2009-10-01 14:03:23

by Suresh Jayaraman

Subject: [PATCH 01/31] mm: serialize access to min_free_kbytes

From: Peter Zijlstra <[email protected]>

There is a small race between the procfs caller and the memory hotplug caller
of setup_per_zone_wmarks(). Not a big deal, but the next patch will add yet
another caller. Time to close the gap.

Signed-off-by: Peter Zijlstra <[email protected]>
Signed-off-by: Suresh Jayaraman <[email protected]>
---
mm/page_alloc.c | 16 +++++++++++++---
1 file changed, 13 insertions(+), 3 deletions(-)

Index: mmotm/mm/page_alloc.c
===================================================================
--- mmotm.orig/mm/page_alloc.c
+++ mmotm/mm/page_alloc.c
@@ -121,6 +121,7 @@ static char * const zone_names[MAX_NR_ZO
"Movable",
};

+static DEFINE_SPINLOCK(min_free_lock);
int min_free_kbytes = 1024;

unsigned long __meminitdata nr_kernel_pages;
@@ -4448,13 +4449,13 @@ static void setup_per_zone_lowmem_reserv
}

/**
- * setup_per_zone_wmarks - called when min_free_kbytes changes
+ * __setup_per_zone_wmarks - called when min_free_kbytes changes
* or when memory is hot-{added|removed}
*
* Ensures that the watermark[min,low,high] values for each zone are set
* correctly with respect to min_free_kbytes.
*/
-void setup_per_zone_wmarks(void)
+static void __setup_per_zone_wmarks(void)
{
unsigned long pages_min = min_free_kbytes >> (PAGE_SHIFT - 10);
unsigned long lowmem_pages = 0;
@@ -4552,6 +4553,15 @@ static void __init setup_per_zone_inacti
calculate_zone_inactive_ratio(zone);
}

+void setup_per_zone_wmarks(void)
+{
+ unsigned long flags;
+
+ spin_lock_irqsave(&min_free_lock, flags);
+ __setup_per_zone_wmarks();
+ spin_unlock_irqrestore(&min_free_lock, flags);
+}
+
/*
* Initialise min_free_kbytes.
*
@@ -4587,7 +4597,7 @@ static int __init init_per_zone_wmark_mi
min_free_kbytes = 128;
if (min_free_kbytes > 65536)
min_free_kbytes = 65536;
- setup_per_zone_wmarks();
+ __setup_per_zone_wmarks();
setup_per_zone_lowmem_reserve();
setup_per_zone_inactive_ratio();
return 0;

2009-10-01 20:35:54

by David Rientjes

Subject: Re: [PATCH 01/31] mm: serialize access to min_free_kbytes

On Thu, 1 Oct 2009, Suresh Jayaraman wrote:

> From: Peter Zijlstra <[email protected]>
>
> There is a small race between the procfs caller and the memory hotplug caller
> of setup_per_zone_wmarks(). Not a big deal, but the next patch will add yet
> another caller. Time to close the gap.
>

By "next patch," you mean "mm: emegency pool" (patch 08/31)?

If so, can't you eliminate var_free_mutex entirely from that patch and
take min_free_lock in adjust_memalloc_reserve() instead?

[ __adjust_memalloc_reserve() would call __setup_per_zone_wmarks()
under lock instead, now. ]

2009-10-02 05:19:22

by NeilBrown

Subject: Re: [PATCH 01/31] mm: serialize access to min_free_kbytes

On Thursday October 1, [email protected] wrote:
> On Thu, 1 Oct 2009, Suresh Jayaraman wrote:
>
> > From: Peter Zijlstra <[email protected]>
> >
> > There is a small race between the procfs caller and the memory hotplug caller
> > of setup_per_zone_wmarks(). Not a big deal, but the next patch will add yet
> > another caller. Time to close the gap.
> >
>
> By "next patch," you mean "mm: emegency pool" (patch 08/31)?

:-) It is always safer to say "a subsequent patch", isn't it....

>
> If so, can't you eliminate var_free_mutex entirely from that patch and
> take min_free_lock in adjust_memalloc_reserve() instead?

adjust_memalloc_reserve does a test alloc/free cycle under a lock.
That cannot be done under a spin-lock, it must be a mutex.
So I don't think you can eliminate var_free_mutex.

Thanks,
NeilBrown

>
> [ __adjust_memalloc_reserve() would call __setup_per_zone_wmarks()
> under lock instead, now. ]