mmap
mmap
Posted Apr 21, 2013 0:07 UTC (Sun) by plougher (guest, #21620)In reply to: mmap by mjw
Parent article: LFCS: Preparing Linux for nonvolatile memory devices
> Does anybody have a reference with some more background on why mmap() might not be salvageable?
Well an obvious observation is mmap is page oriented and NVM is byte orientated/accessible. If you're layering a filesystem on top of NVM you don't have to align the files to block boundaries or pad, but can pack much more closely... But without block alignment you loose the ability to mmap the file (you can copy to intermediate aligned buffers but this is extra overhead).
CRAMFS-XIP (compressed filesystem with execute in place extensions on NOR flash) has exactly this problem. NOR is memory addressable and thus directly mmapable. However, if you want to execute in place, you can't compress or pack the file in CRAMFS.