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SubjectRe: [PATCH v2 6/6] powerpc: Don't flush caches when adding memory
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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 <alastair@d-silva.org>
> >
> > 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 <alastair@d-silva.org>
> > ---
> > 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

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