On Wed, Nov 22, 2017 at 07:30:50PM +0000, Will Deacon wrote: > Hi Michal, > > On Mon, Nov 20, 2017 at 05:04:22PM +0100, Michal Hocko wrote: > > On Mon 20-11-17 14:24:44, Will Deacon wrote: > > > On Thu, Nov 16, 2017 at 10:20:42AM +0100, Michal Hocko wrote: > > > > On Wed 15-11-17 17:33:32, Will Deacon wrote: > > [...] > > > > > > diff --git a/arch/arm64/include/asm/tlb.h b/arch/arm64/include/asm/tlb.h > > > > > > index ffdaea7954bb..7adde19b2bcc 100644 > > > > > > --- a/arch/arm64/include/asm/tlb.h > > > > > > +++ b/arch/arm64/include/asm/tlb.h > > > > > > @@ -43,7 +43,7 @@ static inline void tlb_flush(struct mmu_gather *tlb) > > > > > > * The ASID allocator will either invalidate the ASID or mark > > > > > > * it as used. > > > > > > */ > > > > > > - if (tlb->fullmm) > > > > > > + if (tlb->lazy) > > > > > > return; > > > > > > > > > > This looks like the right idea, but I'd rather make this check: > > > > > > > > > > if (tlb->fullmm && tlb->lazy) > > > > > > > > > > since the optimisation doesn't work for anything than tearing down the > > > > > entire address space. > > > > > > > > OK, that makes sense. > > > > > > > > > Alternatively, I could actually go check MMF_UNSTABLE in tlb->mm, which > > > > > would save you having to add an extra flag in the first place, e.g.: > > > > > > > > > > if (tlb->fullmm && !test_bit(MMF_UNSTABLE, &tlb->mm->flags)) > > > > > > > > > > which is a nice one-liner. > > > > > > > > But that would make it oom_reaper specific. What about the softdirty > > > > case Minchan has mentioned earlier? > > > > > > We don't (yet) support that on arm64, so we're ok for now. If we do grow > > > support for it, then I agree that we want a flag to identify the case where > > > the address space is going away and only elide the invalidation then. > > > > What do you think about the following patch instead? I have to confess > > I do not really understand the fullmm semantic so I might introduce some > > duplication by this flag. If you think this is a good idea, I will post > > it in a separate thread. > > > Please do! My only suggestion would be s/lazy/exit/, since I don't think the > optimisation works in any other situation than the address space going away > for good. Yes, address space going. That's why I wanted to add additional check that address space going without adding new flags. http://lkml.kernel.org/r/<20171113002833.GA18301@bbox> However, if you guys love to add new flag to distinguish, I prefer "exit" to "lazy". It also would be better to add WARN_ON to catch future potential wrong use case like OOM reaper. Anyway, I'm not strong against so it up to you, Michal. WARN_ON_ONCE(exit == true && atomic_read(&mm->mm_users) > 0); -- 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>
