Re: [PATCH v7 2/4] mm/memory.c: Update local TLB if PTE entry exists

[Andrew Morton]

On Wed, 27 May 2020 10:25:18 +0800 Bibo Mao <maobibo@xxxxxxxxxxx> wrote:

> If two threads concurrently fault at the same page, the thread that
> won the race updates the PTE and its local TLB. For now, the other
> thread gives up, simply does nothing, and continues.
> 
> It could happen that this second thread triggers another fault, whereby
> it only updates its local TLB while handling the fault. Instead of
> triggering another fault, let's directly update the local TLB of the
> second thread. Function update_mmu_tlb is used here to update local
> TLB on the second thread, and it is defined as empty on other arches.
> 
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -2752,6 +2752,7 @@ static vm_fault_t wp_page_copy(struct vm_fault *vmf)
>  		new_page = old_page;
>  		page_copied = 1;
>  	} else {
> +		update_mmu_tlb(vma, vmf->address, vmf->pte);
>  		mem_cgroup_cancel_charge(new_page, memcg, false);
>  	}
>  

When applying your patches on top of the -mm tree's changes, the above
hunk didn't apply.  The entire `else' block was removed by
https://ozlabs.org/~akpm/mmotm/broken-out/mm-memcontrol-convert-anon-and-file-thp-to-new-mem_cgroup_charge-api.patch

I assumed that dropping this hunk was appropriate.  Please check?