On Mon, Feb 18, 2019 at 09:51:33AM -0800, Zi Yan wrote: > On 18 Feb 2019, at 9:42, Vlastimil Babka wrote: > > On 2/18/19 6:31 PM, Zi Yan wrote: > > > The purpose of proposing exchange_pages() is to avoid allocating any > > > new > > > page, > > > so that we would not trigger any potential page reclaim or memory > > > compaction. > > > Allocating a temporary page defeats the purpose. > > > > Compaction can only happen for order > 0 temporary pages. Even if you > > used > > single order = 0 page to gradually exchange e.g. a THP, it should be > > better than > > u64. Allocating order = 0 should be a non-issue. If it's an issue, then > > the > > system is in a bad state and physically contiguous layout is a secondary > > concern. > > You are right if we only need to allocate one order-0 page. But this also > means > we can only exchange two pages at a time. We need to add a lock to make sure > the temporary page is used exclusively or we need to keep allocating > temporary pages > when multiple exchange_pages() are happening at the same time.
You allocate one temporary page per thread that's doing an exchange_page().
