Messages in this thread | | | From | "JaniD++" <> | Subject | Re: buffer cache question | Date | Thu, 29 Dec 2005 17:26:28 +0100 |
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Hi,
----- Original Message ----- From: "Nate Diller" <nate.diller@gmail.com> To: "JaniD++" <djani22@dynamicweb.hu> Cc: <linux-kernel@vger.kernel.org>; <pavel@suse.cz> Sent: Thursday, December 29, 2005 5:10 AM Subject: Re: buffer cache question
> > ----- Original Message ----- > > From: Nate Diller > > To: JaniD++ > > Cc: Roger Heflin ; linux-kernel@vger.kernel.org > > Sent: Friday, December 23, 2005 9:58 AM > > Subject: Re: buffer cache question > > > > looks like you're barely using any of your high memory. maybe NBD doesn't > > have highmem support. what file system are you using? > > > > NATE > > > > > > I cannot understant this. > > NBD need to support highmem for buffering? > > If know right, the kernel does buffering, not NBD! > > But the kernel only use ~830MB for buffer cache instead of dinamically use > > all free memory like page cache. > > > > This is one raw disk node, independent from file system. > > > > this is an NBD client, using CONFIG_BLK_DEV_NBD? on the 2.6 series > kernel? if so, then it, like any other kernel component using the > page cache, needs to explicity use kmap/kunmap to make use of memory > in the high memory zone. on a 32 bit machine, any pages above the 896 > meg mark are treated specially inside the linux kernel (see > http://kerneltrap.org/node/2450).
Yes, i have read this helpful document, but there is about the memory usage, mapping, and not exactly the buffering/caching. Yes, i use the 2.6 series NBD.
> > if you don't have highmem support (CONFIG_HIGHMEM4G) enabled, then > enabling that should fix it. if you already have it enabled (it > looked like it to me, based on your /proc/meminfo) then there is a bug > somewhere.
Yes, it is enabled.
> > it would seem from a brief inspection that the send/recv_bvec > functions in nbd (2.6.13) do use kmap. I don't know the nbd code very > well, it seems that Pavel Machek wrote the code, he or block layer > maintainer Jens Axboe may know something I don't. So if enabling > highmem in your .config doesn't help, try CC'ing them with your issue. > in the mean time, one of the memory split patches, such as the 4G:4G > patch, should get things working.
The NBD use buffer cache (i am sure), but the highest limit is about 830-840M.
Where can i get the split patch?
Thanks for helpful answers!
Cheers, Janos
> > NATE
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