page-flags.h
+++ linux-2.6.12-vm/include/linux/page-flags.h
@@ -75,7 +75,9 @@
#define PG_mappedtodisk 17 /* Has blocks allocated on-disk */
#define PG_reclaim 18 /* To be reclaimed asap */
#define PG_nosave_free 19 /* Free, should not be written */
+
#define PG_uncached 20 /* Page has been mapped as uncached */
+#define PG_new 21 /* Newly allocated page */

/*
* Global page accounting. One instance per CPU. Only unsigned longs are
@@ -306,6 +308,11 @@ extern void __mod_page_state(unsigned of
#define SetPageUncached(page) set_bit(PG_uncached, &(page)->flags)
#define ClearPageUncached(page) clear_bit(PG_uncached, &(page)->flags)

+#define PageNew(page) test_bit(PG_new, &(page)->flags)
+#define SetPageNew(page) set_bit(PG_new, &(page)->flags)
+#define ClearPageNew(page) clear_bit(PG_new, &(page)->flags)
+#define TestClearPageNew(page) test_and_clear_bit(PG_new, &(page)->flags)
+
struct page; /* forward declaration */

int test_clear_page_dirty(struct page *page);
Index: linux-2.6.12-vm/mm/filemap.c
===================================================================
--- linux-2.6.12-vm.orig/mm/filemap.c
+++ linux-2.6.12-vm/mm/filemap.c
@@ -383,6 +383,7 @@ int add_to_page_cache(struct page *page,
if (!error) {
page_cache_get(page);
SetPageLocked(page);
+ SetPageNew(page);
page->mapping = mapping;
page->index = offset;
mapping->nrpages++;
@@ -727,7 +728,6 @@ void do_generic_mapping_read(struct addr
unsigned long offset;
unsigned long last_index;
unsigned long next_index;
- unsigned long prev_index;
loff_t isize;
struct page *cached_page;
int error;
@@ -736,7 +736,6 @@ void do_generic_mapping_read(struct addr
cached_page = NULL;
index = *ppos >> PAGE_CACHE_SHIFT;
next_index = index;
- prev_index = ra.prev_page;
last_index = (*ppos + desc->count + PAGE_CACHE_SIZE-1) >> PAGE_CACHE_SHIFT;
offset = *ppos & ~PAGE_CACHE_MASK;

@@ -783,13 +782,7 @@ page_ok:
if (mapping_writably_mapped(mapping))
flush_dcache_page(page);

- /*
- * When (part of) the same page is read multiple times
- * in succession, only mark it as accessed the first time.
- */
- if (prev_index != index)
- mark_page_accessed(page);
- prev_index = index;
+ mark_page_accessed(page);

/*
* Ok, we have the page, and it's up-to-date, so
Index: linux-2.6.12-vm/mm/shmem.c
===================================================================
--- linux-2.6.12-vm.orig/mm/shmem.c
+++ linux-2.6.12-vm/mm/shmem.c
@@ -1525,11 +1525,8 @@ static void do_shmem_file_read(struct fi
*/
if (mapping_writably_mapped(mapping))
flush_dcache_page(page);
- /*
- * Mark the page accessed if we read the beginning.
- */
- if (!offset)
- mark_page_accessed(page);
+
+ mark_page_accessed(page);
} else
page = ZERO_PAGE(0);

Index: linux-2.6.12-vm/mm/swap.c
===================================================================
--- linux-2.6.12-vm.orig/mm/swap.c
+++ linux-2.6.12-vm/mm/swap.c
@@ -115,19 +115,11 @@ void fastcall activate_page(struct page

/*
* Mark a page as having seen activity.
- *
- * inactive,unreferenced -> inactive,referenced
- * inactive,referenced -> active,unreferenced
- * active,unreferenced -> active,referenced
*/
void fastcall mark_page_accessed(struct page *page)
{
- if (!PageActive(page) && PageReferenced(page) && PageLRU(page)) {
- activate_page(page);
- ClearPageReferenced(page);
- } else if (!PageReferenced(page)) {
+ if (!PageReferenced(page))
SetPageReferenced(page);
- }
}

EXPORT_SYMBOL(mark_page_accessed);
@@ -157,6 +149,7 @@ void fastcall lru_cache_add_active(struc
if (!pagevec_add(pvec, page))
__pagevec_lru_add_active(pvec);
put_cpu_var(lru_add_active_pvecs);
+ ClearPageNew(page);
}

void lru_add_drain(void)
Index: linux-2.6.12-vm/mm/vmscan.c
===================================================================
--- linux-2.6.12-vm.orig/mm/vmscan.c
+++ linux-2.6.12-vm/mm/vmscan.c
@@ -225,27 +225,6 @@ static int shrink_slab(unsigned long sca
return 0;
}

-/* Called without lock on whether page is mapped, so answer is unstable */
-static inline int page_mapping_inuse(struct page *page)
-{
- struct address_space *mapping;
-
- /* Page is in somebody's page tables. */
- if (page_mapped(page))
- return 1;
-
- /* Be more reluctant to reclaim swapcache than pagecache */
- if (PageSwapCache(page))
- return 1;
-
- mapping = page_mapping(page);
- if (!mapping)
- return 0;
-
- /* File is mmap'd by somebody? */
- return mapping_mapped(mapping);
-}
-
static inline int is_page_cache_freeable(struct page *page)
{
return page_count(page) - !!PagePrivate(page) == 2;
@@ -398,9 +377,13 @@ static int shrink_list(struct list_head
goto keep_locked;

referenced = page_referenced(page, 1, sc->priority <= 0);
- /* In active use or really unfreeable? Activate it. */
- if (referenced && page_mapping_inuse(page))
+
+ if (referenced) {
+ /* New page. Wait and see if it gets used again... */
+ if (TestClearPageNew(page))
+ goto keep_locked;
goto activate_locked;
+ }

#ifdef CONFIG_SWAP
/*