On Sun, Apr 12, 2015 at 03:56:33PM +0300, Yigal Korman wrote: > Hi, > I've tried to mlock() a range of an ext4-dax file and got "-ENOMEM" in return. Is it comes from mlock_fixup() or -EFAULT from GUP translated to -ENOMEM by __mlock_posix_error_return()? > Looking at the code, it seems that this is related to the fact that > DAX uses VM_MIXEDMAP and mlock assumes/requires regular page cache. > To me it seems that DAX should simply return success in mlock() as all > data is always in memory and no swapping is possible. > Is this a bug or intentional? Is there a fix planned? I think it's a bug. But first we need to define what mlock() means for DAX mappings. For writable MAP_PRIVATE: we should be able to trigger COW for the range and mlock resulting pages. It means we should fix kernel to handle GUP(FOLL_TOUCH | FOLL_POPULATE | FOLL_WRITE | FOLL_FORCE) successfully on such VMAs. For MAP_SHARED and non-writable MAP_PRIVATE we should be able to populate the mapping with PTEs. Not sure if we need to set VM_LOCKED for such VMAs. We probably should, as we want to re-instantiate PTEs on mremap() and such. It means we need to get working at least GUP(FOLL_POPULATE | FOLL_FORCE). In general we need to adjust GUP to avoid going to struct page unless FOLL_* speficly imply struct page, such as FOLL_GET or FOLL_TOUCH. Not sure if we need to differentiate DAX mappings from other VM_MIXEDMAP. Any comments? > Also, the same code path that is used in mlock is also used for > MAP_POPULATE (pre-fault pages in mmap) so this flag doesn't work as > well (doesn't fail but simply doesn't pre-fault anything). > > Thanks, > Yigal > -- > To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- Kirill A. Shutemov -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
