On Fri, Oct 2, 2015 at 3:42 PM, Logan Gunthorpe <logang@xxxxxxxxxxxx> wrote: > > > On 02/10/15 03:53 PM, Dan Williams wrote: >> >> Yes, this location for dev_pagemap will not work. I've since moved it >> to a union with the lru list_head since ZONE_DEVICE pages memory >> should always have an elevated page count and never land on a slab >> allocator lru. > > > Oh, also, I was actually hoping to make use of the lru list_head in the > future with ZONE_DEVICE memory. One thought I had was once we have a PCIe > device with a BAR space, we'd then need to have a way of allocating these > buffers when user space needs them. The simple way I was thinking was to > just use the lru list head to store lists of used and unused pages -- though > there are probably other solutions to this that don't require using struct > pages. > The current assumption is the ZONE_DEVICE ranges are being managed by a physical address allocator. In the case of persistent memory this is the block allocator of the filesystem sitting on top of a pmem block device. The struct page is really only there to facilitate in-flight I/O requests. If it weren't for complexity we'd allocate them on demand. So you're "unused" case should be a raw pfn and then for the time-limited duration it is in use as a struct page it should hold a reference against the mapping. -- 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>