On Tue, Apr 01, 2014 at 09:12:44PM -0700, John Stultz wrote: > On 04/01/2014 04:01 PM, Dave Hansen wrote: > > On 04/01/2014 02:35 PM, H. Peter Anvin wrote: > >> On 04/01/2014 02:21 PM, Johannes Weiner wrote: > >>> Either way, optimistic volatile pointers are nowhere near as > >>> transparent to the application as the above description suggests, > >>> which makes this usecase not very interesting, IMO. > >> ... however, I think you're still derating the value way too much. The > >> case of user space doing elastic memory management is more and more > >> common, and for a lot of those applications it is perfectly reasonable > >> to either not do system calls or to have to devolatilize first. > > The SIGBUS is only in cases where the memory is set as volatile and > > _then_ accessed, right? > Not just set volatile and then accessed, but when a volatile page has > been purged and then accessed without being made non-volatile. > > > > John, this was something that the Mozilla guys asked for, right? Any > > idea why this isn't ever a problem for them? > So one of their use cases for it is for library text. Basically they > want to decompress a compressed library file into memory. Then they plan > to mark the uncompressed pages volatile, and then be able to call into > it. Ideally for them, the kernel would only purge cold pages, leaving > the hot pages in memory. When they traverse a purged page, they handle > the SIGBUS and patch the page up. How big are these libraries compared to overall system size? > Now.. this is not what I'd consider a normal use case, but was hoping to > illustrate some of the more interesting uses and demonstrate the > interfaces flexibility. I'm just dying to hear a "normal" use case then. :) > Also it provided a clear example of benefits to doing LRU based > cold-page purging rather then full object purging. Though I think the > same could be demonstrated in a simpler case of a large cache of objects > that the applications wants to mark volatile in one pass, unmarking > sub-objects as it needs. Agreed. -- 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>