On Wed, May 22, 2024 at 05:20:08PM +0800, Lance Yang wrote: > On Wed, May 22, 2024 at 4:38 PM Brendan Jackman <jackmanb@xxxxxxxxxx> wrote: > > > > Hi Lance, thanks for taking a look. > > > > On Wed, May 22, 2024 at 12:25:30PM +0800, Lance Yang wrote: > > > Hi Brendan, > > > > > > On Tue, May 21, 2024 at 8:57 PM Brendan Jackman <jackmanb@xxxxxxxxxx> wrote: > > > > @@ -1077,7 +1081,7 @@ void adjust_present_page_count(struct page *page, struct memory_group *group, > > > > */ > > > > if (early_section(__pfn_to_section(page_to_pfn(page)))) > > > > zone->present_early_pages += nr_pages; > > > > - zone->present_pages += nr_pages; > > > > + WRITE_ONCE(zone->present_pages, zone->present_pages + nr_pages); > > > > > > I'm not sure that using the WRITE_ONCE() wrapper would prevent load tearing > > > on 'zone->present_pages', but it's probably just me overthinking it :) > > > > Hmm.. this isn't for load-tearing, it's for store-tearing. I have a > > feeling I might be missing your pont here though, can you elaborate? > > Sorry, my explanation wasn't clear :( > > I'm a bit confused about whether 'WRITE_ONCE(zone->present_pages, > zone->present_pages + nr_pages);' > is equivalent to the following: > > 1 a = zone->present_pages + nr_pages; > 2 WRITE_ONCE(zone->present_pages, a); > > If so, is there any possibility of load tearing on > 'zone->present_pages' in line 1? Ah gotcha, thanks for clarifying. Loads are protected by mem_hotplug_lock here, so it's fine for them to get split up (because the value can't change between loads). This is what I was referring to in the bit of the commit message about not needing READ_ONCE.
