On 03/09/2015 12:51, Michal Hocko wrote:
On Thu 03-09-15 12:07:03, Navin Parakkal wrote: [...]
The problem doesn't occur with Oracle systems because during backup they have ways to use direct I/O and many DBAs set that by default . ... When you are backing up TeraBytes of data ie full export and backup , i think it is better not to fill up the kernel caches that you are going to seldom use.
I am still not sure I understand what is _the problem_. Do you see any considerable stalls during backups caused by excessive slab usage? You have mentioned that you can see stalls during an artificial load earlier but nothing about a real world example.
As end user, I can suggest an scenario. I don't know if it relates to SLAB/SLUB, but I know that it is a real scenario similar to the one Navin describes. On some systems, when writing the openSUSE DVD iso image to an USB stick, as the stick is slow writing, the kernel tries to cache as much as it can in memory, maybe the full 4 gigs. This, apparently, has the consequence of starving other processes of cache use and ram, on some machines, causing the entire machine to crawl and become unresponsive for minutes. Using certain flags with dd to drop the cache helps, but it would be better to tell the kernel to limit the amount of cache used for a certain device, or per process, or have it automatically use the proper decisions, whatever they be :-) -- Saludos/Cheers, Carlos E.R. (Minas-Morgul - W7) -- To unsubscribe, e-mail: opensuse-kernel+unsubscribe@opensuse.org To contact the owner, e-mail: opensuse-kernel+owner@opensuse.org