On Thu, Aug 15, 2019 at 02:10:49PM +1000, Alastair D'Silva 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 16GB 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 | 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)
IMHO this begs for adding SZ_16G to include/linux/sizes.h and using it here
> +
> 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));
> + 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);
>
> --
> 2.21.0
>
--
Sincerely yours,
Mike.
