On Mon, Jul 24, 2017 at 05:27:47PM -0700, Nadav Amit wrote: > > Do we still need the barrier()s or is it OK to let the atomic op do > > that for us (with a suitable code comment). > > I will submit v2. However, I really don???t understand the comment on > mm_tlb_flush_pending(): > > /* > * Memory barriers to keep this state in sync are graciously provided by > * the page table locks, outside of which no page table modifications happen. > * The barriers below prevent the compiler from re-ordering the instructions > * around the memory barriers that are already present in the code. > */ > > But IIUC migrate_misplaced_transhuge_page() does not call > mm_tlb_flush_pending() while the ptl is taken. > > Mel, can I bother you again? Should I move the flush in > migrate_misplaced_transhuge_page() till after the ptl is taken? > The flush, if it's necessary, needs to happen before the copy. However, in this particular context it shouldn't matter. In this specific context, we must be dealing with a NUMA hinting fault which means the original PTE is PROT_NONE, flushed and no writes are possible. If a protection update happens during the copy in migrate_misplaced_transhuge_page then it'll be detected in migrate_misplaced_transhuge_page by the pmd_same check and the page copy was a waste of time but otherwise harmless. -- Mel Gorman SUSE Labs -- 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>
