Re: write drop behind effect on active scanning

[Rik van Riel]

On Wed, 23 May 2001, Marcelo Tosatti wrote:

> I just noticed a "bad" effect of write drop behind yesterday during some
> tests.
>
> The problem is that we deactivate written pages, thus making the inactive
> list become pretty big (full of unfreeable pages) under write intensive IO
> workloads.
>
> So what happens is that we don't do _any_ aging on the active list, and in
> the meantime the inactive list (which should have "easily" freeable
> pages) is full of locked pages.
>
> I'm going to fix this one by replacing "deactivate_page(page)" to
> "ClearPageReferenced(page)" in generic_file_write(). This way the written
> pages are aged faster but we avoid the bad effect just described.
>
> Any comments on the fix ?

1) I agree with it, drop-behind should make the pages we write
   very likely for eviction, but we don't want that to stop the
   eviction of other not-used pages ...

2) OTOH, if writeout of dirty pages is a problem for the system,
   I guess we will want to fix that problem somehow ;)
   (but that's another issue)

regards,

Rik
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