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Subject[PATCH]: Free pages from local pcp lists under tight memory conditions
Andrew, Linus,

[PATCH]: This patch free pages (pcp->batch from each list at a time) from
local pcp lists when a higher order allocation request is not able to
get serviced from global free_list.

This should help fix some of the earlier failures seen with order 1 allocations.

I will send separate patches for:

1- Reducing the remote cpus pcp
2- Clean up page_alloc.c for CONFIG_HOTPLUG_CPU to use this code appropiately

Signed-off-by: Rohit Seth <rohit.seth@intel.com>


--- a/mm/page_alloc.c 2005-11-22 07:03:40.000000000 -0800
+++ linux-2.6.15-rc2/mm/page_alloc.c 2005-11-22 07:17:48.000000000 -0800
@@ -827,6 +827,35 @@
return page;
}

+static int
+reduce_cpu_pcp(void )
+{
+ struct zone *zone;
+ unsigned long flags;
+ unsigned int cpu = get_cpu();
+ int i, ret=0;
+
+ local_irq_save(flags);
+ for_each_zone(zone) {
+ struct per_cpu_pageset *pset;
+
+ pset = zone_pcp(zone, cpu);
+ for (i = 0; i < ARRAY_SIZE(pset->pcp); i++) {
+ struct per_cpu_pages *pcp;
+
+ pcp = &pset->pcp[i];
+ if (pcp->count == 0)
+ continue;
+ pcp->count -= free_pages_bulk(zone, pcp->batch,
+ &pcp->list, 0);
+ ret++;
+ }
+ }
+ local_irq_restore(flags);
+ put_cpu();
+ return ret;
+}
+
/*
* This is the 'heart' of the zoned buddy allocator.
*/
@@ -887,6 +916,7 @@
* Ignore cpuset if GFP_ATOMIC (!wait) rather than fail alloc.
* See also cpuset_zone_allowed() comment in kernel/cpuset.c.
*/
+try_again:
page = get_page_from_freelist(gfp_mask, order, zonelist, alloc_flags);
if (page)
goto got_pg;
@@ -911,8 +941,15 @@
}

/* Atomic allocations - we can't balance anything */
- if (!wait)
- goto nopage;
+ if (!wait) {
+ /* Check if there are pages available on pcp lists that can be
+ * moved to global page list to satisfy higher order allocations.
+ */
+ if ((order > 0) && (reduce_cpu_pcp()))
+ goto try_again;
+ else
+ goto nopage;
+ }

rebalance:
cond_resched();
@@ -950,6 +987,14 @@
goto restart;
}

+ if (order > 0)
+ while (reduce_cpu_pcp()) {
+ if (get_page_from_freelist(gfp_mask, order, zonelist, alloc_flags))
+ goto got_pg;
+ }
+ /* FIXME: Add the support for reducing/draining the remote pcps.
+ */
+
/*
* Don't let big-order allocations loop unless the caller explicitly
* requests that. Wait for some write requests to complete then retry.
-
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