Re: shrink_mmap() change in ac-21

[Rik van Riel <riel@conectiva.com.br>]

On 19 Jun 2000, Zlatko Calusic wrote:

> The shrink_mmap() change in your latest prepatch (ac12) doesn't look
> very healthy. Removing the test for the wrong zone we effectively
> discard lots of wrong pages before we get to the right one. That is
> effectively flushing the page cache and we have unbalanced system.
> 
> For example, check the "vmstat 1" output below, done while I was
> reading a big file from the disk. At some point in time, the page
> cache shrunk to almost half of its size (75MB -> 42MB).
> 
> The reason is balancing of the DMA zone (which is much smaller on a
> 128MB machine than the NORMAL zone!). shrink_mmap() now happily evicts
> wrong pages from the memory and continues doing so until it finally
> frees enough pages from the DMA zone. That, of course, hurts caching
> as the page cache gets shrunk a lot without a good reason.

I already suspected this could happen.

/me looks at quintela

Juan, didn't you and Roger have a patch to solve this? ;)
(I think quintela and roger already have a patch so I'll save
writing one myself)

regards,

Rik
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