From c9f4cd71383576a916e7fca99c490fc92a289f5a Mon Sep 17 00:00:00 2001 From: Huang Ying Date: Fri, 17 Aug 2018 15:45:49 -0700 Subject: mm, huge page: copy target sub-page last when copy huge page Huge page helps to reduce TLB miss rate, but it has higher cache footprint, sometimes this may cause some issue. For example, when copying huge page on x86_64 platform, the cache footprint is 4M. But on a Xeon E5 v3 2699 CPU, there are 18 cores, 36 threads, and only 45M LLC (last level cache). That is, in average, there are 2.5M LLC for each core and 1.25M LLC for each thread. If the cache contention is heavy when copying the huge page, and we copy the huge page from the begin to the end, it is possible that the begin of huge page is evicted from the cache after we finishing copying the end of the huge page. And it is possible for the application to access the begin of the huge page after copying the huge page. In c79b57e462b5d ("mm: hugetlb: clear target sub-page last when clearing huge page"), to keep the cache lines of the target subpage hot, the order to clear the subpages in the huge page in clear_huge_page() is changed to clearing the subpage which is furthest from the target subpage firstly, and the target subpage last. The similar order changing helps huge page copying too. That is implemented in this patch. Because we have put the order algorithm into a separate function, the implementation is quite simple. The patch is a generic optimization which should benefit quite some workloads, not for a specific use case. To demonstrate the performance benefit of the patch, we tested it with vm-scalability run on transparent huge page. With this patch, the throughput increases ~16.6% in vm-scalability anon-cow-seq test case with 36 processes on a 2 socket Xeon E5 v3 2699 system (36 cores, 72 threads). The test case set /sys/kernel/mm/transparent_hugepage/enabled to be always, mmap() a big anonymous memory area and populate it, then forked 36 child processes, each writes to the anonymous memory area from the begin to the end, so cause copy on write. For each child process, other child processes could be seen as other workloads which generate heavy cache pressure. At the same time, the IPC (instruction per cycle) increased from 0.63 to 0.78, and the time spent in user space is reduced ~7.2%. Link: http://lkml.kernel.org/r/20180524005851.4079-3-ying.huang@intel.com Signed-off-by: "Huang, Ying" Reviewed-by: Mike Kravetz Cc: Andi Kleen Cc: Jan Kara Cc: Michal Hocko Cc: Andrea Arcangeli Cc: "Kirill A. Shutemov" Cc: Matthew Wilcox Cc: Hugh Dickins Cc: Minchan Kim Cc: Shaohua Li Cc: Christopher Lameter Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/memory.c | 30 +++++++++++++++++++++++------- 1 file changed, 23 insertions(+), 7 deletions(-) (limited to 'mm/memory.c') diff --git a/mm/memory.c b/mm/memory.c index 65bb59e031c9..175f344e1523 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -4705,11 +4705,31 @@ static void copy_user_gigantic_page(struct page *dst, struct page *src, } } +struct copy_subpage_arg { + struct page *dst; + struct page *src; + struct vm_area_struct *vma; +}; + +static void copy_subpage(unsigned long addr, int idx, void *arg) +{ + struct copy_subpage_arg *copy_arg = arg; + + copy_user_highpage(copy_arg->dst + idx, copy_arg->src + idx, + addr, copy_arg->vma); +} + void copy_user_huge_page(struct page *dst, struct page *src, - unsigned long addr, struct vm_area_struct *vma, + unsigned long addr_hint, struct vm_area_struct *vma, unsigned int pages_per_huge_page) { - int i; + unsigned long addr = addr_hint & + ~(((unsigned long)pages_per_huge_page << PAGE_SHIFT) - 1); + struct copy_subpage_arg arg = { + .dst = dst, + .src = src, + .vma = vma, + }; if (unlikely(pages_per_huge_page > MAX_ORDER_NR_PAGES)) { copy_user_gigantic_page(dst, src, addr, vma, @@ -4717,11 +4737,7 @@ void copy_user_huge_page(struct page *dst, struct page *src, return; } - might_sleep(); - for (i = 0; i < pages_per_huge_page; i++) { - cond_resched(); - copy_user_highpage(dst + i, src + i, addr + i*PAGE_SIZE, vma); - } + process_huge_page(addr_hint, pages_per_huge_page, copy_subpage, &arg); } long copy_huge_page_from_user(struct page *dst_page, -- cgit v1.2.3