Re: Subtle MM bug

[Marcelo Tosatti <marcelo@conectiva.com.br>]

On Tue, 9 Jan 2001, Linus Torvalds wrote:

> 
> On Tue, 9 Jan 2001, Marcelo Tosatti wrote:
> > 
> > > > The second problem is that background scanning is being done
> > > > unconditionally, and it should not. You end up getting all pages with the
> > > > same age if the system is idle. Look at this example (2.4.1-pre1):
> > > 
> > > I agree. However, I think that we do want to do some background scanning
> > > to push out dirty pages in the background, kind of like bdflush. It just
> > > shouldn't age the pages (and thus not move them to the inactive list).
> > 
> > Actually it must age the pages, but aging should not be unconditional. 
> 
> No, I'm saying that "the background scanning" should not do the page
> aging.

If you age pages only when there is memory pressure/low memory, you'll
have less knowledge about which pages were unused/used pages over time.

> Obviously "refill_inactive()" needs to do the page aging. I'm just not at
> all convinced that "background scanning" == "refill_inactive()". 

This is the background scanning I refer (in kswapd):

                /*
                 * Do some (very minimal) background scanning. This
                 * will scan all pages on the active list once
                 * every minute. This clears old referenced bits
                 * and moves unused pages to the inactive list.
                 */
                refill_inactive_scan(6, 0);




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