On 10/02/2013 05:51 PM, John Stultz wrote: > From: Minchan Kim <minchan@xxxxxxxxxx> > > This patch adds new system call sys_vrange. > > NAME > vrange - Mark or unmark range of memory as volatile > vrange() is about as nondescriptive as one can get -- there is exactly one letter that has any connection with that this does. > SYNOPSIS > int vrange(unsigned_long start, size_t length, int mode, > int *purged); > > DESCRIPTION > Applications can use vrange(2) to advise the kernel how it should > handle paging I/O in this VM area. The idea is to help the kernel > discard pages of vrange instead of reclaiming when memory pressure > happens. It means kernel doesn't discard any pages of vrange if > there is no memory pressure. > > mode: > VRANGE_VOLATILE > hint to kernel so VM can discard in vrange pages when > memory pressure happens. > VRANGE_NONVOLATILE > hint to kernel so VM doesn't discard vrange pages > any more. > > If user try to access purged memory without VRANGE_NOVOLATILE call, > he can encounter SIGBUS if the page was discarded by kernel. > > purged: Pointer to an integer which will return 1 if > mode == VRANGE_NONVOLATILE and any page in the affected range > was purged. If purged returns zero during a mode == > VRANGE_NONVOLATILE call, it means all of the pages in the range > are intact. I'm a bit confused about the "purged" >From an earlier version of the patch: > - What's different with madvise(DONTNEED)? > > System call semantic > > DONTNEED makes sure user always can see zero-fill pages after > he calls madvise while vrange can see data or encounter SIGBUS. This difference doesn't seem to be a huge one. The other one seems to be the blocking status of MADV_DONTNEED, which perhaps may be better handled by adding an option (MADV_LAZY) perhaps? That way we would have lazy vs. immediate, and zero versus SIGBUS. I see from the change history of the patch that this was an madvise() at some point, but was changed into a separate system call at some point, does anyone remember why that was? A quick look through my LKML archives doesn't really make it clear. -hpa -- 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>