On Thu, 2019-08-15 at 09:36 +0200, christophe leroy wrote:
>
> Le 15/08/2019 à 06:10, Alastair D'Silva a écrit :
> > From: Alastair D'Silva <alast...@d-silva.org>
> >
> > When presented with large amounts of memory being hotplugged
> > (in my test case, ~890GB), the call to flush_dcache_range takes
> > a while (~50 seconds), triggering RCU stalls.
> >
> > This patch breaks up the call into 16GB chunks, calling
> > cond_resched() inbetween to allow the scheduler to run.
>
> Is 16GB small enough ? If 890GB takes 50s, 16GB still takes about 1s.
> I'd use 1GB chuncks to remain below 100ms.
>
> > Signed-off-by: Alastair D'Silva <alast...@d-silva.org>
> > ---
> > arch/powerpc/mm/mem.c | 16 ++++++++++++++--
> > 1 file changed, 14 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c
> > index 5400da87a804..fb0d5e9aa11b 100644
> > --- a/arch/powerpc/mm/mem.c
> > +++ b/arch/powerpc/mm/mem.c
> > @@ -104,11 +104,14 @@ int __weak remove_section_mapping(unsigned
> > long start, unsigned long end)
> > return -ENODEV;
> > }
> >
> > +#define FLUSH_CHUNK_SIZE (16ull * 1024ull * 1024ull * 1024ull)
>
> Can we use SZ_16GB ?
Sure, I'll go with 1GB as you recommended above
> > +
> > int __ref arch_add_memory(int nid, u64 start, u64 size,
> > struct mhp_restrictions *restrictions)
> > {
> > unsigned long start_pfn = start >> PAGE_SHIFT;
> > unsigned long nr_pages = size >> PAGE_SHIFT;
> > + unsigned long i;
> > int rc;
> >
> > resize_hpt_for_hotplug(memblock_phys_mem_size());
> > @@ -120,7 +123,11 @@ int __ref arch_add_memory(int nid, u64 start,
> > u64 size,
> > start, start + size, rc);
> > return -EFAULT;
> > }
> > - flush_dcache_range(start, start + size);
> > +
> > + for (i = 0; i < size; i += FLUSH_CHUNK_SIZE) {
> > + flush_dcache_range(start + i, min(start + size, start +
> > i + FLUSH_CHUNK_SIZE));
>
> Isn't the line a bit long (I have not checked).
>
> > + cond_resched();
> > + }
> >
> > return __add_pages(nid, start_pfn, nr_pages, restrictions);
> > }
> > @@ -131,13 +138,18 @@ void __ref arch_remove_memory(int nid, u64
> > start, u64 size,
> > unsigned long start_pfn = start >> PAGE_SHIFT;
> > unsigned long nr_pages = size >> PAGE_SHIFT;
> > struct page *page = pfn_to_page(start_pfn) +
> > vmem_altmap_offset(altmap);
> > + unsigned long i;
> > int ret;
> >
> > __remove_pages(page_zone(page), start_pfn, nr_pages, altmap);
> >
> > /* Remove htab bolted mappings for this section of memory */
> > start = (unsigned long)__va(start);
> > - flush_dcache_range(start, start + size);
> > + for (i = 0; i < size; i += FLUSH_CHUNK_SIZE) {
> > + flush_dcache_range(start + i, min(start + size, start +
> > i + FLUSH_CHUNK_SIZE));
> > + cond_resched();
> > + }
> > +
> > ret = remove_section_mapping(start, start + size);
> > WARN_ON_ONCE(ret);
> >
> >
>
> Christophe
>
> ---
> L'absence de virus dans ce courrier électronique a été vérifiée par
> le logiciel antivirus Avast.
> https://urldefense.proofpoint.com/v2/url?u=https-3A__www.avast.com_antivirus&d=DwIDaQ&c=jf_iaSHvJObTbx-siA1ZOg&r=cT4tgeEQ0Ll3SIlZDHE5AEXyKy6uKADMtf9_Eb7-vec&m=TBT2NNM2DXqDWHhSb_WdFPcfAjYk9hP2cvGksF001cQ&s=XURKAOQQ4h3_RhJlezSguD2kpSitAF-uBhQqVZLU4GU&e=
>
>
--
Alastair D'Silva
Open Source Developer
Linux Technology Centre, IBM Australia
mob: 0423 762 819
