Messages in this thread | | | Date | Tue, 2 Feb 2021 12:03:54 -0800 | From | Ira Weiny <> | Subject | Re: [PATCH v2 1/1] mm: Optimizing hugepage zeroing in arm64 |
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On Tue, Feb 02, 2021 at 01:12:24PM +0530, Prathu Baronia wrote: > In !HIGHMEM cases, specially in 64-bit architectures, we don't need temp > mapping of pages. Hence, k(map|unmap)_atomic() acts as nothing more than > multiple barrier() calls, for example for a 2MB hugepage in > clear_huge_page() these are called 512 times i.e. to map and unmap each > subpage that means in total 2048 barrier calls. This called for > optimization. Simply getting VADDR from page in the form of kmap_local_* > APIs does the job for us. We profiled clear_huge_page() using ftrace > and observed an improvement of 62%.
Nice!
> > Setup:- > Below data has been collected on Qualcomm's SM7250 SoC THP enabled > (kernel > v4.19.113) with only CPU-0(Cortex-A55) and CPU-7(Cortex-A76) switched on > and set to max frequency, also DDR set to perf governor. > > FTRACE Data:- > > Base data:- > Number of iterations: 48 > Mean of allocation time: 349.5 us > std deviation: 74.5 us > > v1 data:- > Number of iterations: 48 > Mean of allocation time: 131 us > std deviation: 32.7 us > > The following simple userspace experiment to allocate > 100MB(BUF_SZ) of pages and writing to it gave us a good insight, > we observed an improvement of 42% in allocation and writing timings. > ------------------------------------------------------------- > Test code snippet > ------------------------------------------------------------- > clock_start(); > buf = malloc(BUF_SZ); /* Allocate 100 MB of memory */ > > for(i=0; i < BUF_SZ_PAGES; i++) > { > *((int *)(buf + (i*PAGE_SIZE))) = 1; > } > clock_end(); > ------------------------------------------------------------- > > Malloc test timings for 100MB anon allocation:- > > Base data:- > Number of iterations: 100 > Mean of allocation time: 31831 us > std deviation: 4286 us > > v1 data:- > Number of iterations: 100 > Mean of allocation time: 18193 us > std deviation: 4915 us > > Reported-by: Chintan Pandya <chintan.pandya@oneplus.com> > Signed-off-by: Prathu Baronia <prathu.baronia@oneplus.com>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
FWIW, I have the same change in a patch in my kmap() changes branch. However, my patch also changes clear_highpage(), zero_user_segments(), copy_user_highpage(), and copy_highpage().
Would changing those help you as well?
Ira
> --- > include/linux/highmem.h | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/include/linux/highmem.h b/include/linux/highmem.h > index d2c70d3772a3..444df139b489 100644 > --- a/include/linux/highmem.h > +++ b/include/linux/highmem.h > @@ -146,9 +146,9 @@ static inline void invalidate_kernel_vmap_range(void *vaddr, int size) > #ifndef clear_user_highpage > static inline void clear_user_highpage(struct page *page, unsigned long vaddr) > { > - void *addr = kmap_atomic(page); > + void *addr = kmap_local_page(page); > clear_user_page(addr, vaddr, page); > - kunmap_atomic(addr); > + kunmap_local(addr); > } > #endif > > -- > 2.17.1 >
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