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SubjectRe: Possible dcache BUG


On Tue, 10 Aug 2004, Linus Torvalds wrote:
>
> So I suspect it's a balancing issue. Possibly just the slight change in
> slab balancing to fix the highmem problems. Maybe we shrink slab _too_
> aggressively or something.

Udo, that's a simple thing to check. If it's the slab balancing changes,
then you should be able to test it with just a

bk cset -x1.1830.4.3

if you have the current BK and are a BK user, or by just revertign the
patch here ("patch -R -p1" from inside your linux source tree) if you're
not a BK user..

Linus

-----
# This is a BitKeeper generated diff -Nru style patch.
#
# ChangeSet
# 2004/07/31 14:47:41-07:00 akpm@osdl.org
# [PATCH] slab memory shrinking balancing fix
#
# The logic in shrink_slab tries to balance the proportion of slab which it
# scans against the proportion of pagecache which the caller scanned. Problem
# is that with a large number of highmem LRU pages and a small number of lowmem
# LRU pages, the amount of pagecache scanning appears to be very small, so we
# don't push slab hard enough.
#
# The patch changes things so that for, say, a GFP_KERNEL allocation attempt we
# only consider ZONE_NORMAL and ZONE_DMA when calculating "what proportion of
# the LRU did the caller just scan".
#
# This will have the effect of shrinking slab harder in response to GFP_KERNEL
# allocations than for GFP_HIGHMEM allocations.
#
# Signed-off-by: Andrew Morton <akpm@osdl.org>
# Signed-off-by: Linus Torvalds <torvalds@osdl.org>
#
# mm/vmscan.c
# 2004/07/31 14:35:31-07:00 akpm@osdl.org +23 -9
# slab memory shrinking balancing fix
#
# mm/page_alloc.c
# 2004/07/31 14:02:21-07:00 akpm@osdl.org +0 -11
# slab memory shrinking balancing fix
#
# include/linux/mm.h
# 2004/07/31 14:02:26-07:00 akpm@osdl.org +0 -2
# slab memory shrinking balancing fix
#
diff -Nru a/include/linux/mm.h b/include/linux/mm.h
--- a/include/linux/mm.h 2004-08-10 22:15:23 -07:00
+++ b/include/linux/mm.h 2004-08-10 22:15:23 -07:00
@@ -706,8 +706,6 @@

extern struct vm_area_struct *find_extend_vma(struct mm_struct *mm, unsigned long addr);

-extern unsigned int nr_used_zone_pages(void);
-
extern struct page * vmalloc_to_page(void *addr);
extern struct page * follow_page(struct mm_struct *mm, unsigned long address,
int write);
diff -Nru a/mm/page_alloc.c b/mm/page_alloc.c
--- a/mm/page_alloc.c 2004-08-10 22:15:23 -07:00
+++ b/mm/page_alloc.c 2004-08-10 22:15:23 -07:00
@@ -825,17 +825,6 @@

EXPORT_SYMBOL(nr_free_pages);

-unsigned int nr_used_zone_pages(void)
-{
- unsigned int pages = 0;
- struct zone *zone;
-
- for_each_zone(zone)
- pages += zone->nr_active + zone->nr_inactive;
-
- return pages;
-}
-
#ifdef CONFIG_NUMA
unsigned int nr_free_pages_pgdat(pg_data_t *pgdat)
{
diff -Nru a/mm/vmscan.c b/mm/vmscan.c
--- a/mm/vmscan.c 2004-08-10 22:15:23 -07:00
+++ b/mm/vmscan.c 2004-08-10 22:15:23 -07:00
@@ -169,22 +169,25 @@
* slab to avoid swapping.
*
* We do weird things to avoid (scanned*seeks*entries) overflowing 32 bits.
+ *
+ * `lru_pages' represents the number of on-LRU pages in all the zones which
+ * are eligible for the caller's allocation attempt. It is used for balancing
+ * slab reclaim versus page reclaim.
*/
-static int shrink_slab(unsigned long scanned, unsigned int gfp_mask)
+static int shrink_slab(unsigned long scanned, unsigned int gfp_mask,
+ unsigned long lru_pages)
{
struct shrinker *shrinker;
- long pages;

if (down_trylock(&shrinker_sem))
return 0;

- pages = nr_used_zone_pages();
list_for_each_entry(shrinker, &shrinker_list, list) {
unsigned long long delta;

delta = (4 * scanned) / shrinker->seeks;
delta *= (*shrinker->shrinker)(0, gfp_mask);
- do_div(delta, pages + 1);
+ do_div(delta, lru_pages + 1);
shrinker->nr += delta;
if (shrinker->nr < 0)
shrinker->nr = LONG_MAX; /* It wrapped! */
@@ -896,6 +899,7 @@
int total_scanned = 0, total_reclaimed = 0;
struct reclaim_state *reclaim_state = current->reclaim_state;
struct scan_control sc;
+ unsigned long lru_pages = 0;
int i;

sc.gfp_mask = gfp_mask;
@@ -903,8 +907,12 @@

inc_page_state(allocstall);

- for (i = 0; zones[i] != 0; i++)
- zones[i]->temp_priority = DEF_PRIORITY;
+ for (i = 0; zones[i] != NULL; i++) {
+ struct zone *zone = zones[i];
+
+ zone->temp_priority = DEF_PRIORITY;
+ lru_pages += zone->nr_active + zone->nr_inactive;
+ }

for (priority = DEF_PRIORITY; priority >= 0; priority--) {
sc.nr_mapped = read_page_state(nr_mapped);
@@ -912,7 +920,7 @@
sc.nr_reclaimed = 0;
sc.priority = priority;
shrink_caches(zones, &sc);
- shrink_slab(sc.nr_scanned, gfp_mask);
+ shrink_slab(sc.nr_scanned, gfp_mask, lru_pages);
if (reclaim_state) {
sc.nr_reclaimed += reclaim_state->reclaimed_slab;
reclaim_state->reclaimed_slab = 0;
@@ -997,7 +1005,7 @@
for (priority = DEF_PRIORITY; priority >= 0; priority--) {
int all_zones_ok = 1;
int end_zone = 0; /* Inclusive. 0 = ZONE_DMA */
-
+ unsigned long lru_pages = 0;

if (nr_pages == 0) {
/*
@@ -1021,6 +1029,12 @@
end_zone = pgdat->nr_zones - 1;
}
scan:
+ for (i = 0; i <= end_zone; i++) {
+ struct zone *zone = pgdat->node_zones + i;
+
+ lru_pages += zone->nr_active + zone->nr_inactive;
+ }
+
/*
* Now scan the zone in the dma->highmem direction, stopping
* at the last zone which needs scanning.
@@ -1048,7 +1062,7 @@
sc.priority = priority;
shrink_zone(zone, &sc);
reclaim_state->reclaimed_slab = 0;
- shrink_slab(sc.nr_scanned, GFP_KERNEL);
+ shrink_slab(sc.nr_scanned, GFP_KERNEL, lru_pages);
sc.nr_reclaimed += reclaim_state->reclaimed_slab;
total_reclaimed += sc.nr_reclaimed;
if (zone->all_unreclaimable)
-
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