Re: [patch 5/18] mark swapout pages PageWriteback()

[Linus Torvalds]

On Fri, 31 May 2002, Andrea Arcangeli wrote:
> 
> In short the same way MAP_ANON must pageout correctly, also MAP_SHARED
> must swapout correctly with very vm intensive conditions.

That is true, but it is ignoring the fact that there _are_ real technical 
differences between swap cache mappings and regular shared mappings.

One major difference is the approach to the last user: a last use of a 
shared mapping still needs to write out dirty state, while the last use of 
a swap page is better off noticing that it should just optimize away the 
write, and we can just turn the page back into a dirty anonymous page.

But the differences are much smaller than many of the similarities.

		Linus