On 08/13/2015 03:57 PM, Dan Williams wrote: <> > This is explicitly addressed in the changelog, repeated here: > >> The __pfn_t to resource lookup is indeed inefficient walking of a linked list, >> but there are two mitigating factors: >> >> 1/ The number of persistent memory ranges is bounded by the number of >> DIMMs which is on the order of 10s of DIMMs, not hundreds. >> You do not get where I'm comming from. It used to be a [ptr - ONE_BASE + OTHER_BASE] (In 64 bit) it is now a call and a loop and a search. how ever you will look at it is *not* the instantaneous address translation it is now. I have memory I want memory speeds. You keep thinking HD speeds, where what ever you do will not matter. >> 2/ The lookup yields the entire range, if it becomes inefficient to do a >> kmap_atomic_pfn_t() a PAGE_SIZE at a time the caller can take >> advantage of the fact that the lookup can be amortized for all kmap >> operations it needs to perform in a given range. > What "given range" how can a bdev assume that the all sg-list belongs to the same "range". In fact our code does multple-pmem devices for a long time. What about say md-of-pmems for example, or btrfs > DAX as is is races against pmem unbind. A synchronization cost must > be paid somewhere to make sure the memremap() mapping is still valid. Sorry for being so slow, is what I asked. what is exactly "pmem unbind" ? Currently in my 4.1 Kernel the ioremap is done on modprobe time and released modprobe --remove time. the --remove can not happen with a mounted FS dax or not. So what is exactly "pmem unbind". And if there is a new knob then make it refuse with a raised refcount. Cheers Boaz -- 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>