On Thu, Jan 20, 2022 at 06:32:29PM +0800, Peter Xu wrote: > > Except that here we have no page to check, so it looks like you'll > > have to change should_zap_page() to deal with this case too, or just > > check details->check_mapping directly. > > Yeah I prefer this, as we don't have the page* pointer anyway. > > > Which raises the question again > > of why I did not just use a boolean flag there originally: aah, I think > > I've found why. In those days there was a horrible "optimization", for > > better performance on some benchmark I guess, which when you read from > > /dev/zero into a private mapping, would map the zero page there (look > > up read_zero_pagealigned() and zeromap_page_range() if you dare). So > > there was another category of page to be skipped along with the anon > > COWs, and I didn't want multiple tests in the zap loop, so checking > > check_mapping against page->mapping did both. I think nowadays you > > could do it by checking for PageAnon page (or genuine swap entry) > > instead. > > It must be PageAnon already, isn't it? I think I see what you meant now.. I assume the special case is gone, how about I switch zap_mappings back into a boolean altogether in this patchset? Thanks, -- Peter Xu
