----- Original Message -----
From: Nate Diller
To: JaniD++
Cc: Roger Heflin ; [email protected]
Sent: Friday, December 23, 2005 9:58 AM
Subject: Re: buffer cache question
On 11/21/05, JaniD++ <[email protected]> wrote:
Hi,
I have read back in the kernel-archives, and found this messages, about the
same theme, but there is one difference!
On the old messages:
>Nate Diller wrote:
> just found the culprit. guess i should have read the code the first
> time. get_dirty_limits() in drivers/block/page_writeback.c has a
> hard-coded upper limit to dirty_ratio. it's capped to half of the
> unmapped pages, so maybe 30-40% of your system's memory. so if you are
> brave, just remove the "/ 2" parts from the 'if (dirty_ratio >
> unmapped_ratio / 2) dirty_ratio = unmapped_ratio / 2;' check, and you
> can have all the OOM goodness you want.
...
>I changed that bit of code to:
>
> if (dirty_ratio > unmapped_ratio - 10)
> dirty_ratio = unmapped_ratio - 10;
>
>and added a couple of sanity checks so that it couldn't get below 5 or
above 95.
>
>Then set /proc/sys/vm/dirty_ratio to 95 and dirty_background_ratio to 1.
In this case, this modification is only for the *dirty* memory buffer.
I want to use more buffer *cache*! :-)
The unwritten dirty memory ratio is good enough for me.
Anybody has an idea?
<snip>
> > [root@st-0001 root]# free
> > total used free shared
> > buffers cached
> > Mem: 2073152 933188 1139964 0
> > 836776 43416
> > -/+ buffers/cache: 52996 2020156
> > Swap: 0 0 0
> > [root@st-0001 root]# cat /proc/meminfo
> > MemTotal: 2073152 kB
> > MemFree: 1139012 kB
> > Buffers: 835928 kB
> > Cached: 43448 kB
> > SwapCached: 0 kB
> > Active: 12872 kB
> > Inactive: 871424 kB
> > HighTotal: 1179584 kB
> > HighFree: 1129764 kB
> > LowTotal: 893568 kB
> > LowFree: 9248 kB
> > SwapTotal: 0 kB
> > SwapFree: 0 kB
> > Dirty: 0 kB
> > Writeback: 0 kB
> > Mapped: 9104 kB
> > Slab: 30248 kB
> > CommitLimit: 1036576 kB
> > Committed_AS: 15428 kB
> > PageTables: 408 kB
> > VmallocTotal: 114680 kB
> > VmallocUsed: 196 kB
> > VmallocChunk: 114476 kB
> > [root@st-0001 root]#
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.
Cheers,
Janos
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