On Mon, 7 Dec 1998 18:01:31 GMT, "Stephen C. Tweedie" <sct@redhat.com>
said:
>> what we really need is somebody to try it out on 4M and
>> 8M machines...
> Been doing that. 2.1.130 is the fastest kernel ever in 8MB (using
> defrag builds over NFS as a benchmark): 25% faster that 2.0.36. 2.1.131
> is consistently about 10% slower at the same job than 130 (but still
> faster than 2.0 ever was).
Right: 2.1.131 + Rik's fixes + my fix to Rik's fixes (see below) has set
a new record for my 8MB benchmarks. In 64MB, it is behaving much more
rationally than older kernels: still very very very fast, especially
interactively, but with no massive cache growth and swap storms when
doing filesystem intensive operations, and swap throughput when we _do_
swap is great.
I've changed your readahead stuff to look like:
struct page *page_map = lookup_swap_cache(entry);
if (!page_map) {
swapin_readahead(entry);
page_map = read_swap_cache(entry);
}
which is the right way to do it: we don't want to start a readahead on a
swap hit, because that will try to extend the readahead "zone" one page
at a time as we hit existing pages in the cache. That ends up with
one-page writes, with terrible performance if we have other IO activity
on the same disk. I also tuned the readahead down to 8 pages, for the
tests on 8MB: we can make this tunable later.
I also fixed the readahead logic itself to start with the correct
initial page (previously you were doing a "++i" in the for () condition,
which means we were skipping the first page in the readahead). Now that
the readahead is being submitted before we do the wait-for-page, we need
to make absolutely sure to include the required page in the readahead
set.
Finally, I'll experiment with making the readahead a granularity-based
thing, so that we read an aligned block of (say) 64k from swap at a
time. By starting the readahead on such a boundary rather than at the
current page, we can page in entire regions of swap very rapidly given a
random pattern of page hits.
For now, this is looking very good indeed.
--Stephen
----------------------------------------------------------------
--- include/linux/swap.h.~1~ Mon Dec 7 12:05:54 1998
+++ include/linux/swap.h Mon Dec 7 18:55:55 1998
@@ -90,6 +90,7 @@
extern struct page * read_swap_cache_async(unsigned long, int);
#define read_swap_cache(entry) read_swap_cache_async(entry, 1);
extern int FASTCALL(swap_count(unsigned long));
+extern struct page * lookup_swap_cache(unsigned long);
/*
* Make these inline later once they are working properly.
*/
--- mm/page_alloc.c.~1~ Fri Nov 27 12:36:42 1998
+++ mm/page_alloc.c Mon Dec 7 20:42:36 1998
@@ -360,6 +360,35 @@
}
/*
+ * Primitive swap readahead code. We simply read the
+ * next 8 entries in the swap area. This method is
+ * chosen because it doesn't cost us any seek time.
+ * We also make sure to queue the 'original' request
+ * together with the readahead ones...
+ */
+void swapin_readahead(unsigned long entry) {
+ int i;
+ struct page *new_page;
+ unsigned long offset = SWP_OFFSET(entry);
+ struct swap_info_struct *swapdev = SWP_TYPE(entry) + swap_info;
+
+ for (i = 0; i < 8; i++) {
+ if (offset >= swapdev->max
+ || nr_free_pages - atomic_read(&nr_async_pages) <
+ (freepages.high + freepages.low)/2)
+ return;
+ if (!swapdev->swap_map[offset] ||
+ test_bit(offset, swapdev->swap_lockmap))
+ continue;
+ new_page = read_swap_cache_async(SWP_ENTRY(SWP_TYPE(entry), offset), 0);
+ if (new_page != NULL)
+ __free_page(new_page);
+ offset++;
+ }
+ return;
+}
+
+/*
* The tests may look silly, but it essentially makes sure that
* no other process did a swap-in on us just as we were waiting.
*
@@ -370,10 +399,12 @@
pte_t * page_table, unsigned long entry, int write_access)
{
unsigned long page;
- struct page *page_map;
-
- page_map = read_swap_cache(entry);
+ struct page *page_map = lookup_swap_cache(entry);
+ if (!page_map) {
+ swapin_readahead(entry);
+ page_map = read_swap_cache(entry);
+ }
if (pte_val(*page_table) != entry) {
if (page_map)
free_page_and_swap_cache(page_address(page_map));
--- mm/page_io.c.~1~ Fri Nov 27 12:36:42 1998
+++ mm/page_io.c Mon Dec 7 18:55:55 1998
@@ -60,7 +60,7 @@
}
/* Don't allow too many pending pages in flight.. */
- if (atomic_read(&nr_async_pages) > SWAP_CLUSTER_MAX)
+ if (atomic_read(&nr_async_pages) > pager_daemon.swap_cluster)
wait = 1;
p = &swap_info[type];
--- mm/swap.c.~1~ Mon Dec 7 12:05:54 1998
+++ mm/swap.c Mon Dec 7 18:55:55 1998
@@ -61,14 +61,14 @@
swapstat_t swapstats = {0};
buffer_mem_t buffer_mem = {
- 5, /* minimum percent buffer */
- 10, /* borrow percent buffer */
+ 1, /* minimum percent buffer */
+ 20, /* borrow percent buffer */
60 /* maximum percent buffer */
};
buffer_mem_t page_cache = {
- 5, /* minimum percent page cache */
- 15, /* borrow percent page cache */
+ 1, /* minimum percent page cache */
+ 30, /* borrow percent page cache */
75 /* maximum */
};
--- mm/swap_state.c.~1~ Fri Nov 27 12:36:42 1998
+++ mm/swap_state.c Mon Dec 7 18:55:55 1998
@@ -258,9 +258,10 @@
* incremented.
*/
-static struct page * lookup_swap_cache(unsigned long entry)
+struct page * lookup_swap_cache(unsigned long entry)
{
struct page *found;
+ swap_cache_find_total++;
while (1) {
found = find_page(&swapper_inode, entry);
@@ -268,8 +269,10 @@
return 0;
if (found->inode != &swapper_inode || !PageSwapCache(found))
goto out_bad;
- if (!PageLocked(found))
+ if (!PageLocked(found)) {
+ swap_cache_find_success++;
return found;
+ }
__free_page(found);
__wait_on_page(found);
}
--- mm/vmscan.c.~1~ Mon Dec 7 12:05:54 1998
+++ mm/vmscan.c Mon Dec 7 18:55:55 1998
@@ -432,6 +432,8 @@
if (buffer_over_borrow() || pgcache_over_borrow())
state = 0;
+ if (atomic_read(&nr_async_pages) > pager_daemon.swap_cluster / 2)
+ shrink_mmap(i, gfp_mask);
switch (state) {
do {
-
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