On 01/12/2016 13:50, Balbir Singh wrote: > 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. That's a good question ;) I may be too optimistic / naive, and I'm not confident in the result of such a goal but I think it may be good to keep such a direction in mind. It may be possible to limit its usage as it has been done in the fs part. Laurent. -- 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>