On 02/24/2016 06:09 AM, Ross Zwisler wrote: > On Tue, Feb 23, 2016 at 03:56:17PM -0800, Dan Williams wrote: <> > > MAP_PMEM_AWARE is interesting, but even in a perfect world it seems like a > partial solution - applications still need to call *sync to get the FS > metadata to be durable, and they have no reliable way of knowing which of > their actions will cause the metadata to be out of sync. > So there is the very simple answer: Just like today. Today you need to call m/fsync after you have finished all modifications and you want a persistent point. This of course will work. .I.E write the application same as if the mount is not dax. But do set the flag and switch to pmem_memcpy all over. BTW pmem_memcpy() will give you 10% gain on memory performance with fully-cached FS a swell. I do not mind that. Just that with MAP_PMEM_AWARE the call to sync will be fast and the page-faults much much faster. I'm a pragmatic person I'm saying to application writers. Change nothing, have the same source code for both DAX and none DAX mode. Just switch to pmem_memcpy() / pmem_flush() everywhere and set the mmap flag, and you have 3x boost on your mmap performance. > Dave, is your objection to the MAP_SYNC idea a practical one about complexity > and time to get it implemented, or do you think it's is the wrong solution? So you see with MAP_SYNC you are asking developers to write two versions of their app, the later which does not call m/fsync. [BTW MAP_SYNC is a *very bad* name because with it you are requiring the applications to switch to pmem_memcpy() and persistent stores everywhere. It might be very confusing and people might assume that the Kernel can magically guess every time an mmap pointer was modified, even after the page-fault. It should be called something like MAP_PMEM_SYNC ] > _______________________________________________ > Linux-nvdimm mailing list > Linux-nvdimm@xxxxxxxxxxxx > https://lists.01.org/mailman/listinfo/linux-nvdimm > -- 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>