Re: removing PD_ALL_VISIBLE

On 30.05.2013 15:12, Andres Freund wrote:
> Now, I am far from being convinced its a good idea to get rid of
> PD_ALL_VISIBLE, but I don't think it does. Except that it currently is
> legal for the page level ALL_VISIBLE being set while the corresponding
> visibilitymap one isn't there's not much prohibiting us fundamentally
> from looking in the vm when we need to know whether the page is all
> visible, is there?

Hmm, so you're suggesting that the visibility map would be *required* to 
interpret the pages correctly. Ie. if you just zapped the visibility 
map, you'd lose critical information and the heap would appear to be 
corrupt. I guess that's possible, but it makes me quite uneasy. At the 
moment, it's relieving to know that it's always safe to just truncate 
the visibility map in case of emergency.

- Heikki