On Mon, May 23, 2016 at 02:49:09PM -0400, Rik van Riel wrote: > On Mon, 2016-05-23 at 20:42 +0200, Michal Hocko wrote: > > On Mon 23-05-16 20:14:11, Ebru Akagunduz wrote: > > > > > > Currently khugepaged makes swapin readahead under > > > down_write. This patch supplies to make swapin > > > readahead under down_read instead of down_write. > > You are still keeping down_write. Can we do without it altogether? > > Blocking mmap_sem of a remote proces for write is certainly not nice. > > Maybe Andrea can explain why khugepaged requires > a down_write of mmap_sem? > > If it were possible to have just down_read that > would make the code a lot simpler.
You need a down_write() to retract page table. We need to make sure that nobody sees the page table before we can replace it with huge pmd. -- Kirill A. Shutemov
