Re: Memory pressure handling with iSCSI

[Badari Pulavarty <pbadari@us.ibm.com>]

On Tue, 2005-07-26 at 17:31 -0700, Andrew Morton wrote:
> Badari Pulavarty <pbadari@us.ibm.com> wrote:
> >
> > On Tue, 2005-07-26 at 16:07 -0700, Andrew Morton wrote:
> >  > Badari Pulavarty <pbadari@us.ibm.com> wrote:
> >  > >
> >  > > Here is the data with 5 ext2 filesystems. I also collected /proc/meminfo
> >  > > every 5 seconds. As you can see, we seem to dirty 6GB of data in 20
> >  > > seconds of starting the test. I am not sure if its bad, since we have
> >  > > lots of free memory..
> >  > 
> >  > It's bad.  The logic in balance_dirty_pages() should block those write()
> >  > callers as soon as we hit 40% dirty memory or whatever is in
> >  > /proc/sys/vm/dirty_ratio.  So something is horridly busted.
> >  > 
> >  > Can you try reducing the number of filesystems even further?
> > 
> >  Single ext2 filesystem. We still dirty pretty quickly (data collected
> >  every 5 seconds).
> 
> It happens here, a bit.  My machine goes up to 60% dirty when it should be
> clamping at 40%.
> 
> The variable `total_pages' in page-writeback.c (from
> nr_free_pagecache_pages()) is too high.  I trace it back to here:
> 
> On node 0 totalpages: 1572864
>   DMA zone: 4096 pages, LIFO batch:1
>   Normal zone: 1568768 pages, LIFO batch:31
>   HighMem zone: 0 pages, LIFO batch:1
> 
> This machine only has 4G of memory, so the platform code is overestimating
> the number of pages by 50%.  Can you please check your dmesg, see if your
> system is also getting this wrong?



On node 0 totalpages: 1572863
  DMA zone: 4096 pages, LIFO batch:1
  Normal zone: 1568767 pages, LIFO batch:31
  HighMem zone: 0 pages, LIFO batch:1
On node 1 totalpages: 131071
  DMA zone: 0 pages, LIFO batch:1
  Normal zone: 131071 pages, LIFO batch:31
  HighMem zone: 0 pages, LIFO batch:1
On node 2 totalpages: 131071
  DMA zone: 0 pages, LIFO batch:1
  Normal zone: 131071 pages, LIFO batch:31
  HighMem zone: 0 pages, LIFO batch:1
On node 3 totalpages: 131071
  DMA zone: 0 pages, LIFO batch:1
  Normal zone: 131071 pages, LIFO batch:31
  HighMem zone: 0 pages, LIFO batch:1



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