[resend] Revert "powerpc/powernv: Increase memory block size to 1GB on radix"

[resend] Revert "powerpc/powernv: Increase memory block size to 1GB on radix"

[Balbir Singh]

This commit was a stop-gap to prevent crashes on hotunplug, caused by
the mismatch between the 1G mappings used for the linear mapping and the
memory block size. Those issues are now resolved because we split the
linear mapping at hotunplug time if necessary, as implemented in commit
4dd5f8a99e79 ("powerpc/mm/radix: Split linear mapping on hot-unplug").

Signed-off-by: Balbir Singh <bsingharora@gmail.com>
Signed-off-by: Michael Neuling <mikey@neuling.org>
---

Resend with a newer commit message grabbed from an email sent by mpe.

 arch/powerpc/platforms/powernv/setup.c | 10 +---------
 1 file changed, 1 insertion(+), 9 deletions(-)

diff --git a/arch/powerpc/platforms/powernv/setup.c b/arch/powerpc/platforms/powernv/setup.c
index ef8c9ce53a61..fa63d3fff14c 100644
--- a/arch/powerpc/platforms/powernv/setup.c
+++ b/arch/powerpc/platforms/powernv/setup.c
@@ -356,15 +356,7 @@ static void pnv_kexec_cpu_down(int crash_shutdown, int secondary)
 #ifdef CONFIG_MEMORY_HOTPLUG_SPARSE
 static unsigned long pnv_memory_block_size(void)
 {
-	/*
-	 * We map the kernel linear region with 1GB large pages on radix. For
-	 * memory hot unplug to work our memory block size must be at least
-	 * this size.
-	 */
-	if (radix_enabled())
-		return 1UL * 1024 * 1024 * 1024;
-	else
-		return 256UL * 1024 * 1024;
+	return 256UL * 1024 * 1024;
 }
 #endif
 
-- 
2.13.6

Re: [resend] Revert "powerpc/powernv: Increase memory block size to 1GB on radix"

[rashmica]

Tested hot-unplugging dimm device on radix guest on p9 host with KVM.


On 01/05/18 12:57, Balbir Singh wrote:
> This commit was a stop-gap to prevent crashes on hotunplug, caused by
> the mismatch between the 1G mappings used for the linear mapping and the
> memory block size. Those issues are now resolved because we split the
> linear mapping at hotunplug time if necessary, as implemented in commit
> 4dd5f8a99e79 ("powerpc/mm/radix: Split linear mapping on hot-unplug").
>
> Signed-off-by: Balbir Singh <bsingharora@gmail.com>
> Signed-off-by: Michael Neuling <mikey@neuling.org>
Tested-by: Rashmica Gupta <rashmica.g@gmail.com>
> ---
>
> Resend with a newer commit message grabbed from an email sent by mpe.
>
>  arch/powerpc/platforms/powernv/setup.c | 10 +---------
>  1 file changed, 1 insertion(+), 9 deletions(-)
>
> diff --git a/arch/powerpc/platforms/powernv/setup.c b/arch/powerpc/platforms/powernv/setup.c
> index ef8c9ce53a61..fa63d3fff14c 100644
> --- a/arch/powerpc/platforms/powernv/setup.c
> +++ b/arch/powerpc/platforms/powernv/setup.c
> @@ -356,15 +356,7 @@ static void pnv_kexec_cpu_down(int crash_shutdown, int secondary)
>  #ifdef CONFIG_MEMORY_HOTPLUG_SPARSE
>  static unsigned long pnv_memory_block_size(void)
>  {
> -	/*
> -	 * We map the kernel linear region with 1GB large pages on radix. For
> -	 * memory hot unplug to work our memory block size must be at least
> -	 * this size.
> -	 */
> -	if (radix_enabled())
> -		return 1UL * 1024 * 1024 * 1024;
> -	else
> -		return 256UL * 1024 * 1024;
> +	return 256UL * 1024 * 1024;
>  }
>  #endif
>  

Re: [resend] Revert "powerpc/powernv: Increase memory block size to 1GB on radix"

[Balbir Singh]

On Wed, 2 May 2018 15:10:33 +1000
rashmica <rashmica.g@gmail.com> wrote:

> Tested hot-unplugging dimm device on radix guest on p9 host with KVM.
> 
> 
> On 01/05/18 12:57, Balbir Singh wrote:
> > This commit was a stop-gap to prevent crashes on hotunplug, caused by
> > the mismatch between the 1G mappings used for the linear mapping and the
> > memory block size. Those issues are now resolved because we split the
> > linear mapping at hotunplug time if necessary, as implemented in commit
> > 4dd5f8a99e79 ("powerpc/mm/radix: Split linear mapping on hot-unplug").
> >
> > Signed-off-by: Balbir Singh <bsingharora@gmail.com>
> > Signed-off-by: Michael Neuling <mikey@neuling.org>  
> Tested-by: Rashmica Gupta <rashmica.g@gmail.com>

I tested the following:

a. memtrace  - enable a region smaller than 1G, which split the mappings
as expected.
b. Checked linear mapping is 1G and not impacted by the revert
c. I can hotplug sizes less than 1G via the probe method

Tested-by: Balbir Singh <bsingharora@gmail.com>

> > ---
> >
> > Resend with a newer commit message grabbed from an email sent by mpe.
> >
> >  arch/powerpc/platforms/powernv/setup.c | 10 +---------
> >  1 file changed, 1 insertion(+), 9 deletions(-)
> >
> > diff --git a/arch/powerpc/platforms/powernv/setup.c b/arch/powerpc/platforms/powernv/setup.c
> > index ef8c9ce53a61..fa63d3fff14c 100644
> > --- a/arch/powerpc/platforms/powernv/setup.c
> > +++ b/arch/powerpc/platforms/powernv/setup.c
> > @@ -356,15 +356,7 @@ static void pnv_kexec_cpu_down(int crash_shutdown, int secondary)
> >  #ifdef CONFIG_MEMORY_HOTPLUG_SPARSE
> >  static unsigned long pnv_memory_block_size(void)
> >  {
> > -	/*
> > -	 * We map the kernel linear region with 1GB large pages on radix. For
> > -	 * memory hot unplug to work our memory block size must be at least
> > -	 * this size.
> > -	 */
> > -	if (radix_enabled())
> > -		return 1UL * 1024 * 1024 * 1024;
> > -	else
> > -		return 256UL * 1024 * 1024;
> > +	return 256UL * 1024 * 1024;
> >  }
> >  #endif
> >    
> 

Re: [resend] Revert "powerpc/powernv: Increase memory block size to 1GB on radix"

[Michael Ellerman]

On Tue, 2018-05-01 at 02:57:25 UTC, Balbir Singh wrote:
> This commit was a stop-gap to prevent crashes on hotunplug, caused by
> the mismatch between the 1G mappings used for the linear mapping and the
> memory block size. Those issues are now resolved because we split the
> linear mapping at hotunplug time if necessary, as implemented in commit
> 4dd5f8a99e79 ("powerpc/mm/radix: Split linear mapping on hot-unplug").
> 
> Signed-off-by: Balbir Singh <bsingharora@gmail.com>
> Signed-off-by: Michael Neuling <mikey@neuling.org>
> Tested-by: Rashmica Gupta <rashmica.g@gmail.com>
> Tested-by: Balbir Singh <bsingharora@gmail.com>

Applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/7acf50e4efa60270edcb95107f660f

cheers