linux-ext4 - Re: [PATCH] ext4: slab caches set to SLAB_MEM

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Message-Id: <8343168C-D5F7-43E4-B614-45FBAF5B29A7@mit.edu>
Date:	Thu, 17 Nov 2011 10:11:07 -0500
From:	Theodore Tso <tytso@....EDU>
To:	NamJae Jeon <linkinjeon@...il.com>
Cc:	Theodore Tso <tytso@....edu>, David Rientjes <rientjes@...gle.com>,
	linux-kernel@...r.kernel.org, linux-ext4@...r.kernel.org,
	Amit Sahrawat <amit.sahrawat83@...il.com>
Subject: Re: [PATCH] ext4: slab caches set to SLAB_MEM_SPREAD flags.

On Nov 17, 2011, at 12:35 AM, NamJae Jeon wrote:

> We prevent one node being concentrating workload from redundant
> alloc/free by balancing workload to other nodes in performance side.
> and we can avoid reclaim probability a little by allocation from only
> local node also.

Can you say more about this?   I'm afraid I don't understand what you
are trying to do here.

What I'm worried about is systems where the memory latency time for
local versus remote nodes might be 2-3 to 1.  That is, it takes 2-3 times
as much time to access memory on a remote node.   (On older machines,
the memory access time ratio's could have been as bad as 12:1 or 15:1.)

So accessing non-local memory can be a really, really big deal.  And this
isn't just theoretical, but have you considered what might happen on a 8
core AMD machine?

Regards,

-- Ted

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