From: Alastair D'Silva <[email protected]>
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 <[email protected]>
---
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) {
+ 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
Comment below...
On Thu, 26 Sep 2019 at 12:18, Alastair D'Silva <[email protected]> wrote:
>
> From: Alastair D'Silva <[email protected]>
>
> 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 <[email protected]>
> ---
> 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
>
On Fri, 2019-09-27 at 08:37 +0200, Mark Marshall wrote:
> Comment below...
>
> On Thu, 26 Sep 2019 at 12:18, Alastair D'Silva <[email protected]>
> wrote:
> > From: Alastair D'Silva <[email protected]>
> >
> > 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 <[email protected]>
> > ---
> > 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.
Good catch, thankyou :)
> > + 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
> >
--
Alastair D'Silva
Open Source Developer
Linux Technology Centre, IBM Australia
mob: 0423 762 819