Re: Memory pressure handling with iSCSI

[Andrew Morton <akpm@osdl.org>]

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?
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