Re: [PATCH]: Free pages from local pcp lists under tight memory conditions

Andrew Morton
2005-11-23T05:58:38Z

Andrew Morton <akpm@osdl.org> wrote:
>
> The `while' loop worries me for some reason, so I wimped out and just tried
> the remote drain once.

Even the `goto restart' which is in this patch worries me from a livelock
POV. Perhaps we should only ever run drain_all_local_pages() once per
__alloc_pages() invokation.

And perhaps we should run drain_all_local_pages() for GFP_ATOMIC or
PF_MEMALLOC attempts too.

--- devel/include/linux/gfp.h~mm-free-pages-from-local-pcp-lists-under-tight-memory-conditions 2005-11-22 21:47:33.000000000 -0800
+++ devel-akpm/include/linux/gfp.h 2005-11-22 21:57:22.000000000 -0800
@@ -109,6 +109,8 @@ static inline struct page *alloc_pages_n
NODE_DATA(nid)->node_zonelists + gfp_zone(gfp_mask));
}

+extern void drain_local_pages(void);
+
#ifdef CONFIG_NUMA
extern struct page *alloc_pages_current(gfp_t gfp_mask, unsigned order);

diff -puN include/linux/suspend.h~mm-free-pages-from-local-pcp-lists-under-tight-memory-conditions include/linux/suspend.h
--- devel/include/linux/suspend.h~mm-free-pages-from-local-pcp-lists-under-tight-memory-conditions 2005-11-22 21:47:33.000000000 -0800
+++ devel-akpm/include/linux/suspend.h 2005-11-22 21:47:33.000000000 -0800
@@ -40,7 +40,6 @@ extern dev_t swsusp_resume_device;
extern int shrink_mem(void);

/* mm/page_alloc.c */
-extern void drain_local_pages(void);
extern void mark_free_pages(struct zone *zone);

#ifdef CONFIG_PM
diff -puN mm/page_alloc.c~mm-free-pages-from-local-pcp-lists-under-tight-memory-conditions mm/page_alloc.c
--- devel/mm/page_alloc.c~mm-free-pages-from-local-pcp-lists-under-tight-memory-conditions 2005-11-22 21:47:33.000000000 -0800
+++ devel-akpm/mm/page_alloc.c 2005-11-22 21:58:01.000000000 -0800
@@ -578,32 +578,65 @@ void drain_remote_pages(void)
}
#endif

-#if defined(CONFIG_PM) || defined(CONFIG_HOTPLUG_CPU)
-static void __drain_pages(unsigned int cpu)
+/*
+ * Drain any cpu-local pages into the buddy lists. Must be called under
+ * local_irq_disable().
+ */
+static int __drain_pages(unsigned int cpu)
{
- unsigned long flags;
struct zone *zone;
- int i;
+ int ret = 0;

for_each_zone(zone) {
struct per_cpu_pageset *pset;
+ int i;

pset = zone_pcp(zone, cpu);
for (i = 0; i < ARRAY_SIZE(pset->pcp); i++) {
struct per_cpu_pages *pcp;

pcp = &pset->pcp[i];
- local_irq_save(flags);
+ if (!pcp->count)
+ continue;
pcp->count -= free_pages_bulk(zone, pcp->count,
&pcp->list, 0);
- local_irq_restore(flags);
+ ret++;
}
}
+ return ret;
}
-#endif /* CONFIG_PM || CONFIG_HOTPLUG_CPU */

-#ifdef CONFIG_PM
+/*
+ * Spill all of this CPU's per-cpu pages back into the buddy allocator.
+ */
+void drain_local_pages(void)
+{
+ unsigned long flags;
+
+ local_irq_save(flags);
+ __drain_pages(smp_processor_id());
+ local_irq_restore(flags);
+}

+static void drainer(void *p)
+{
+ drain_local_pages();
+}
+
+/*
+ * Drain the per-cpu pages on all CPUs. If called from interrupt context we
+ * can only drain the local CPU's pages, since cross-CPU calls are deadlocky
+ * from interrupt context.
+ */
+static void drain_all_local_pages(void)
+{
+ if (in_interrupt())
+ drain_local_pages();
+ else
+ on_each_cpu(drainer, NULL, 0, 1);
+}
+
+#ifdef CONFIG_PM
void mark_free_pages(struct zone *zone)
{
unsigned long zone_pfn, flags;
@@ -629,17 +662,6 @@ void mark_free_pages(struct zone *zone)
spin_unlock_irqrestore(&zone->lock, flags);
}

-/*
- * Spill all of this CPU's per-cpu pages back into the buddy allocator.
- */
-void drain_local_pages(void)
-{
- unsigned long flags;
-
- local_irq_save(flags);
- __drain_pages(smp_processor_id());
- local_irq_restore(flags);
-}
#endif /* CONFIG_PM */

static void zone_statistics(struct zonelist *zonelist, struct zone *z)
@@ -889,6 +911,10 @@ restart:
if (gfp_mask & __GFP_HIGH)
alloc_flags |= ALLOC_DIP_LESS;

+ if (order > 0 || (!wait && (gfp_mask & __GFP_HIGH)) ||
+ (p->flags & PF_MEMALLOC))
+ drain_all_local_pages();
+
page = get_page_from_freelist(gfp_mask, order, zonelist, alloc_flags);
if (page)
goto got_pg;
_