[-next] rename of VM_NR_PDFLUSH_THREADS breaks strace compilation

[Heiko Carstens]

On Fri, Dec 07, 2018 at 05:53:13AM -0500, Rafael Aquini wrote:
> On Fri, Dec 07, 2018 at 08:58:07AM +0100, Heiko Carstens wrote:
> > Hi Rafael,
> > 
> > your patch 77cab92a2cb1 ("sysctl: clean up nr_pdflush_threads
> > leftover") in linux-next breaks strace compilation if used with kernel
> > headers from linux-next.
> > -       VM_NR_PDFLUSH_THREADS=15, /* nr_pdflush_threads */
> > +       VM_UNUSED15=15,         /* was: int: nr_pdflush_threads */
> The nr_pdflush_threads (VM_NR_PDFLUSH_THREADS) tunable has been obsolete since 2.6.32
> and it was, excepting by the bit in the referred patch, completely removed on 4.15.
> 
> I think you just need to patch strace source with the following hunk, in
> order to reflect the removal. Would you mind checking it?
> 
> diff --git a/xlat/sysctl_vm.in b/xlat/sysctl_vm.in
> index 3c2b4739..30784c2a 100644
> --- a/xlat/sysctl_vm.in
> +++ b/xlat/sysctl_vm.in
> @@ -5,7 +5,6 @@ VM_DIRTY_BACKGROUND
>  VM_DIRTY_RATIO
>  VM_DIRTY_WB_CS
>  VM_DIRTY_EXPIRE_CS
> -VM_NR_PDFLUSH_THREADS
>  VM_OVERCOMMIT_RATIO
>  VM_PAGEBUF
>  VM_HUGETLB_PAGES

I'll leave that up to Dmitry to decide what to do here. At least it
won't be possible to compile old strace versions with new kernel
headers if the kernel change gets merged upstream.