Re: [PATCH 19/21] swap_prefetch: Conversion of nr_unstable to ZVC

Con Kolivas
2006-06-12T23:43:34Z

On Tuesday 13 June 2006 07:14, Christoph Lameter wrote:
> Subject: swap_prefetch: conversion of nr_unstable to per zone counter
> From: Christoph Lameter <clameter@sgi.com>
>
> The determination of the vm state is now not that expensive
> anymore after we remove the use of the page state.
> Remove the logic to avoid the expensive checks.
>
> Signed-off-by: Christoph Lameter <clameter@sgi.com>
> Signed-off-by: Andrew Morton <akpm@osdl.org>

Nack. You're changing some other code unintentionally.

>
> Index: linux-2.6.17-rc6-cl/mm/swap_prefetch.c
> ===================================================================
> --- linux-2.6.17-rc6-cl.orig/mm/swap_prefetch.c 2006-06-12
> 12:55:39.368358636 -0700 +++
> linux-2.6.17-rc6-cl/mm/swap_prefetch.c 2006-06-12 12:55:41.321362692 -0700
> @@ -298,7 +298,7 @@ static int prefetch_suitable(void)
> {
> unsigned long limit;
> struct zone *z;
> - int node, ret = 0, test_pagestate = 0;
> + int node, ret = 0;
>
> /* Purposefully racy */
> if (test_bit(0, &swapped.busy)) {
> @@ -306,19 +306,6 @@ static int prefetch_suitable(void)
> goto out;
> }
>
> - /*
> - * get_page_state and above_background_load are expensive so we only
> - * perform them every SWAP_CLUSTER_MAX prefetched_pages.
> - * We test to see if we're above_background_load as disk activity
> - * even at low priority can cause interrupt induced scheduling
> - * latencies.
> - */
> - if (!(sp_stat.prefetched_pages % SWAP_CLUSTER_MAX)) {
> - if (above_background_load())
> - goto out;

We still need the above_background_load check, just remove the test_pagestate
check and it can be checked every time. Drop the comment about get_page_state
only.

> - test_pagestate = 1;
> - }
> -
> clear_current_prefetch_free();
>
> /*
> @@ -357,7 +344,6 @@ static int prefetch_suitable(void)
> */
> for_each_node_mask(node, sp_stat.prefetch_nodes) {
> struct node_stats *ns = &sp_stat.node[node];
> - struct page_state ps;
>
> /*
> * We check to see that pages are not being allocated
> @@ -375,11 +361,6 @@ static int prefetch_suitable(void)
> } else
> ns->last_free = ns->current_free;
>
> - if (!test_pagestate)
> - continue;
> -
> - get_page_state_node(&ps, node);
> -
> /* We shouldn't prefetch when we are doing writeback */
> if (node_page_state(node, NR_WRITEBACK)) {
> node_clear(node, sp_stat.prefetch_nodes);
> @@ -394,7 +375,8 @@ static int prefetch_suitable(void)
> node_page_state(node, NR_ANON) +
> node_page_state(node, NR_SLAB) +
> node_page_state(node, NR_DIRTY) +
> - ps.nr_unstable + total_swapcache_pages;
> + node_page_state(node, NR_UNSTABLE) +
> + total_swapcache_pages;
> if (limit > ns->prefetch_watermark) {
> node_clear(node, sp_stat.prefetch_nodes);
> continue;

--
-ck