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    SubjectRe: [PATCH 19/21] swap_prefetch: Conversion of nr_unstable to ZVC
    Date
    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
    -
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