Re: [DATAPOINT] pre7-6 will not swap

[Rajagopal Ananthanarayanan <ananth@sgi.com>]

Linus Torvalds wrote:
> 
	[ ... ]
> 
> The "don't page out pages from zones that don't need it" test is a good
> test, but it turns out that it triggers a rather serious problem: the way
> the buffer cache dirty page handling is done is by having shrink_mmap() do
> a "try_to_free_buffers()" on the pages it encounters that have
> "page->buffer" set.
> 
> And doing that is quite important, because without that logic the buffers
> don't get written to disk in a timely manner, nor do already-written
> buffers get refiled to their proper lists. So you end up being "out of
> memory" - not because the machine is really out of memory, but because
> those buffers have a tendency to stick around if they aren't constantly
> looked after by "try_to_free_buffers()".
> 
> So the real fix ended up being to re-order the tests in shrink_mmap() a
> bit, so that try_to_free_buffers() is called even for pages that are on
> a good zone that doesn't need any real balancing..

Not sure entirely what effect this has, except for freeing underlying
buffer_head's. The page itself is still skipped. Anyway, brief examination
shows that you've changed several things here (in 7-7), so I'll have to go
at it some more time to get a full picture.

> 
> [ time passes ]
> 
> pre7-7 is there now.
> 
>                 Linus

Unfortunately my dbench test really runs bad with pre 7-7.
Quantitively, the amount of memory in "cache" of vmstat
is higher than before. write()'s start failing. 

More later,

-- 
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Rajagopal Ananthanarayanan ("ananth")
Member Technical Staff, SGI.
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