On Fri, May 15, 2015 at 02:56:42PM +0200, Vlastimil Babka wrote: > On 04/23/2015 11:03 PM, Kirill A. Shutemov wrote: > >With new refcounting THP can belong to several VMAs. This makes tricky > >to track THP pages, when they partially mlocked. It can lead to leaking > >mlocked pages to non-VM_LOCKED vmas and other problems. > > > >With this patch we will split all pages on mlock and avoid > >fault-in/collapse new THP in VM_LOCKED vmas. > > > >I've tried alternative approach: do not mark THP pages mlocked and keep > >them on normal LRUs. This way vmscan could try to split huge pages on > >memory pressure and free up subpages which doesn't belong to VM_LOCKED > >vmas. But this is user-visible change: we screw up Mlocked accouting > >reported in meminfo, so I had to leave this approach aside. > > > >We can bring something better later, but this should be good enough for > >now. > > I can imagine people won't be happy about losing benefits of THP's when they > mlock(). > How difficult would it be to support mlocked THP pages without splitting > until something actually tries to do a partial (un)mapping, and only then do > the split? That will support the most common case, no? Yes, it will. But what will we do if we fail to split huge page on munmap()? Fail munmap() with -EBUSY? -- Kirill A. Shutemov -- 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>