On Wed 04-06-14 12:19:33, Jeff Mahoney wrote:
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On 6/4/14, 12:07 PM, Jean Delvare wrote:
Hi Cristian,
Le Tuesday 27 May 2014 à 11:49 -0400, Cristian Rodríguez a écrit :
Just out of curiosity, why SUSE kernels default to CONFIG_SLAB and not CONFIG_SLUB ? I just checked the rest of current distribution world and everyone else takes the kernel default.
I am assuming there is a reason for this, that it is intentional and not a oversight where somebody forgot changing the configuration...
The topic was already brought up for discussion in July 2008: http://lists.opensuse.org/opensuse-kernel/2008-07/msg00014.html
While SLUB was already the default for one year, Jeff did not think it was the right time to switch. The lack of explanation in the upstream commit that changed the default may explain it :-(
Almost 6 years later, I guess we can revisit this. While I am not familiar with SLAB vs. SLUB, I see that: * There must be a reason why SLUB is the default, and there is nothing extraordinary about openSUSE that I can think of that would justify not sticking to that default. * Using what the majority is using should make it less likely to hit a bug. And if there is a bug, it is likely to be fixed much faster.
I really do not remember any bug in SLAB during last years. The code is pretty much stable.
So unless someone can provide a good reason why we should stick to SLAB, I vote for switching to SLUB.
I vote against unless there's a compelling reason to change it.
Agreed.
Sometimes the default changes upstream because it's new and shiny and more or less working. It's a way to improve test coverage. The problem is that test coverage in most cases just means that it doesn't crash.
I asked Mel about this on IRC a few days ago and the response was along the lines of "it's the devil we know." He also mentioned that he recalled the last time he looked into it there were still network performance regressions that hadn't been fixed yet.
That may have changed since the last time he looked at it, but without confirmation, I'm going to assume they're still there. So far I haven't seen a compelling reason to change it other than "it's the default." I'd suggest that anyone pushing to change the choice in allocator be willing to actually do that testing and post the numbers and breadth of the test coverage before we do change it.
Slub allows debugging which can be turned on during runtime which is much better than in slab which has to compile debugging in which is quite impractical. But this doesn't sound like a real reason to switch our default I guess. -- Michal Hocko SUSE Labs -- To unsubscribe, e-mail: opensuse-kernel+unsubscribe@opensuse.org To contact the owner, e-mail: opensuse-kernel+owner@opensuse.org