On Thu, Dec 1, 2016 at 7:34 PM, Laurent Dufour <ldufour@xxxxxxxxxxxxxxxxxx> wrote: > On 18/11/2016 15:08, Andi Kleen wrote: >> Laurent Dufour <ldufour@xxxxxxxxxxxxxxxxxx> writes: >> >>> This is a port on kernel 4.8 of the work done by Peter Zijlstra to >>> handle page fault without holding the mm semaphore. >> >> One of the big problems with patches like this today is that it is >> unclear what mmap_sem actually protects. It's a big lock covering lots >> of code. Parts in the core VM, but also do VM callbacks in file systems >> and drivers rely on it too? >> >> IMHO the first step is a comprehensive audit and then writing clear >> documentation on what it is supposed to protect. Then based on that such >> changes can be properly evaluated. > > Hi Andi, > > Sorry for the late answer... > > I do agree, this semaphore is massively used and it would be nice to > have all its usage documented. > > I'm currently tracking all the mmap_sem use in 4.8 kernel (about 380 > hits) and I'm trying to identify which it is protecting. > > In addition, I think it may be nice to limit its usage to code under mm/ > so that in the future it may be easier to find its usage. Is this possible? All sorts of arch's fault handling/virtualization/file system and drivers (IO/DRM/) hold mmap_sem. Balbir Singh. -- 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>