[PATCH] ext4: group info caches set to SLAB_MEM_SPREAD flags.

[PATCH] ext4: group info caches set to SLAB_MEM_SPREAD flags.

[Namjae Jeon]

If group info caches set to SLAB_MEM_SPREAD flags, the allocation is spread evenly over all the memory nodes when using cpuset.
It is useful because group info caches are long lived.

Signed-off-by: Namjae Jeon <linkinjeon@gmail.com>
Signed-off-by: Amit Sahrawat <amit.sahrawat83@gmail.com>
---
 fs/ext4/mballoc.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index e2d8be8..7aacbbe 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -2407,7 +2407,8 @@ static int ext4_groupinfo_create_slab(size_t size)
 				bb_counters[blocksize_bits + 2]);
 
 	cachep = kmem_cache_create(ext4_groupinfo_slab_names[cache_index],
-					slab_size, 0, SLAB_RECLAIM_ACCOUNT,
+					slab_size, 0, SLAB_RECLAIM_ACCOUNT |
+					SLAB_MEM_SPREAD,
 					NULL);
 
 	ext4_groupinfo_caches[cache_index] = cachep;
-- 
1.7.4.4

Re: [PATCH] ext4: group info caches set to SLAB_MEM_SPREAD flags.

[David Rientjes]

On Sun, 20 Nov 2011, Namjae Jeon wrote:

> If group info caches set to SLAB_MEM_SPREAD flags, the allocation is 
> spread evenly over all the memory nodes when using cpuset.

Incorrect, it also requires the cpuset to enable cpuset.memory_spread_slab 
which is not the default.

> It is useful because group info caches are long lived.
> 

As mentioned earlier, you should be able to get performance data as a 
result of this change by using any kernel, enabling CONFIG_CPUSETS and 
CONFIG_SLAB, mounting cpusets at runtime, enabling 
cpuset.memory_spread_slab, creating a mempolicy of MPOL_INTERLEAVE over 
all nodes, and then running your comparison benchmark.  This requires no 
modification of the kernel and will determine what performance benefit 
there is by doing this on your own hardware that you're interested in.

If there is convincing data that suggests it's helpful on your hardware, 
then it would make a good case to merge your patch so users don't need to 
set their own mempolicies that do this.  They'll just need to mount 
cpusets and enable cpuset.memory_spread_slab.

Absent that, there's no purpose in adding this flag.  If you're doing it 
just because it's done in other filesystems, mention that in the changelog 
so it can be judged on that criteria rather than pretending like the NUMA 
affinity actually means anything to your environment.

Re: [PATCH] ext4: group info caches set to SLAB_MEM_SPREAD flags.

[Ted Ts'o]

On Sat, Nov 19, 2011 at 03:29:34PM -0800, David Rientjes wrote:
> If there is convincing data that suggests it's helpful on your hardware, 
> then it would make a good case to merge your patch so users don't need to 
> set their own mempolicies that do this.  They'll just need to mount 
> cpusets and enable cpuset.memory_spread_slab.

>From Namjae and Amit have stated, they don't have access to any NUMA
hardware.  If I had to guess they are students or people who are
trying to start a Linux development team at some company or research
institute, and have decided to start by sending cleanup patches.

	       	    	       	     	- Ted