Comment below...
On Thu, 26 Sep 2019 at 12:18, Alastair D'Silva <alast...@au1.ibm.com> wrote: > > 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 1GB chunks, calling > cond_resched() inbetween to allow the scheduler to run. > > Signed-off-by: Alastair D'Silva <alast...@d-silva.org> > --- > arch/powerpc/mm/mem.c | 27 +++++++++++++++++++++++++-- > 1 file changed, 25 insertions(+), 2 deletions(-) > > diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c > index cff947cb2a84..a2758e473d58 100644 > --- a/arch/powerpc/mm/mem.c > +++ b/arch/powerpc/mm/mem.c > @@ -104,6 +104,27 @@ int __weak remove_section_mapping(unsigned long start, > unsigned long end) > return -ENODEV; > } > > +#define FLUSH_CHUNK_SIZE SZ_1G > +/** > + * flush_dcache_range_chunked(): Write any modified data cache blocks out to > + * memory and invalidate them, in chunks of up to FLUSH_CHUNK_SIZE > + * Does not invalidate the corresponding instruction cache blocks. > + * > + * @start: the start address > + * @stop: the stop address (exclusive) > + * @chunk: the max size of the chunks > + */ > +static void flush_dcache_range_chunked(unsigned long start, unsigned long > stop, > + unsigned long chunk) > +{ > + unsigned long i; > + > + for (i = start; i < stop; i += FLUSH_CHUNK_SIZE) { Here you ignore the function parameter "chunk" and use the define FLUSH_CHUNK_SIZE. You should do one or the other; use the parameter or remove it. > + flush_dcache_range(i, min(stop, start + FLUSH_CHUNK_SIZE)); > + cond_resched(); > + } > +} > + > int __ref arch_add_memory(int nid, u64 start, u64 size, > struct mhp_restrictions *restrictions) > { > @@ -120,7 +141,8 @@ int __ref arch_add_memory(int nid, u64 start, u64 size, > start, start + size, rc); > return -EFAULT; > } > - flush_dcache_range(start, start + size); > + > + flush_dcache_range_chunked(start, start + size, FLUSH_CHUNK_SIZE); > > return __add_pages(nid, start_pfn, nr_pages, restrictions); > } > @@ -137,7 +159,8 @@ void __ref arch_remove_memory(int nid, u64 start, u64 > size, > > /* Remove htab bolted mappings for this section of memory */ > start = (unsigned long)__va(start); > - flush_dcache_range(start, start + size); > + flush_dcache_range_chunked(start, start + size, FLUSH_CHUNK_SIZE); > + > ret = remove_section_mapping(start, start + size); > WARN_ON_ONCE(ret); > > -- > 2.21.0 >