On Thu, Apr 19, 2018 at 09:39:53PM +0100, Al Viro wrote: > On Thu, Apr 19, 2018 at 01:25:13PM -0700, Matthew Wilcox wrote: > > On Thu, Apr 19, 2018 at 04:15:02PM -0400, Jerome Glisse wrote: > > > On Thu, Apr 19, 2018 at 12:56:37PM -0700, Matthew Wilcox wrote: > > > > > Well scratch that whole idea, i would need to add a new array to task > > > > > struct which make it a lot less appealing. Hence a better solution is > > > > > to instead have this as part of mm (well indirectly). > > > > > > > > It shouldn't be too bad to add a struct radix_tree to the fdtable. > > > > > > > > I'm sure we could just not support weird cases like sharing the fdtable > > > > without sharing the mm. Does anyone actually do that? > > > > > > Well like you pointed out what i really want is a 1:1 structure linking > > > a device struct an a mm_struct. Given that this need to be cleanup when > > > mm goes away hence tying this to mmu_notifier sounds like a better idea. > > > > > > I am thinking of adding a hashtable to mmu_notifier_mm using file id for > > > hash as this should be a good hash value for common cases. I only expect > > > few drivers to need that (GPU drivers, RDMA). Today GPU drivers do have > > > a hashtable inside their driver and they has on the mm struct pointer, > > > i believe hash mmu_notifier_mm using file id will be better. > > > > file descriptors are small positive integers ... > > ... except when there's a lot of them. Or when something uses dup2() in > interesting ways, but hey - we could "just not support" that, right? > > > ideal for the radix tree. > > If you need to find your data based on the struct file address, then by > > all means a hashtable is the better data structure. > > Perhaps it would be a good idea to describe whatever is being attempted? > > FWIW, passing around descriptors is almost always a bloody bad idea. There > are very few things really associated with those and just about every time > I'd seen internal APIs that work in terms of those "small positive numbers" > they had been badly racy and required massive redesign to get something even > remotely sane. Ok i will use struct device pointer as index, or something else (i would like to use PCI domain:bus:slot but i don't want this to be PCIE only), maybe dev_t ... Cheers, Jérôme
