On 30 September 2014 04:51, Hugh Dickins <hughd@xxxxxxxxxx> wrote: > On Fri, 26 Sep 2014, Steve Capper wrote: > >> get_user_pages_fast attempts to pin user pages by walking the page >> tables directly and avoids taking locks. Thus the walker needs to be >> protected from page table pages being freed from under it, and needs >> to block any THP splits. >> >> One way to achieve this is to have the walker disable interrupts, and >> rely on IPIs from the TLB flushing code blocking before the page table >> pages are freed. >> >> On some platforms we have hardware broadcast of TLB invalidations, thus >> the TLB flushing code doesn't necessarily need to broadcast IPIs; and >> spuriously broadcasting IPIs can hurt system performance if done too >> often. >> >> This problem has been solved on PowerPC and Sparc by batching up page >> table pages belonging to more than one mm_user, then scheduling an >> rcu_sched callback to free the pages. This RCU page table free logic >> has been promoted to core code and is activated when one enables >> HAVE_RCU_TABLE_FREE. Unfortunately, these architectures implement >> their own get_user_pages_fast routines. >> >> The RCU page table free logic coupled with a an IPI broadcast on THP >> split (which is a rare event), allows one to protect a page table >> walker by merely disabling the interrupts during the walk. >> >> This patch provides a general RCU implementation of get_user_pages_fast >> that can be used by architectures that perform hardware broadcast of >> TLB invalidations. >> >> It is based heavily on the PowerPC implementation by Nick Piggin. >> >> Signed-off-by: Steve Capper <steve.capper@xxxxxxxxxx> >> Tested-by: Dann Frazier <dann.frazier@xxxxxxxxxxxxx> >> Reviewed-by: Catalin Marinas <catalin.marinas@xxxxxxx> > > Acked-by: Hugh Dickins <hughd@xxxxxxxxxx> > Thanks Hugh! > Thanks for making all those clarifications, Steve: this looks very > good to me now. I'm not sure which tree you're hoping will take this > and the arm+arm64 patches 2-6: although this one would normally go > through akpm, I expect it's easier for you to synchronize if it goes > in along with the arm+arm64 2-6 - would that be okay with you, Andrew? > I see no clash with what's currently in mmotm. I see it's gone into mmotm. -- 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>