Re: [PATCH v2 6/6] powerpc: Don't flush caches when adding memory

[Alastair D'Silva]

On Tue, 2019-09-03 at 08:23 +0200, Christophe Leroy wrote:
> 
> Le 03/09/2019 à 07:24, Alastair D'Silva a écrit :
> > From: Alastair D'Silva 
> > 
> > This operation takes a significant amount of time when hotplugging
> > large amounts of memory (~50 seconds with 890GB of persistent
> > memory).
> > 
> > This was orignally in commit fb5924fddf9e
> > ("powerpc/mm: Flush cache on memory hot(un)plug") to support
> > memtrace,
> > but the flush on add is not needed as it is flushed on remove.
> > 
> > Signed-off-by: Alastair D'Silva 
> > ---
> >   arch/powerpc/mm/mem.c | 7 ---
> >   1 file changed, 7 deletions(-)
> > 
> > diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c
> > index 854aaea2c6ae..2a14b5b93e19 100644
> > --- a/arch/powerpc/mm/mem.c
> > +++ b/arch/powerpc/mm/mem.c
> > @@ -111,7 +111,6 @@ int __ref arch_add_memory(int nid, u64 start,
> > u64 size,
> >   {
> > unsigned long start_pfn = start >> PAGE_SHIFT;
> > unsigned long nr_pages = size >> PAGE_SHIFT;
> > -   u64 i;
> > int rc;
> >   
> > resize_hpt_for_hotplug(memblock_phys_mem_size());
> > @@ -124,12 +123,6 @@ int __ref arch_add_memory(int nid, u64 start,
> > u64 size,
> > return -EFAULT;
> > }
> >   
> > -   for (i = 0; i < size; i += FLUSH_CHUNK_SIZE) {
> > -   flush_dcache_range(start + i,
> > -  min(start + size, start + i +
> > FLUSH_CHUNK_SIZE));
> > -   cond_resched();
> > -   }
> > -
> 
> So you are removing the code you added in patch 4. Why not move this
> one 
> before patch 4 ?
> 

I put them in this order so that if someone did want the flushes in
arch_add_memory, they could drop the later patch, but not trigger RCU
stalls.

-- 
Alastair D'Silva
Open Source Developer
Linux Technology Centre, IBM Australia
mob: 0423 762 819

Re: [PATCH v2 6/6] powerpc: Don't flush caches when adding memory

[Christophe Leroy]

Le 03/09/2019 à 07:24, Alastair D'Silva a écrit :

From: Alastair D'Silva 

This operation takes a significant amount of time when hotplugging
large amounts of memory (~50 seconds with 890GB of persistent memory).

This was orignally in commit fb5924fddf9e
("powerpc/mm: Flush cache on memory hot(un)plug") to support memtrace,
but the flush on add is not needed as it is flushed on remove.

Signed-off-by: Alastair D'Silva 
---
  arch/powerpc/mm/mem.c | 7 ---
  1 file changed, 7 deletions(-)

diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c
index 854aaea2c6ae..2a14b5b93e19 100644
--- a/arch/powerpc/mm/mem.c
+++ b/arch/powerpc/mm/mem.c
@@ -111,7 +111,6 @@ int __ref arch_add_memory(int nid, u64 start, u64 size,
  {
unsigned long start_pfn = start >> PAGE_SHIFT;
unsigned long nr_pages = size >> PAGE_SHIFT;
-   u64 i;
int rc;
  
  	resize_hpt_for_hotplug(memblock_phys_mem_size());

@@ -124,12 +123,6 @@ int __ref arch_add_memory(int nid, u64 start, u64 size,
return -EFAULT;
}
  
-	for (i = 0; i < size; i += FLUSH_CHUNK_SIZE) {

-   flush_dcache_range(start + i,
-  min(start + size, start + i + 
FLUSH_CHUNK_SIZE));
-   cond_resched();
-   }
-


So you are removing the code you added in patch 4. Why not move this one 
before patch 4 ?



return __add_pages(nid, start_pfn, nr_pages, restrictions);
  }
  



Christophe

[PATCH v2 6/6] powerpc: Don't flush caches when adding memory

[Alastair D'Silva]

From: Alastair D'Silva 

This operation takes a significant amount of time when hotplugging
large amounts of memory (~50 seconds with 890GB of persistent memory).

This was orignally in commit fb5924fddf9e
("powerpc/mm: Flush cache on memory hot(un)plug") to support memtrace,
but the flush on add is not needed as it is flushed on remove.

Signed-off-by: Alastair D'Silva 
---
 arch/powerpc/mm/mem.c | 7 ---
 1 file changed, 7 deletions(-)

diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c
index 854aaea2c6ae..2a14b5b93e19 100644
--- a/arch/powerpc/mm/mem.c
+++ b/arch/powerpc/mm/mem.c
@@ -111,7 +111,6 @@ int __ref arch_add_memory(int nid, u64 start, u64 size,
 {
unsigned long start_pfn = start >> PAGE_SHIFT;
unsigned long nr_pages = size >> PAGE_SHIFT;
-   u64 i;
int rc;
 
resize_hpt_for_hotplug(memblock_phys_mem_size());
@@ -124,12 +123,6 @@ int __ref arch_add_memory(int nid, u64 start, u64 size,
return -EFAULT;
}
 
-   for (i = 0; i < size; i += FLUSH_CHUNK_SIZE) {
-   flush_dcache_range(start + i,
-  min(start + size, start + i + 
FLUSH_CHUNK_SIZE));
-   cond_resched();
-   }
-
return __add_pages(nid, start_pfn, nr_pages, restrictions);
 }
 
-- 
2.21.0