On Tue, 23 Oct 2012 10:00:18 +0300 "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx> wrote: > > Well, how hard is it to trigger the bad behavior? One can easily > > create a situation in which that page's refcount frequently switches > > from 0 to 1 and back again. And one can easily create a situation in > > which the shrinkers are being called frequently. Run both at the same > > time and what happens? > > If the goal is to trigger bad behavior then: > > 1. read from an area where a huge page can be mapped to get huge zero page > mapped. hzp is allocated here. refcounter == 2. > 2. write to the same page. refcounter == 1. > 3. echo 3 > /proc/sys/vm/drop_caches. refcounter == 0 -> free the hzp. > 4. goto 1. > > But it's unrealistic. /proc/sys/vm/drop_caches is only root-accessible. Yes, drop_caches is uninteresting. > We can trigger shrinker only under memory pressure. But in this, most > likely we will get -ENOMEM on hzp allocation and will go to fallback path > (4k zero page). I disagree. If, for example, there is a large amount of clean pagecache being generated then the shrinkers will be called frequently and memory reclaim will be running at a 100% success rate. The hugepage allocation will be successful in such a situation? -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>