Peter Zijlstra wrote:
On Mon, 17 Sep 2007 15:04:05 +0100 Anton Altaparmakov <[email protected]>
wrote:
They files
are attached this time rather than inlined so people don't complain
about line wrapping! (No doubt people will not complain about them
being attached! )-:)
I switched mailer after I learnt about flowed stuffs. Still,
appreciated.
If I read it correctly it appears all of low memory is eaten up by
buffer_heads.
<quote>
# name <active_objs> <num_objs> <objsize> <objperslab>
<pagesperslab>
: tunables <limit> <batchcount> <sharedfactor> : slabdata
<active_slabs> <num_s
labs> <sharedavail>
buffer_head 12569528 12569535 56 67 1 : tunables
120 60 8 :
slabdata 187605 187605 0
</quote>
That is 671MiB of low memory in buffer_heads.
But why is the kernel not reclaiming them by getting rid of the page
cache pages they are attached to or even leaving the pages around but
killing their buffers?
Well, you see, you have this very odd configuration where:
11GB highmem
1GB normal
pagecache pages go into highmem
buggerheads go into normal
I'm guessing there is no pressure at all on zone_highmem so the
kernel will not try to reclaim pagecache. And because the pagecache
pages are happily sitting there, the buggerheads are pinned and do not
get reclaimed.
I've got code for this in RHEL 3, but never bothered to
merge it upstream since I thought people with large memory
systems would be running 64 bit kernels by now.
Obviously I was wrong. Andrew, are you interested in a
fix for this problem?
IIRC I simply kept a list of all buffer heads and walked
that to reclaim pages when the number of buffer heads is
too high (and we need memory). This list can be maintained
in places where we already hold the lock for the buffer head
freelist, so there should be no additional locking overhead
(again, IIRC).
--
Politics is the struggle between those who want to make their country
the best in the world, and those who believe it already is. Each group
calls the other unpatriotic.
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