On Mon, 27 Jul 2015, Kirill A. Shutemov wrote: > On Mon, Jul 27, 2015 at 09:41:26AM -0400, Eric B Munson wrote: > > On Mon, 27 Jul 2015, Kirill A. Shutemov wrote: > > > > > On Fri, Jul 24, 2015 at 05:28:43PM -0400, Eric B Munson wrote: > > > > The cost of faulting in all memory to be locked can be very high when > > > > working with large mappings. If only portions of the mapping will be > > > > used this can incur a high penalty for locking. > > > > > > > > Now that we have the new VMA flag for the locked but not present state, > > > > expose it as an mmap option like MAP_LOCKED -> VM_LOCKED. > > > > > > As I mentioned before, I don't think this interface is justified. > > > > > > MAP_LOCKED has known issues[1]. The MAP_LOCKED problem is not necessary > > > affects MAP_LOCKONFAULT, but still. > > > > > > Let's not add new interface unless it's demonstrably useful. > > > > > > [1] http://lkml.kernel.org/g/20150114095019.GC4706@xxxxxxxxxxxxxx > > > > I understand and should have been more explicit. This patch is still > > included becuase I have an internal user that wants to see it added. > > The problem discussed in the thread you point out does not affect > > MAP_LOCKONFAULT because we do not attempt to populate the region with > > MAP_LOCKONFAULT. > > > > As I told Vlastimil, if this is a hard NAK with the patch I can work > > with that. Otherwise I prefer it stays. > > That's not how it works. I am not sure what you mean here. I have a user that will find this useful and MAP_LOCKONFAULT does not suffer from the problem you point out. I do not understand your NAK but thank you for explicit about it. > > Once an ABI added to the kernel it stays there practically forever. > Therefore it must be useful to justify maintenance cost. I don't see it > demonstrated. I understand this, and I get that you do not like MAP_LOCKED, but I do not see how your dislike for MAP_LOCKED means that this would not be useful. > > So, NAK. > V6 will not have the new mmap flag unless there is someone else that speaks up in favor of keeping it.
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